Frank Brothers Solutions for ICSE Class 10 Physics Chapter 6 Modern Physics

Page 271

Question 1. Define the term 'work function' of a metal.
Answer: The work function of a substance refers to the least amount of energy needed to release electrons from its metallic surface.
In simple words: The minimum energy a metal needs to set its surface electrons free is called its work function.

Exam Tip: Always state 'minimum amount of energy' to secure full marks. Simply saying 'energy required' will lose marks.

Question 2. Explain what conduction electrons are and how they are formed.
Answer: Electrons residing in the outermost orbits experience a weak gravitational-like pull from the nucleus, making them loosely attached. During solid formation, these weakly bound particles detach from their specific atoms to wander freely throughout the entire solid lattice. These are known as conduction electrons.
In simple words: Outer electrons are weakly held by the nucleus. When atoms group to make a solid, these electrons break free and move throughout the material, helping to conduct electricity.

Exam Tip: Clearly distinguish between bound electrons and conduction electrons by mentioning their position relative to the nucleus.

Question 3. What is thermionic emission? Mention one common application of this phenomenon.
Answer: When specific metals are raised to elevated temperatures, they discharge particles called thermions, which are actually electrons. This process is referred to as thermionic emission, and it serves a vital role in operating devices like the cathode ray oscilloscope.
In simple words: Heating certain metals makes them give off electrons (called thermions). This effect is used in cathode ray oscilloscopes to create images on screens.

Exam Tip: Remember to mention that the particles emitted during thermionic emission are called 'thermions' and they are identical to electrons.

Question 4. On what factors does the rate of electron emission from a hot surface depend?
Answer: The speed at which electrons are liberated from a hot surface is determined by:
(i) The work function of that particular substance.
(ii) The melting point of the substance.
In simple words: How fast a hot surface shoots out electrons depends on the material's work function and its melting temperature.

Exam Tip: State both work function and melting point clearly. High melting point and low work function are the key attributes of a good emitter.

Question 5. Why are materials with a low work function preferred as electron emitters?
Answer: Substances with a small work function are chosen for electron emission because they can release electrons at relatively lower temperatures.
In simple words: Metals that need less energy (low work function) are better because they start releasing electrons without needing to be heated too much.

Exam Tip: Explain that a lower work function reduces the threshold thermal energy needed to initiate emission, lowering the required temperature.

Question 6. State the unit in which the work function of a metal is usually expressed. Write its value in Joules.
Answer: The work function of a substance is typically measured in electron-volts (\(\text{eV}\)), where \( 1\text{ eV} = 1.6 \times 10^{-19}\text{ J} \).
In simple words: We measure work function in electron-volts. One electron-volt is equal to \( 1.6 \times 10^{-19} \) Joules of energy.

Exam Tip: Be careful with the conversion factor: \(1\text{ eV} = 1.6 \times 10^{-19}\text{ J}\). Do not confuse Joules with Coulombs.

Question 7. Answer the following questions based on a hot cathode ray tube:
(i) Name the charged particles emitted.
(ii) What is the magnitude of the charge on each of these particles?
(iii) State the approximate voltage applied to heat the filament.
(iv) What potential difference \(V_1\) is maintained between the anode and filament?
(v) How is the electron beam affected when it passes through a magnetic field?
Answer:
(i) The particles carrying charge are electrons.
(ii) Each of these particles has a charge of \( 1.6 \times 10^{-19}\text{ C} \).
(iii) To heat up the filament, a potential of nearly \( 3000\text{ V} \) is utilized.
(iv) The potential difference \(V_1\) set between the anode and filament spans a few hundred volts.
(v) When crossing a magnetic field, the electron stream experiences deflection.

In simple words: (i) The emitted particles are electrons. (ii) Each electron has a charge of \( 1.6 \times 10^{-19}\text{ C} \). (iii) The filament is heated using around \( 3000\text{ V} \). (iv) A few hundred volts of potential difference is set between the anode and the filament. (v) Passing through a magnetic field bends the path of the electron beam.

Exam Tip: In sub-part (ii), remember that the charge of an electron is measured in Coulombs (C), not Joules (J). Silently correct this common textbook typo in exams.

Question 8. Why must the pressure inside a cathode ray tube be kept very low?
Answer: A highly reduced pressure is maintained within a cathode ray tube because cathode rays consist of electrons, which possess extremely small mass. If gas molecules were present inside the tube, they would collide with and easily deflect the moving electrons, preventing them from reaching and striking the target screen accurately.
In simple words: The air inside the tube is pumped out so that the tiny, light electrons do not crash into air molecules and get knocked off course before hitting the screen.

Exam Tip: A common trap is to describe ionization instead of collision. Emphasize that collisions with gas molecules cause undesirable deflection.

Question 9. What is the purpose of applying a graphite coating on the inner side of a cathode ray tube near the fluorescent screen?
Answer: An internal coating of graphite is applied near the fluorescent screen of a cathode ray tube. When the electron beam strikes the screen, the surface accumulates a negative charge. To prevent this, the conductive graphite layer is linked to the ground (zero potential), which safely drains the extra charges. Without this path, the buildup of negative charge would repel incoming electrons, causing a drop in screen brightness.
In simple words: The graphite layer acts like a drain for extra negative charges. If they build up on the screen, they would push away new electrons and make the picture dimmer.

Exam Tip: Mention the terms 'electrostatic repulsion' and 'screen brightness' as examiners look for these key technical phrases.

Question 10. How can the brightness of the pattern on a CRT screen be controlled?
Answer: The intensity or brightness of the display on a cathode ray tube screen is adjusted by changing the electric potential delivered to the cathode.
In simple words: You can make the screen pattern brighter or dimmer by changing the voltage at the cathode.

Exam Tip: The cathode potential directly determines the number of emitted electrons, which controls the beam intensity and hence screen brightness.

Question 11. Describe the three main sections of a cathode ray tube.
Answer: A cathode ray tube is divided into three primary regions:
(i) **Electron gun**: This electrode configuration is designed to generate and focus a stream of electrons.
(ii) **Deflection system**: Located between the gun assembly and the screen, this section bends the path of the exiting electrons using two pairs of parallel plates set perpendicular to each other.
(iii) **Fluorescent screen**: Positioned at the far end, this target is covered in a blend of fluorescent and phosphorescent substances, where the latter ensures the image lingers on the screen for a short duration.
In simple words: A CRT has three parts: the electron gun to make the electron beam, the deflection system to steer the beam using plates, and the screen at the end which glows and keeps the image visible.

Exam Tip: Ensure you list all three components (Electron gun, Deflection system, Fluorescent screen) with their specific functions to get full marks.

Question 12. What effect will be observed on the screen of a CRT if:
(i) a hotter filament is used?
(ii) the anode voltage is increased?
Answer:
(i) Utilizing a filament at a higher temperature raises the total quantity of discharged electrons, which in turn enhances the brightness of the screen's luminous spot.
(ii) Elevating the anode potential forces the electrons into a faster, more tightly focused stream, yielding a more defined and smaller spot on the display.
In simple words: (i) A hotter filament makes more electrons, making the spot on the screen brighter. (ii) Raising the anode voltage speeds up and narrows the beam, making the spot sharper and smaller.

Exam Tip: Remember: Filament temperature regulates brightness (quantity of electrons), while anode voltage regulates focus and sharpness (speed of electrons).

Question 13. State two uses of a cathode ray tube.
Answer:
(i) Researchers in scientific laboratories utilize cathode ray tubes to transform electrical signals into visible images, and they are also employed in older television sets.
(ii) Medical professionals use these tubes in diagnostics (such as ECG and EEG machines) to translate physiological electrical signals from cardiac or brain activity into visual wave patterns.
In simple words: Cathode ray tubes are used by scientists to show electrical signals as lines on a screen, and by doctors to show heartbeats or brainwaves in ECG and EEG tests.

Exam Tip: Focus on the conversion of electrical signals into visual signals as the core function in laboratory and medical applications.

Question 14. Explain the role of the fluorescent and phosphorescent materials coated on a CRT screen.
Answer: The screen at the end of the tube is layered with a combination of phosphorescent and fluorescent agents. While the fluorescent coating generates a bright spot immediately upon electron impact, the phosphorescent component ensures that the formed image remains visible on the display for a brief period afterward.
In simple words: The fluorescent coat makes a glowing spot the moment electrons hit it, while the phosphorescent coat keeps that spot glowing for a little bit so we can see the full picture.

Exam Tip: Clearly differentiate: fluorescence is the instantaneous emission of light upon collision, whereas phosphorescence is the delayed emission (persistence).

Question 15. Compare the deflection of an electron beam in an electric field with that in a magnetic field.
Answer: Under an electric field, the electron stream is pulled toward the positive electrode. Its trajectory is parabolic inside the field region, turning into a straight line once it leaves.
Conversely, when traversing a magnetic field, the electrons experience a magnetic force determined by Fleming's Left-Hand Rule. This causes the beam to bend along a circular arc within the field. If the magnetic field is directed into the page (marked by 'X'), the electrons follow this curved path and then resume a straight trajectory upon leaving the field, oriented depending on their exit velocity.
In simple words: In an electric field, electrons curve like a thrown ball (parabolic) toward the positive plate. In a magnetic field, they bend in a circular curve determined by Fleming's Left-Hand Rule.

Exam Tip: Remember: Path is parabolic in an electric field but circular in a magnetic field. This is a very frequent exam question.

Page 281

Question 1. Name the elementary particles that make up an atom. Describe their arrangement within the atom.
Answer: An atom is composed of three primary subatomic constituents: protons, neutrons, and electrons. The protons and neutrons reside closely together in the center, forming the nucleus, while the electrons orbit around this heavy core in designated paths known as electronic orbits.
In simple words: An atom has three main particles: protons and neutrons stay in the middle (the nucleus), while electrons spin around them in orbits.

Exam Tip: Always specify that protons and neutrons lie inside the nucleus, while electrons revolve outside in discrete orbits.

Question 2. What is the nucleus of an atom? Which particles are present inside it?
Answer: Located at the center of an atom, the nucleus is its dense core, which contains protons and neutrons.
In simple words: The nucleus is the heavy center of an atom made of protons and neutrons.

Exam Tip: Clearly state that the nucleus contains both protons and neutrons, which are collectively referred to as nucleons.

Question 3. Define the following terms:
(i) Atomic number
(ii) Mass number
(iii) Atomic mass
Answer:
(i) **Atomic number**: This indicates the total number of protons found inside the nucleus. Since neutral atoms have an equal count of protons and electrons, this integer also represents the electron count.
(ii) **Mass number**: This is the combined total of both neutrons and protons residing in the atomic nucleus.
(iii) **Atomic mass**: This represents how heavy an atom of an element is in comparison to one-twelfth of the mass of a carbon-12 atom.
In simple words: (i) Atomic number is how many protons are in the nucleus. (ii) Mass number is the total number of protons plus neutrons. (iii) Atomic mass shows how heavy an atom is compared to a carbon atom.

Exam Tip: In definition of atomic mass, always use 'carbon-12 atom' as the reference standard to score full marks.

Question 4. Compare the penetrating power and ionizing power of \(\alpha\), \(\beta\), and \(\gamma\) radiations.
Answer:
(i) **Penetrating power**: Alpha (\(\alpha\)) particles possess the lowest ability to penetrate matter. Beta (\(\beta\)) particles are stronger, penetrating nearly 100 times deeper than alpha particles. Gamma (\(\gamma\)) rays exhibit the highest penetrating capacity, which is roughly 100 times greater than that of beta particles.
(ii) **Ionizing power**: Alpha (\(\alpha\)) particles have the strongest ionizing capability, which is about 100 times more powerful than that of beta (\(\beta\)) particles. Beta particles, in turn, ionize substances 100 times more effectively than gamma (\(\gamma\)) rays. Thus, gamma rays possess the weakest ionizing power.
In simple words: (i) Gamma rays penetrate the best, while alpha particles penetrate the least. (ii) Alpha particles are the best at ionizing (charging) other atoms, while gamma rays are the weakest at it.

Exam Tip: A useful mnemonic: alpha is the heaviest (highest ionization, lowest penetration), while gamma is massless (lowest ionization, highest penetration).

Question 5. What are beta (\(\beta\)) radiations similar to?
Answer: Beta (\(\beta\)) emissions share identical characteristics with a stream of high-speed electrons.
In simple words: Beta radiation is just like a fast-moving stream of electrons.

Exam Tip: Always equate beta radiation with fast-moving electrons to show their fundamental physical similarity.

Question 6. What are isotopes?
Answer: Isotopes are atoms belonging to the same chemical element that share an identical atomic number (\(Z\)) but possess different mass numbers (\(A\)).
In simple words: Isotopes are sibling atoms of the same element that have the exact same number of protons but a different number of neutrons.

Exam Tip: Clearly mention 'same atomic number' and 'different mass number'. These exact keywords are critical for scoring.

Question 7. State how isotopes differ in their physical and chemical properties.
Answer: Isotopes exhibit identical chemical behavior, but they differ in their physical characteristics.
In simple words: Isotopes behave the same way in chemical reactions, but they have different physical properties like mass.

Exam Tip: Chemical properties are determined by electrons (atomic number), which is why isotopes behave chemically identically.

Question 8. What are isobars?
Answer: Isobars are defined as atoms from different chemical elements that share the same mass number but have distinct atomic numbers.
In simple words: Isobars are different elements that happen to weigh the same because they have the same total mass number.

Exam Tip: Do not confuse isobars with isotopes. Isobars have different atomic numbers but the same mass number.

Question 9. State the similarities and differences between gamma (\(\gamma\)) radiations and X-rays.
Answer:
**Similarities**:
- Both gamma (\(\gamma\)) rays and X-rays can expose photographic plates.
- Both forms of electromagnetic radiation travel at the velocity of light. **Differences**:
- Gamma rays are emitted from unstable atomic nuclei during radioactive transitions, whereas X-rays are produced when fast-moving electrons are abruptly stopped by a dense metal target of a high melting point.
- Gamma rays demonstrate significantly greater penetrating capability compared to X-rays.
In simple words: Both gamma rays and X-rays travel at light speed and show up on film. However, gamma rays come from nuclear decay and can pass through thicker materials, while X-rays are made by stopping fast electrons with a metal plate.

Exam Tip: Always highlight that gamma rays have nuclear origin (emitted from nucleus), whereas X-rays are extra-nuclear (atomic origin).

Question 10. What are the changes in the mass number, atomic number, and position in the periodic table of an element when it emits:
(i) a \(\beta\) particle?
(ii) \(\gamma\) radiation?
Answer:
(i) **Beta (\(\beta\)) emission**: Since a beta particle carries a negative charge and negligible mass, its release leaves the atomic mass unchanged while increasing the atomic number by \( 1 \) unit. Consequently, the position of the element shifts one step to the right in the same row of the periodic table.
(ii) **Gamma (\(\gamma\)) emission**: Gamma rays are completely neutral and massless. Therefore, emitting gamma radiation does not alter either the mass number or the atomic number of the element, and its placement in the periodic table remains unchanged.
In simple words: (i) When an atom loses a beta particle, its mass stays the same but its atomic number goes up by 1, moving it one spot right in the periodic table. (ii) Gamma rays have no mass or charge, so emitting them changes nothing about the atom's identity or position.

Exam Tip: Beta emission increases the atomic number by 1, shifting the element to the right, because a neutron converts into a proton inside the nucleus.

Question 11. State the representation of \(\alpha\), \(\beta\), and \(\gamma\) emissions and explain how they affect the atomic number of a radioactive element.
Answer:
(i) An **alpha (\(\alpha\)) particle** is denoted as \(_2\text{He}^4\). Containing two protons, the emission of an alpha particle causes the atomic number of the decaying nucleus to decrease by \( 2 \) units.
(ii) A **beta (\(\beta\)) particle** is denoted as \(_{-1}\text{e}^0\). Emitting a beta particle results in an increase in the atomic number of the nucleus by \( 1 \) unit.
(iii) **Gamma (\(\gamma\)) radiation** possesses neither charge nor mass, meaning its emission leaves the atomic number of the element unaltered.
In simple words: (i) Alpha particles have 2 protons, so losing one lowers the atomic number by 2. (ii) Beta particles have a -1 charge, so losing one raises the atomic number by 1. (iii) Gamma rays have no charge, so losing them doesn't change the atomic number.

Exam Tip: Write down the symbols \(_2\text{He}^4\) and \(_{-1}\text{e}^0\) correctly. Placing the mass and atomic numbers in their correct positions is essential.

Question 12. Explain how the emission of \(\alpha\), \(\beta\), and \(\gamma\) radiations affects the mass number of a radioactive element.
Answer:
(i) Represented as \(_2\text{He}^4\), an **alpha (\(\alpha\)) particle** consists of 2 protons and 2 neutrons, giving it a mass of 4 units. Consequently, emitting an alpha particle reduces the mass number of the parent nucleus by \( 4 \) units.
(ii) Since a **beta (\(\beta\)) particle** is denoted as \(_{-1}\text{e}^0\), its emission does not alter the mass number of the nucleus.
(iii) **Gamma (\(\gamma\)) radiation** has zero rest mass, so its emission leaves the atomic mass of the element completely unchanged.
In simple words: (i) Alpha particles have 4 units of mass, so emitting one lowers the atom's mass number by 4. (ii) Beta particles have almost no mass, so losing one doesn't change the mass number. (iii) Gamma rays are massless, so they don't affect the mass number at all.

Exam Tip: Remember: Beta and gamma emission do not change the mass number. Only alpha decay reduces the mass number (by 4 units).

Question 13. A radioactive source emits three types of radiations: \(\alpha\), \(\beta\), and \(\gamma\). State:
(i) which of these are charged?
(ii) which radiation is the most penetrating?
(iii) which radiation travels at the speed of light?
(iv) which radiation has the largest mass?
Answer:
(i) The emissions that carry electrical charge are the **alpha (\(\alpha\))** and **beta (\(\beta\))** radiations.
(ii) The **gamma (\(\gamma\))** rays stand out as the most penetrating among the three.
(iii) **Gamma (\(\gamma\))** radiation propagates at the speed of light.
(iv) **Alpha (\(\alpha\))** particles carry the greatest mass of all the emitted radiations.
In simple words: (i) Alpha and beta radiations are charged. (ii) Gamma rays can penetrate materials the best. (iii) Gamma rays travel as fast as light. (iv) Alpha particles are the heaviest.

Exam Tip: Ensure you address all sub-parts systematically. Sub-part questions are marked independently, so clear labeling is crucial.

Question 14. Define radioactivity. Why is it considered a nuclear phenomenon?
Answer: Radioactivity represents the spontaneous, random release of particles and rays from an unstable atomic core. Because these emissions originate directly from the nucleus itself, radioactivity is classified as a nuclear phenomenon.
In simple words: Radioactivity is when an unstable nucleus randomly shoots out particles on its own. Since this happens inside the nucleus, it is a nuclear event.

Exam Tip: Highlight that radioactivity is independent of physical and chemical conditions (like temperature or pressure) since it is a purely nuclear event.

Question 15. Describe how the emission of a beta (\(\beta\)) particle affects the atomic number and mass number of a nucleus.
Answer: A beta particle is represented by \(_{-1}\text{e}^0\). When a nucleus undergoes beta decay, its atomic number increases by \( 1 \) unit, while its mass number remains completely unaffected.
In simple words: Losing a beta particle makes the atomic number go up by 1, but doesn't change the mass number.

Exam Tip: Beta decay increases the atomic number by 1 but leaves the mass number unchanged. Do not write that the mass decreases.

Question 16. Define atomic number and atomic mass. Are these quantities conserved during radioactive beta decay?
Answer:
(i) **Atomic number**: This signifies the count of protons within the nucleus, which also equals the electron count in a stable neutral atom.
(ii) **Atomic mass**: This represents the mass of an atom calculated relative to the mass of a carbon-12 atom (which is defined as 12).
Yes, the total nucleon count (mass number) and the total charge (atomic number conservation in terms of charge conservation) remain conserved throughout a beta (\(\beta\)) decay process.
In simple words: Atomic number is the number of protons, and atomic mass is how heavy the atom is compared to carbon-12. Both total mass and charge are conserved during beta decay.

Exam Tip: In beta decay, charge conservation is represented by the atomic number increase, and total nucleon conservation keeps the mass number constant.

Question 17. Explain how alpha, beta, and gamma radiations behave when passing through a magnetic field perpendicular to their path.
Answer:
(i) **Alpha (\(\alpha\)) particles**: Being relatively heavy and positively charged, they experience less deflection in a magnetic field. According to Fleming's Left-Hand Rule, they bend in an upward direction.
(ii) **Beta (\(\beta\)) particles**: Because they have an extremely small mass and a negative charge, they undergo significant deflection in the downward direction.
(iii) **Gamma (\(\gamma\)) rays**: Lacking both mass and charge, they travel in a straight path completely unaffected by the magnetic field.
In simple words: Alpha particles bend slightly upwards because they are heavy and positive. Beta particles bend strongly downwards because they are very light and negative. Gamma rays do not bend at all because they have no charge.

Exam Tip: Use Fleming's Left-Hand Rule to determine the direction of deflection. Remember that the direction of current is opposite to electron (beta) flow.

Question 18. (a) Explain how alpha, beta, and gamma radiations behave in an electric field.
(b) Why is a radioactive source placed inside a thick lead container with a narrow opening?
Answer:
(a) Behavior in an electric field:
(i) **Alpha (\(\alpha\)) particles**: Due to their large mass and positive charge, they experience a smaller deflection and bend toward the negatively charged plate.
(ii) **Beta (\(\beta\)) particles**: Since they are extremely light and carry a negative charge, they are deflected heavily toward the positive plate.
(iii) **Gamma (\(\gamma\)) rays**: Having neither mass nor electrical charge, they travel straight ahead without any deflection.
(b) The radioactive emitter is stored inside a dense lead box with a single opening because it releases energetic radiations. The thick lead walls successfully absorb emissions moving in other directions, allowing only a collimated beam to exit through the open top, which prevents dangerous radiation leaks.
In simple words: (a) Alpha particles bend slightly toward the negative plate, beta particles bend strongly toward the positive plate, and gamma rays do not bend. (b) A thick lead container blocks harmful radiation from escaping in all directions, letting it exit safely only through a small opening.

Exam Tip: Clearly draw the trajectories in the electric field: alpha bends towards the negative plate, beta towards the positive plate, and gamma passes straight.

Page 282

Question 19. A radioactive nucleus \(_{84}\text{X}^{202}\) emits an \(\alpha\) particle and then a \(\beta\) particle to form a daughter nucleus \(_b\text{Y}^a\). Find the values of \(a\) and \(b\).
Answer: Let the initial nucleus be \(_{84}\text{X}^{202}\).
1. When it emits an \(\alpha\) particle (\(_2\text{He}^4\)), the mass number reduces by \( 4 \) and the atomic number reduces by \( 2 \): \[ _{84}\text{X}^{202} \longrightarrow {_{82}\text{W}^{198}} + {_2\text{He}^4} \]
2. Subsequently, when this intermediate nucleus emits a \(\beta\) particle (\(_{-1}\text{e}^0\)), its atomic number increases by \( 1 \) while its mass number remains unchanged: \[ _{82}\text{W}^{198} \longrightarrow {_{83}\text{Y}^{198}} + {_{-1}\text{e}^0} \] Comparing the final daughter nucleus with \(_b\text{Y}^a\), we get:
- Mass number \( a = 198 \)
- Atomic number \( b = 83 \)
In simple words: An alpha decay reduces mass by 4 and atomic number by 2, turning \(_{84}\text{X}^{202}\) into \(_{82}\text{X}^{198}\). A beta decay then increases the atomic number by 1, making it \(_{83}\text{Y}^{198}\). Thus, \( a = 198 \) and \( b = 83 \).

Exam Tip: To solve such decay chains, perform the calculations step-by-step: first reduce mass by 4 and atomic number by 2 for alpha, then add 1 to the atomic number for beta.

Question 20. Which radioactive emissions do not cause any change in the mass number of a nucleus?
Answer: The mass number of a radioactive nucleus remains unaltered when it undergoes beta (\(\beta\)) or gamma (\(\gamma\)) emission.
In simple words: Emitting beta or gamma radiations does not change the mass of the atom.

Exam Tip: Only alpha decay alters the mass number (decreases by 4). Beta and gamma decays leave the mass number unchanged.

Question 21. Which radioactive emission does not cause any change in the atomic number of an element?
Answer: The atomic number of a radioactive element is unaffected during gamma (\(\gamma\)) decay.
In simple words: When an atom emits gamma radiation, its atomic number stays exactly the same.

Exam Tip: Gamma emission is purely an energy-releasing process. It has zero effect on the nucleus's composition or charge.

Question 22. A radioactive nucleus \(_Z\text{X}^A\) first emits a \(\beta\) particle and then an \(\alpha\) particle to give a daughter nucleus \(_Q\text{Y}^P\). Express \(P\) and \(Q\) in terms of \(A\) and \(Z\).
Answer: We start with the parent element \(_Z\text{X}^A\).
1. After undergoing a beta (\(\beta\)) emission (\(_{-1}\text{e}^0\)), the atomic number increases by \( 1 \), and the mass number remains unchanged: \[ _Z\text{X}^A \longrightarrow {_{Z+1}\text{W}^A} + {_{-1}\text{e}^0} \]
2. Next, after emitting an alpha (\(\alpha\)) particle (\(_2\text{He}^4\)), the atomic number decreases by \( 2 \), and the mass number decreases by \( 4 \): \[ _{Z+1}\text{W}^A \longrightarrow {_{Z-1}\text{Y}^{A-4}} + {_2\text{He}^4} \] Comparing the resulting daughter nucleus with \(_Q\text{Y}^P\), we find:
- \( P = A - 4 \)
- \( Q = Z - 1 \)
In simple words: First, a beta decay raises the atomic number by 1 to \( Z+1 \). Then, an alpha decay lowers the atomic number by 2 and the mass by 4, leaving us with atomic number \( Z-1 \) and mass \( A-4 \). So, \( P = A - 4 \) and \( Q = Z - 1 \).

Exam Tip: When dealing with variables like A and Z, show the intermediate step of decay clearly to prevent simple algebraic calculation errors.

Question 23. How are artificial radioactive substances produced? What are they called? Mention two uses of such substances.
Answer: Artificial radioactive substances are generated by bombarding lighter atomic nuclei with energetic particles like alpha particles, protons, or neutrons. The radioactive materials produced through this technique are known as radioisotopes.
Two major applications of radioisotopes include:
(i) Emissions from Radium are used to treat and improve various skin conditions.
(ii) Radioactive Sulphur (\(^{35}\text{S}\)) serves as a tracer to evaluate the effectiveness and impacts of different fungicides.
In simple words: We make artificial radioactive materials (called radioisotopes) by hitting light atoms with fast particles. They are used to treat skin conditions and to study how fungicides affect crops.

Exam Tip: Keep the examples specific, such as cobalt-60 for cancer and iodine-131 for thyroid, to earn full marks in application-based questions.

Question 24. State four precautions that must be observed while handling radioactive substances.
Answer: When working with radioactive materials, the following safety measures must be strictly followed:
(i) Always use specialized forceps to handle radioactive sources; they must never be touched directly with bare hands.
(ii) Ensure that active sources are never pointed toward any individual.
(iii) Avoid consuming any food or beverages in areas where radioactive isotopes are handled, to prevent accidental ingestion or contamination.
(iv) Smoking is strictly prohibited near any radioactive source.
In simple words: Never touch radioactive things with your hands (use forceps), never point them at anyone, do not eat or drink around them, and do not smoke near them.

Exam Tip: When asked for safety precautions, make sure to write at least three distinct points with explanations, rather than brief one-word answers.

Question 25. Why must radioactive substances never be touched with bare hands?
Answer: Radioactive materials must never be handled directly because the intense ionizing radiation they emit can damage living tissues, leading to serious medical conditions such as radiation burns, cataracts, leukemia, sterility, or other severe health issues.
In simple words: Touching radioactive materials directly is extremely dangerous because the radiation can cause skin burns, cataracts, cancer, or permanent damage to your body.

Exam Tip: Always emphasize that direct handling risks cellular damage, which is why distance (using forceps) is the best protection.

Page 283

Question 1. Answer the following multiple choice questions:
(a) A copper atom is represented as \(_{29}\text{Cu}^{63}\). It contains:
(i) 29 protons and 34 electrons
(ii) 34 protons and 29 electrons
(iii) 29 protons and 29 electrons
(iv) 34 protons and 34 electrons

(b) A radioactive nucleus \(_{86}\text{Ra}^{226}\) decays to form a daughter nucleus \(_b\text{X}^a\) after emitting 2 \(\alpha\) particles, 1 \(\beta\) particle, and a \(\gamma\) ray. The values of \(a\) and \(b\) are:
(A) \(a = 218, b = 82\)
(B) \(a = 218, b = 83\)
(C) \(a = 222, b = 84\)
(D) \(a = 220, b = 83\)

(c) A radioactive element \(_{92}\text{X}^{238}\) emits an \(\alpha\) particle. The atomic number and mass number of the new element will be:
(A) 90 and 234
(B) 94 and 238
(C) 91 and 234
(D) 90 and 238

(d) An element \(_{92}\text{P}^{239}\) emits a \(\beta\) particle. The atomic number and mass number of the resulting daughter nucleus \(_b\text{Q}^a\) are:
(A) \(a = 239, b = 91\)
(B) \(a = 240, b = 93\)
(C) \(a = 239, b = 93\)
(D) \(a = 239, b = 92\)

(e) Which of the following radiations are deflected by a magnetic field?
(i) Only alpha particles
(ii) Only beta particles
(iii) Only gamma radiations
(iv) Both alpha and beta particles
Answer:
(a) **(iii) 29 protons and 29 electrons** - The atomic number of copper is 29, which indicates the number of protons and also equals the number of electrons in a neutral copper atom. The number of neutrons is found by subtracting the atomic number from the mass number: \( 63 - 29 = 34 \). Therefore, option (iii) is correct.
(b) **(B) \(a = 218, b = 83\)** - Emitting 2 alpha particles reduces the mass number by 8 and the atomic number by 4, forming \(_{82}\text{X}^{218}\). Emitting 1 beta particle then increases the atomic number by 1, forming \(_{83}\text{X}^{218}\). Gamma ray emission causes no change. Thus, \(a = 218\) and \(b = 83\).
(c) **(A) 90 and 234** - Emitting an alpha particle reduces the atomic number by 2 (92 to 90) and the mass number by 4 (238 to 234).
(d) **(C) \(a = 239, b = 93\)** - Undergoing beta decay leaves the mass number unchanged at 239 while the atomic number increases by 1 to 93.
(e) **(iv) Both alpha and beta particles** - Both carry electrical charge and therefore experience forces in a magnetic field, while neutral gamma rays pass straight through.
In simple words: This question covers standard multiple-choice problems on proton/electron counts, decay sequences (alpha, beta, and gamma), and magnetic deflection of charged particles.

Exam Tip: MCQ questions test your concept speed. Write out the formulas quickly on rough paper before ticking the option.

Page 284

Question 2. Define radioactivity. Answer the following questions:
(a) What type of charge do \(\alpha\) particles carry?
(b) Which of the three radiations is the most penetrating?
(c) Which radiation carries no electric charge?
Answer: Radioactivity refers to the spontaneous breakdown of an unstable, naturally occurring atomic nucleus, resulting in the release of alpha (\(\alpha\)), beta (\(\beta\)), and gamma (\(\gamma\)) radiations.
(a) Alpha (\(\alpha\)) particles carry a positive charge.
(b) Gamma (\(\gamma\)) radiation possesses the highest penetrating ability.
(c) Gamma (\(\gamma\)) radiation carries zero electrical charge.
In simple words: Radioactivity is the automatic breakdown of an unstable nucleus that shoots out radiation. (a) Alpha particles are positive. (b) Gamma rays penetrate materials best. (c) Gamma rays have no charge.

Exam Tip: Disintegration of an unstable nucleus is the central theme of radioactivity. Be sure to include 'spontaneous' in your definition.

Question 3. Complete the following statements:
(a) An electron has...
(b) Neutrons have...
Answer:
(a) **(ii) a mass less than that of a proton.** An electron is an extremely light subatomic particle, and its mass is far smaller than that of a proton.
(b) **(iv) no electric charge.** Neutrons are electrically neutral particles residing in the nucleus and carry no charge.
In simple words: (a) An electron is much lighter than a proton. (b) A neutron is neutral and has no charge.

Exam Tip: Make sure you read the options carefully. Protons and neutrons are much heavier than electrons, which have negligible mass.

Question 4. Based on the atomic model shown below, answer the following:
(a) What is the nature of the charge on the nucleus?
(b) Express the total charge on the nucleus in terms of the number of protons \(p\).
Answer:
The heavy central region represents the nucleus, around which electrons move in circular orbits.
(a) The atomic nucleus carries a positive electrical charge.
(b) Since each proton has a positive charge of \( +1.6 \times 10^{-19}\text{ C} \) and neutrons are completely neutral, the total nuclear charge can be expressed as \( p \times 1.6 \times 10^{-19}\text{ C} \), where \( p \) represents the total proton count.
In simple words: (a) The nucleus in the center is positively charged. (b) Since only protons in the nucleus have charge, the total charge is the number of protons multiplied by the charge of a single proton (\( 1.6 \times 10^{-19}\text{ C} \)).

Exam Tip: In the Bohr model, remember that the nucleus is positively charged, and the orbital electrons are negatively charged.

Question 5. Outline the properties of alpha (\(\alpha\)), beta (\(\beta\)), and gamma (\(\gamma\)) radiations emitted by a radioactive source.
Answer: A radioactive source is capable of emitting three distinct forms of radiation: alpha (\(\alpha\)) particles, beta (\(\beta\)) particles, and gamma (\(\gamma\)) rays. Their key properties are described below:

Alpha (\(\alpha\)) Particles

• They consist of Helium nuclei, represented as \(_2\text{He}^4\).
• They carry a net positive charge.
• Each alpha particle has a rest mass of roughly \( 4\text{ a.m.u.} \)
• They exhibit the highest ionizing capacity, which is approximately 100 times stronger than that of beta particles.
• They travel at slower speeds than light, typically around \( 1 \times 10^7\text{ m/s} \).
• They possess the weakest penetrating power.
• Due to their high mass, they experience relatively small deflections in electric and magnetic fields.

Beta (\(\beta\)) Particles

• They are high-speed electrons, represented as \(_{-1}\beta^0\).
• They carry a negative electrical charge.
• The rest mass of a beta particle is extremely small and considered negligible.
• Their velocity is high and comparable to the speed of light.
• They have moderate ionizing capability (about 100 times less than alpha but 100 times more than gamma).
• Their penetrating power is intermediate - nearly 100 times greater than that of alpha particles.
• Being very light, they are easily and highly deflected by electric and magnetic fields, in a direction opposite to alpha particles.

Gamma (\(\gamma\)) Radiations

• They are highly energetic electromagnetic waves.
• They carry no electrical charge.
• They have zero rest mass.
• They propagate at the speed of light (\( 3 \times 10^8\text{ m/s} \)).
• They possess the weakest ionizing capability.
• They exhibit the highest penetrating capacity, about 100 times greater than beta particles.
• They are completely undeflected by both electric and magnetic fields.

In simple words: Alpha particles are heavy, positive, slow, and easy to block, but they ionize very strongly. Beta particles are light, negative, fast, and moderately penetrating. Gamma rays are massless, neutral, travel at light speed, and are extremely hard to block, but they barely ionize.

Exam Tip: This comprehensive comparison is highly scoring. Create a neat table or structured bulleted lists in the exam to stand out.

Question 6. A uranium nucleus is represented as \(_{92}\text{U}^{235}\).
(a) What is the number of protons in this nucleus?
(b) State the number of electrons in a neutral uranium atom.
(c) What changes when we consider another isotope of uranium?
(d) How many protons are present in the isotope \(_{92}\text{U}^{238}\)?
Answer:
(a) The atomic number of uranium is 92. Since the atomic number represents the proton count, there are \( 92 \) protons in the nucleus of \(_{92}\text{U}^{235}\).
(b) In a neutral uranium atom, the number of electrons equals the number of protons, which is \( 92 \).
(c) Different isotopes of the same element share the same atomic number but possess different mass numbers. Therefore, for another isotope of uranium, the mass number (which is 235 here) will change.
(d) Because all isotopes of uranium must have the same atomic number (92) to remain uranium, the isotope \(_{92}\text{U}^{238}\) also contains \( 92 \) protons.
In simple words: (a) It has 92 protons. (b) A neutral atom has 92 electrons. (c) A different isotope of uranium will have a different mass number. (d) Every uranium isotope has 92 protons, so \(_{92}\text{U}^{238}\) still has 92 protons.

Exam Tip: Isotopes always share the exact same number of protons (atomic number), which is 92 for all uranium isotopes.

Question 7. Compare the behavior of alpha, beta, and gamma radiations with respect to:
(i) deflection in a magnetic field.
(ii) deflection in an electric field.
(iii) penetrating power through a lead sheet.
Answer:
(i) **Deflection in a magnetic field**:
- **Alpha (\(\alpha\))**: Because of their relatively large mass and positive charge, they show a minor deflection.
- **Beta (\(\beta\))**: Being much lighter and negatively charged, they exhibit a large deflection in the opposite direction.
- **Gamma (\(\gamma\))**: Since they have no mass or charge, they travel straight without any deflection.
(ii) **Deflection in an electric field**:
- **Alpha (\(\alpha\))**: They are pulled slightly toward the negative plate due to their positive charge.
- **Beta (\(\beta\))**: Their negative charge causes them to deflect strongly toward the positive plate.
- **Gamma (\(\gamma\))**: They are completely unaffected and continue in a straight line.
(iii) **Penetration through a lead sheet**:
- **Alpha (\(\alpha\))**: They have the lowest penetrating capability and are easily stopped by lead.
- **Beta (\(\beta\))**: They penetrate about 100 times more than alpha particles, thus passing further into the lead.
- **Gamma (\(\gamma\))**: They possess the highest penetrating capacity, 100 times greater than beta particles, allowing them to penetrate deep into lead.
In simple words: (i) Alpha deflects slightly, beta deflects strongly in the opposite direction, and gamma does not deflect in a magnetic field. (ii) Alpha goes toward the negative plate, beta toward the positive plate, and gamma goes straight. (iii) Gamma penetrates lead the deepest, followed by beta, while alpha is easily stopped.

Exam Tip: For physical vs chemical properties, relate chemical properties to electronic configuration (atomic number) and physical properties to mass number.

Question 8. Define isotopes. Give the names and symbols of the three isotopes of hydrogen.
Answer: Isotopes are atoms of the same element that share the same atomic number \(Z\) but differ in their mass number \(A\). For example, hydrogen has three distinct isotopes: protium (\(_1\text{H}^1\)), deuterium (\(_1\text{H}^2\)), and tritium (\(_1\text{H}^3\)).
In simple words: Isotopes are versions of an element that have the same number of protons but different masses. Hydrogen has three isotopes: protium, deuterium, and tritium.

Exam Tip: Remember the hydrogen isotopes: Protium (\(_1\text{H}^1\)) has no neutrons, Deuterium (\(_1\text{H}^2\)) has 1 neutron, and Tritium (\(_1\text{H}^3\)) has 2 neutrons.

Question 9. (a) Define Mass number and Atomic number.
(b) How do isotopes of an element differ in atomic number and atomic mass?
(c) State the medical, agricultural, and industrial applications of radioactivity.
Answer:
(a) **Definitions**:
- **Mass number**: This is the sum of the total protons and neutrons residing within the atomic nucleus.
- **Atomic number**: This is the count of protons present in the nucleus, which also equals the electron count in a stable, neutral atom.
(b) **Isotopes**: Isotopes have the same atomic number but possess different mass numbers (atomic masses).
(c) **Applications of Radioactivity**:

Medical Uses:

• Radium emissions are utilized to successfully treat various skin conditions.
• Cobalt-60 (\(^{60}\text{Co}\)) radiation is widely employed in cancer therapy.
• Radioactive Iodine (\(^{131}\text{I}\)) is used for diagnosing and treating thyroid abnormalities.

Agricultural Uses:

• Radioactive Phosphorus (\(^{32}\text{P}\)) helps researchers study plant metabolic processes.
• Radioactive Sulphur (\(^{35}\text{S}\)) is applied to analyze the performance and safety of fungicides.
• Gamma (\(\gamma\)) rays are used to destroy agricultural pests and insects.

Industrial Uses:

• Radioactive gauges help regulate the thickness of paper, plastic, and metal sheets during manufacturing.
• Radioisotopes are used to measure the rate of wear and tear in mechanical bearings.
• They are also used to detect internal cracks in castings, welds, and structural metal components.

In simple words: (a) Mass number is protons plus neutrons; atomic number is just the number of protons. (b) Isotopes have the same atomic number but different mass numbers. (c) Radioactivity helps treat skin diseases, cancer, and thyroid issues; it helps study plants and kill pests; and it is used in factories to check thickness and find cracks in metal.

Exam Tip: State both the name of the isotope and its field of application clearly. Combining name + use (like Carbon-14 for dating or Cobalt-60 for cancer) is highly effective.

Question 10. Summarize the comparison between alpha (\(\alpha\)), beta (\(\beta\)), and gamma (\(\gamma\)) radiations in a tabular format.
Answer: Here is a detailed comparison of the properties of alpha, beta, and gamma radiations:

In simple words: This table compares the nature, charge, mass, speed, ionizing capability, and deflection properties of alpha, beta, and gamma rays.

Exam Tip: A tabular comparison is the easiest way to contrast alpha, beta, and gamma. Keep the table clean, aligned, and write standard values.

Question 11. State the precautions that must be taken while handling radioactive substances.
Answer: When handling radioactive sources, the following precautions should be followed:
(i) Always handle radioactive materials with forceps rather than using bare hands.
(ii) Ensure active radioactive sources are never pointed at anyone.
(iii) Avoid eating or drinking in areas where radioactive isotopes are used to prevent food contamination.
(iv) Smoking is strictly prohibited near any radioactive substance.
In simple words: Avoid touching radioactive elements directly, don't point them at people, keep food away from them, and don't smoke nearby.

Exam Tip: 'Never touched by hand' and 'use forceps' are standard grading keywords. Be sure to write them exactly.

Question 12. Define radioactive decay. Write the balanced equation representing the alpha decay of \(_{92}\text{U}^{238}\) to Thorium (\(\text{Th}\)), addressing any common errors in textbook representations of Thorium's atomic number.
Answer: Radioactive decay is the process in which an unstable parent nucleus disintegrates to form a more stable daughter nucleus, accompanied by the emission of ionizing radiations. Note: Some textbook printings erroneously give Thorium an atomic number of 92, whereas its correct atomic number is 90. The symbolic nuclear equation representing this alpha decay is: \[ _{92}\text{U}^{238} \longrightarrow {_{90}\text{Th}^{234}} + {_2\text{He}^4} \]
In simple words: Radioactive decay is when an unstable atom breaks down to make a new, more stable atom. For example, Uranium-238 loses an alpha particle to become Thorium-234.

Exam Tip: Always write the balanced nuclear equation. The sum of subscripts and superscripts on both sides must be equal.

Question 13. Write the symbolic equation for the beta decay of a sodium isotope \(_{11}\text{Na}^{24}\) to magnesium (\(\text{Mg}\)).
Answer: The beta decay equation of sodium-24 into a stable magnesium nucleus is written as: \[ _{11}\text{Na}^{24} \longrightarrow {_{12}\text{Mg}^{24}} + {_{-1}\text{e}^0} \]
In simple words: When sodium-24 emits a beta particle (an electron), its atomic number increases by 1 to become magnesium-24, while its mass stays the same.

Exam Tip: Sodium-24 decaying to Magnesium-24 is a classic beta-decay example. Write the beta particle as \(_{-1}\text{e}^0\) to balance the atomic numbers.

Question 14. (a) What is thermionic emission?
(b) On what factors does the rate of thermionic emission depend?
Answer:
(a) Thermionic emission is the process where heated metal surfaces release electrons (known as thermions) at high temperatures.
(b) The intensity of this emission depends on:
(i) The work function of the metal.
(ii) The melting point of the metal.
In simple words: (a) Heating certain metals makes them give off electrons. (b) How many electrons are released depends on the metal's work function and its melting point.

Exam Tip: Remember: rate of thermionic emission is inversely related to work function (lower work function = higher emission rate).

Question 15. (a) Draw a labeled diagram of a cathode ray oscilloscope (CRO) showing its components.
(b) List two main applications of cathode ray tubes (CRT).
Answer:
(a) Here is the schematic diagram showing the internal components of a Cathode Ray Oscilloscope (CRO):
(b) **Applications of CRTs**:
(i) In research laboratories, they display electrical signals on a screen, and they were also utilized as picture tubes in older television sets.
(ii) In healthcare, they convert vital signals (like cardiac and brain activities) into readable visual waveforms in electrocardiograms (ECG) and electroencephalograms (EEG).
In simple words: (a) The diagram shows how electrons travel from the cathode, through deflecting plates, to draw an image on the screen. (b) CRTs are used in labs to display waves and in hospitals for ECG and EEG heartbeat displays.

Exam Tip: When drawing a CRO diagram, make sure to clearly demarcate the three main parts: the electron gun, the deflection plates, and the screen.

Question 16. (a) Define the term radioactivity.
(b) State some examples of radioactive isotopes.
Answer:
(a) Radioactivity is the automatic, random breakdown of an unstable atomic nucleus of a naturally occurring isotope, releasing energetic alpha (\(\alpha\)), beta (\(\beta\)), and gamma (\(\gamma\)) radiations.
(b) Common examples of radioisotopes include Cobalt-60 (\(^{60}\text{Co}\)), Iodine-131 (\(^{131}\text{I}\)), Phosphorus-32 (\(^{32}\text{P}\)), Sodium-24 (\(^{24}\text{Na}\)), and Sulphur-35 (\(^{35}\text{S}\)).
In simple words: (a) Radioactivity is the automatic splitting of unstable nuclei that emits rays. (b) Examples of radioisotopes are Cobalt-60, Iodine-131, and Sodium-24.

Exam Tip: Ensure you spell the isotope names correctly. Medical applications often carry specific, high-weightage marks.

Question 17. Compare the characteristics of alpha, beta, and gamma radiations.
Answer:

Alpha (\(\alpha\)) Particles

• **Nature**: Consists of helium nuclei (\(_2\text{He}^4\)).
• **Charge**: Positively charged (\(+2e\)).
• **Mass**: Approximately 4 a.m.u.
• **Speed**: Roughly \(1 \times 10^7\text{ m/s}\).
• **Ionizing Power**: Strongest.
• **Penetrating Power**: Weakest.
• **Deflection**: Experiences minor deflection in electric/magnetic fields.

Beta (\(\beta\)) Particles

• **Nature**: Stream of high-speed electrons (\(_{-1}\text{e}^0\)).
• **Charge**: Negatively charged (\(-1e\)).
• **Mass**: Negligible.
• **Speed**: Nearly equal to the speed of light.
• **Ionizing Power**: Moderate (100 times less than alpha).
• **Penetrating Power**: Moderate (100 times more than alpha).
• **Deflection**: Strongly deflected in fields, in the opposite direction of alpha.

Gamma (\(\gamma\)) Radiations

• **Nature**: High-frequency electromagnetic waves.
• **Charge**: Uncharged (Neutral).
• **Mass**: Zero.
• **Speed**: Travels at the speed of light (\(3 \times 10^8\text{ m/s}\)).
• **Ionizing Power**: Weakest.
• **Penetrating Power**: Strongest (100 times more than beta).
• **Deflection**: Unaffected by electric or magnetic fields.

In simple words: This list outlines how alpha, beta, and gamma radiations compare in their charge, mass, speed, ionizing, and penetrating strengths.

Exam Tip: Be sure to state the relative properties clearly. For instance, alpha has the least penetration while gamma has the most.

Question 18. What safety rules must be followed when working near radioactive elements?
Answer: When working in close proximity to radioactive materials, the following safety regulations must be observed:
(i) Use remote handling tools or forceps to carry radioactive materials instead of direct contact.
(ii) Avoid aiming a radioactive emitter toward yourself or anyone else.
(iii) Do not ingest food or beverages in areas containing radioactive material to avoid ingestion risk.
(iv) Smoking is completely banned in labs where radioactive sources are stored.
In simple words: Always use forceps to hold radioactive stuff, never point it at someone, don't eat in the lab, and do not smoke near radioactive materials.

Exam Tip: When discussing precautions, write clear and actionable points rather than vague descriptions.

Question 19. State the uses of radioactive isotopes in the fields of medicine, agriculture, and industry.
Answer: Radioisotopes have several practical applications across various sectors:

Medicine:

• Rays from radium sources are utilized to treat various skin ailments.
• Cobalt-60 (\(^{60}\text{Co}\)) therapy is a standard treatment for cancer patients.
• Iodine-131 (\(^{131}\text{I}\)) is widely applied to inspect and cure thyroid abnormalities.

Agriculture:

• Phosphorus-32 (\(^{32}\text{P}\)) acts as a tracer to study plant metabolic systems.
• Sulphur-35 (\(^{35}\text{S}\)) is used to test the environmental safety of fungicides.
• Gamma radiations are used to eradicate agricultural pests.

Industry:

• Radioactive gauges maintain the uniform thickness of paper, plastic, and metal foils during production.
• Isotopes are used as tracers to monitor the wear rate in machinery bearings.
• They can find hidden hairline cracks in welds and steel castings.

In simple words: Radioisotopes are used to treat skin diseases, cancer, and thyroid problems; help study plant growth and kill bugs; and are used in factories to measure thickness and find metal cracks.

Exam Tip: Memorize at least two uses for each category (medical, agricultural, industrial) as they are frequently asked as short answers.

Question 20. What is background radiation? List four sources of background radiation. Is it possible to completely shield ourselves from these radiations?
Answer: Background radiation refers to the low-temperature microwave radiation reaching the Earth's surface from cosmic space in all directions, as well as terrestrial ionizing radiation. Four primary sources of this background radiation are:
(a) Solar cosmic rays.
(b) Earth's rocks containing traces of radioactive substances.
(c) Terrestrial isotopes that occur naturally.
(d) Man-made artificial radioisotopes. No, it is impossible to completely isolate or shield ourselves from background radiation since it is present everywhere in the environment.
In simple words: Background radiation is the low-level radiation that surrounds us from space and the Earth. Its sources include the sun, rocks, natural isotopes, and artificial isotopes. We cannot completely escape it because it is present everywhere.

Exam Tip: Define background radiation precisely. Emphasize that it is omnipresent, making complete shielding practically impossible.