CBSE Class 7 Science Revision Worksheet Set 03

Topic : Flow of Heat

Long Question/Answers-

Question 1: Explain how heat is conducted from the heated end of a rod to its cold end.
Answer: Heat is conducted from the heated end of a rod to its cold end through the effective vibration of its molecules. Molecules of the rod starts vibrating as heat is supplied to it. When one end of the rod heats up, the molecules of that end starts vibrating and colliding with the nearby molecules to make them unstable. These molecules further hit their neighbouring molecules to transfer the heat. In this way, heat is transferred from one end of the rod to its other end.

Question 2: With an example of each, explain the uses of good and bad conductors of heat.
Answer: Good conductors of heat are used where we want to transfer heat faster from one point to the other. For example, cooking utensils are made of metals like brass, steel and aluminium, which are good conductors of heat. Though silver and copper are best conductors of heat but not usually used in cooking utensils as they are expensive. Bad conductors of heat are used where we want to stop the heat from getting transferred or where we do not want the heat to be lost or gained from the surroundings. For example, handles of cooking utensils are made of wood or plastic, which are bad conductors of heat. Hence, the handles don't heat up during cooking, thereby allowing us to hold the utensils comfortably.

Question 3: Describe the process of convection of heat.
Answer: The process of transference of heat through a fluid (liquid or gas) is called convection. It can be observed that when water is heated, water near the flame gets hot and starts rising up. On the other hand, cold water moves down from the sides of the flask, towards the source of heat. Then, this water becomes hot and rises up. This process continues till all the water present in the flask gets heated. This process of heat transfer is called convection.

Question 4: Explain with the help of diagrams how sea and land breezes are set up.
Answer: During the day, land gets heated up faster than the sea. So, the air above the land becomes warmer and lighter and moves upward. The air above the sea, which is relatively cooler, rushes to take its place. This results in to sea breeze during the day.

During the night, the land cools faster than the sea. Therefore, the air above the land is cooler and denser, while the air above sea is warmer and lighter. The air above the sea will move upwards and the cooler air from the land will rush to take its place. This causes land breeze during the night.

Question 5: Black objects absorb more heat than white or polished ones. Give two daily uses of this principle.
Answer: The everyday uses of the principle that black objects absorb more heat than white or polished ones are as follows:
1) Cooking utensils have black-polished/black-painted outer surface to absorb more heat. This helps in cooking the food in less time. 2) During winters, we wear black or dark coloured clothes, as these can absorb more heat and keep us warm than the white or dull coloured ones.

Question 6: Black objects radiate more heat than white objects. Give two everyday uses of this principle.
Answer: Black objects radiate more heat than white objects. Two everyday uses of this principle are:
1. Refrigerator pipes are painted with a dull black colour so that they can radiate the heat to the surrounding and cool themselves down.
2. Hot plates are coloured black so that it can radiate more heat energy to serve its purpose efficiently.

Question 7: Draw a neat labelled diagram of a thermos flask. How does it prevent transfer of heat by conduction, convection or radiation?
Answer: Thermos flask consists of double glass or metal walls with a space in between them. Air is completely sucked out of this space, and after that the walls are sealed at the neck or at the bottom of the flask. This vacuum is created to prevent heat loss due to conduction and convection, as both these methods require a medium to transfer heat. Then, the walls are silvered. This silver polish prevents the heat loss through radiation, as heat from inside the flask is radiated back to it and the external heat is reflected back to the surrounding. Finally, the vessel is put inside a metallic case with a plastic or cork support on both sides so as to protect the glass from breaking. At last, the mouth of the vessel is closed by a stopper made from an insulating material like plastic or cork.

Question 8: Two test tubes full of water are heated-one from below and the other near the top. In which case will the water heat up faster and why?
Answer: The test tube which is heated from below will heat up faster. When we heat water from below, the molecules at the bottom of the water start heating and expanding due to which they become light and move upwards. On moving upwards, they transfer the heat energy to other molecules. After transferring their energy, they contract and return to the bottom again. This cycle continues till the entire water gets heated through the convection mode. If water is heated from above, the heated molecules at the top will change their state to form steam, as they can hardly transfer the heat energy to the bottom layer due to the convection current

The Global Edge School - Ahead Of the Learning Curve Page 1

I. Answer the following question in detail.

1. Where is bile produced? What component of food does it digest?

2. Explain the digestion of food in ruminants?

3. What are the properties of a compound?

4. Differentiate between formula and symbol.

5. Write the formula of calcium carbonate showing the steps involved?

6. Balance the equation

Na + H₂O → NaOH + H₂

7. Define the following

a. Atomicity b. Valency c. Sericulture d. Radiation

8. What are factors that decide the quality of wool?

9. What are the effects of heat?

10. Explain the how heat causes expansion with the help of an experiment?

11. What precautions are used for using a clinical thermometer?

12. Explain the steps involved in the production of silk?

13. Why do woollen clothes keep us warm than cotton clothes?

14. Explain one natural phenomenon that occurs due to convection of current in air.

15. Write the symbols of following elements and radicals.

16. Magnesium b. Zinc c. Sulphate d. Copper e. Nitrate f. Phosphate.

17. Convert 350 C to 0F

18. How does the presence of acid in the stomach help?

19. Why room heaters have bright polished surface?

20. Why is mercury used as an indicator in a thermometer?

21. Write the function of different types of teeth?

22. Why are two thin woollen blankets warmer than a thick woollen blanket? 23. What are the factors that affect the soil formation? 24. Neela took 50ml of water in a measuring jar. She started pouring it over 50g of soil taken in a funnel. Soon the water started dripping from the funnel. 11ml of water was left in the measuring cylinder. What was the percentage of water retained by the soil?

The Global Edge School Revision Worksheet 2012-13

The Global Edge School - Ahead Of the Learning Curve Page 2

II. Fill in the blanks using appropriate answers.

1. The inner wall of the small intestine has fingerlike projection called _______________

2. Amoeba ingest its food with the help of __________________

3. The animal that lives on liquid food ________________

4. The wave like action that helps the muscles to push down the food ____________

5. The hydrochloric acid in the stomach helps in the digestion of _____________________

6. The partially digested food in rumiants is known as _______________

7. ______________ is made up of elements combined together in a fixed ratio

8. The formula of potassium is _______________

9. The elements present in a molecule of water is __________________ and _____________

10. The atom an of element that can exist independently is known as __________________

11. The formula of Magnesium sulphate is ______________

12. The complex compound that form animal fibre is _______________

13. Heat causes increase in _________________

14. The temperature at which the Celsius and Fahrenheit scale is the same ________________

15. The temperature scale used for scientific purpose _________________

16. The temperature range in the Fahrenheit clinical thermometer_________________

17. The heat of the sun reaches us by _______________________

18. The combining capacity of an element is its ____________________.

19. The transfer of heat in liquids is by _______________

20. The vaccum present in the thermos flask helps to reduce the flow of heat by _________________

21. The thermometer used to measure the temperature of boiling water ______________

22. Decayed organic matter is turned into dark coloured material is called_____________

23. The water holding capacity is higher in _________________

24. Loamy soil is a mixture of _________________

25. Sorters disease is caused by____________________

Diagrams to practice :

Draw labeled diagrams of (i) Human digestive system (ii) Thermos Flask (iii) Life cycle of Moth (iv) Sea and land Breeze (v) Ingestion of food in amoeba and hydra.

SECTION –A

Q1. Fill in the blanks

1. In insects,exchange of gases takes place through ______________________.

2. Amarbel is an example of__________________.

3. Gills are the ______________ of the skin.

4. _________ breaks down the starch into sugar.

5. _____________ in tongue detects the taste of food.

SECTION-B

Q2. State TRUE and FALSE

1. Turmeric is a synthetic indicator.

2. Tooth decay is caused by the presence of a base.

3. Solutions which are neither acidic nor basic are called indicators.

4. When an ant bytes it injects formic acid into the skin.

5. All the changes are chemical.

SECTION-C

Q4. Answer the following questions.

1. What is time period?

2. What is odometer and speedometer?.

3. What is a simple pendulum?

4. A simple pendulum takes 32 seconds to complete 20 oscillations. Find the time period?

5. The distance between two stations is 500 kms. A train takes 2 hours to cover this distance. Calculate speed in meters per second?

Topic : Flow of Heat

Short Question/Answers-

Question 1: What conditions are necessary for transfer of heat from one body to another by conduction?
Answer : Conditions necessary for the transfer of heat from one body to the other through conduction are as follows:
1. The two objects must be in contact with each other.
2. The temperatures of both the objects must be different.

Question 2: Differentiate between good and bad conductors of heat.
Answer : Good conductors of heat
Materials that can easily conduct heat through them are good conductors of heat.
For example, iron, copper and silver
Bad conductors of heat
Materials that cannot conduct heat through them are insulators of heat or bad conductors of heat.
For example, glass, wood and plastic

Question 3: Why do woolen clothes keep us warmer in winters than cotton clothes?
Answer : Woollen fibre comprises spaces between them that traps the air. Since air is a bad conductor of heat, it will not allow the body heat to escape, thereby keeping the body warm in winters. However, in a cotton fibre, such spaces are absent; hence, it can not keep us warmer as compared to the woollen clothes.

Question 4: Why are ventilators in houses provided at the top of walls?
Answer : Ventilators are installed on the top most part of the walls because the air we breathe out is warmer and lighter, and moves upwards. This stale air escapes through the ventilators, and fresh and cooler air enters the room through the doors and windows to take its place.

Question 5: How does heat from the sun reach us? At what speed does this transfer of heat take place?
Answer : Heat from the Sun reaches us through the process of radiation. There is millions of miles of empty space between the Earth and the Sun; therefore, only through radiation can heat be transferred to the Earth from the Sun, as it does not require any medium. The radiant heat travels similar to the speed of light.

Question 6: What is the function of the polished curved surface at the back of the heating rod in a room heater?
Answer : The polished curved surface at the back of the heating rod in a room heater reflects the radiant heat from the heating rod. Thus, the radiant heat spreads across the room, thereby making the room warmer.

Topic : Heat and its  Effect

Question 1: List four effects that heat produces.
Answer : Four effects of heat are as follows:
1. Change in temperature - When water is heated, its temperature increases and it starts boiling.
2. Change in State - On boiling water, steam is evolved, i.e., the its liquid state changes to its gaseous state.
3. Expansion - While heating water, some of it overflows due to expansion, i.e., increase in volume.
4. Chemical change - When vegetables are boiled in water while cooking, they become soft and their taste changes. Thus, a chemical change occurs in the vegetables.

Question 2: What does a bimetallic strip consist of?
Answer : A bimetallic strip consists of two metal strips, one of iron and the other of brass, bolted together firmly. The two metals expand at different rate on heating. Brass expands more than iron on heating, thereby bending the bimetallic strip towards the iron strip. And, after returning to the room temperature, the strip straightens as before.

Question 3: A steel bridge expands in summer. What precautions are taken to make sure this expansion does not damage the bridge?
Answer : A steel bridge expands in the summers. One of its end is fixed and the other end is made to rest on rollers with enough space for expansion. This allows the bridge to expand easily without taking any damage.

Question 4: How are temperature and hotness of a body related?
Answer : Hotter the body, higher is its temperature. Hence, hotness of a body is directly proportional to its temperature.

Question 5: What do you mean by 'upper fixed point'?
Answer : Upper fixed point is the temperature at which pure water boils at the sea level. In the Celsius scale, the upper fixed point is 100oC, and in the Fahrenheit scale, it is 212oF.

Question 6: Why does a clinical thermometer have a kink in its stem?
Answer : As soon as the thermometer is taken out of our mouth, i.e., from a hotter region to a colder region, the mercury in it starts contracting and tends to flow back into the bulb. The kink in the stem prevents the mercury from falling back immediately, thereby giving us the accurate reading of our body temperature 

a. Label the parts A, B, C, D
b. What does the above diagram represent.
c. Write in one line the function of A,B, C and D in the above diagram.

2. Identify Who am I
a. I give red colour to blood
b. I am used to measure your heart beat.
c. I fight against germs, which enter your body.
d. I am the fluid part of the blood.

Topic : Heat and its Effect 

Long question/answers-

Question 1: Explain why a substance expands on heating.
Answer : When a substance is heated, its molecular movement increases. Due to this, the average distance between the molecules also increases, thereby increasing the volume of the substance, i.e., expanding the substance. However, the movement of molecules depends upon the state of matter. Solids have tightly packed molecules; hence, least movement of molecules takes place leading to minimal expansion. In liquids, the molecules are less tightly packed as compared to solids; hence, they expand more than solids. Molecules of gases have no bonding at all; therefore, gases expand the most among the three.

Question 2: Give one example where expansion on heating is put to good use. Explain the working with the help of a labelled diagram.
Answer : Automatic fire alarm is an example of expansion on heating, which is put to good use. The fire alarm works on the principle that different solids expand differently when heated. An automatic fire alarm consists of a bimetallic strip which have two different metals strips, iron and brass, bolted together firmly. Brass expands more than iron on heating. Therefore, when fire will reach this bimetallic strip, the brass will expand more thereby bending it towards the iron strip. Due to this bending of the strip, the circuit for the electric bell is completed and it starts ringing as the fire alarm. Once the strip cools down, it will return to its original shape, i.e., straighten up to break the circuit and stop the alarm.

Question 3: Explain why gases expand more than liquids and solids.
Answer : Gases comprise loosely packed molecules as compared to that of liquids and solids. Therefore, when the gases are heated, there is a huge vibration in their molecules, thereby increasing the average distance between them. In case of solids and liquids, there is a strong bonding between their molecules; therefore on heating, these molecules vibrate but less comparatively to gases where the bonding between molecules is almost nil. Hence, in solids and liquids, expansion will take place but less than gases.

Question 4: Explain with the help of a labelled diagram an experiment to show that liquids expand when heated.
Answer : Take a flask filled with a liquid up to its brim. Take a rubber cork with a hole in it and insert a glass tube in it. Now, fit the cork tightly on the mouth of the flask. You will notice that the the level of the liquid will rise in the tube. Note down the level in the tube and start heating the flask. Initially, the liquid level will drop, but after a few moments it will start rising. At first the liquid level will fall due to the expansion of the flask on heating; then when this heat reaches the liquid, it starts expanding. Only at this time you will notice that the level of liquid is rising in the tube. After cooling back the liquid to its normal temperature, the level will drop again.

Question 5: Expansion on heating can be a nuisance. Explain giving two examples.
Answer : Expansion due to heating can be a nuisance. This is explained below with the help of the following examples: 1. Railway tracks are made up of iron which expands during the summers. Hence, if no gap is left between two conjoined tracks, they will bend and result into serious accidents.

Question 6: What precautions will you take while measuring temperature with a laboratory thermometer? What extra precaution will you take while measuring body temperature with a clinical thermometer?
Answer : Precautions that should be taken while using a laboratory thermometer for measuring temperature are as follows:
• It should be properly washed before and after use.
• It should be kept upright while reading the temperature.
• Its bulb should be properly dipped into the liquid or perfectly touched to the surface of the material whose temperature is being measured.
• Its bulb should not touch the surface of the container in which the material or liquid has been placed.
• It should be handled with care, as it is made up of a glass tube.
Precautions that should be taken while using a clinical thermometer for measuring body temperature are as follows:
• Sterilise the thermometer using an antiseptic solution before and after its use.
• Ensure that the mercury level is below 35oC before measuring the temperature.
• Take the reading keeping the level of mercury along the line of sight.
• Avoid holding it by its bulb while reading the temperature.

Q1 - Fill in the blanks

(1) The weight of air acting on a surface causes…………………………………….

(2) Warm air is …………………………………………than cold air.

(3) Cyclones are know as ……………………………………………..in the American Continent.

(4) The centre of a cyclone is a cloudless, calm area called the----------------------

(5) High speed winds are accompanied by ………………………………………..air pressure.

Q2 - Solve the crossword given below with the help of the clues.

Across: 4. Wind flows from a region of high pressure to a region of … ……Pressure.

5. A violent, dark, funnel- shaped cloud of hot air caused by spinning.

8. Pressure exerted by air.

9. Cyclones are know as ……………in Japan and Philippines.

10. These winds carry a lot of moisture.

Down; 1, Violent storm with an intense spiral.

2. Moving air.

3. The envelope of air surrounding our earth.

6. A storm accompanied with lightning and thunder.

7. This is required to form clouds.

Q3 - Give at least two examples from your own daily experience to confirm that air exerts pressure.

Topic : Flow of Heat

Fill in the blanks:-

1. The heat is transferred from one place to another place by conduction, convection and radiation.

2. In solids heat is transferred by conduction.

3. All liquids are bad conductors of heat.

4. Materials which do not allow heat to be conducted through them are called insulators.

5. The primary mode of heat transfer in a liquid is convection.

6. Sea and land breezes are actually convection current.

7. In vacuum heat energy can travel by the process of radiation.

8. The fastest method of heat transfer is radiation.

9. The thermos flask minimizes transfer of heat by conduction, convection and radiation.

10. Heat is transferred from hot to cold body.

11. Molecular movement takes place during convection.

12. Heat from the sun reaches us by the process of radiation.

1. Name the organism which grows on bread and makes it appear greenish black. What type of reproduction takes place in it.

2. Complete the following sentences:-

a. The flowers which contain only the pistil or the stamens are called ______.

b. The process of fusion of male and female gamete is called______.

c. The transfer of pollen from anther to stigma of same flower is called ____.

d. The basic unit of time is ____.

e. Distances between two cities are measured in _____.

f. Combination of two or more cells is called_______.

g. The coil of wire in a bulb which gets heated on passing electric current through it is called___.

3. Convert 50 km/hr into m/s.

1. Collect the pictures of the following animals and paste them in your HW notebook. Write and explain how each one of them is adapted to suit their environment.(in maximum three lines).

a) Fish b)tiger c}giraffe

2. Give reason

a) Toucans have a long beak

b) Penguins live in a group and remain huddled together

3. Give the difference between weather and climate of a place.

4. Name the following

a. Instrument to measure the maximum and minimum temperature during a day.

b. Instrument to measure wind speed.

c. Instrument to measure the amount of rainfall.

1. Why does our earth appear blue from share?

2. Which day is celebrated as world water days?

3. What is an aquifer? How is water pumped out of an aquifer.

4. What is

a. a canopy b. the crown of tree

5. What are decomposers?

6. Explain why forests are called green lung?

A. Fill in the blanks:

Question 1. The valency of oxygen is _____
Answer: 2
In simple words: Oxygen requires 2 electrons to complete its octet, giving it a valency of 2.

Exam Tip: Remember that valency is the combining capacity and does not carry a positive or negative sign.

Question 2. The atomicity of an element having formula \(X_3\) is _____
Answer: 3
In simple words: Atomicity is the total number of atoms present in one molecule of an element.

Exam Tip: Look at the subscript in the molecular formula to determine atomicity directly.

Question 3. The combining capacity of an element is called _____
Answer: valency
In simple words: Valency tells us how many bonds an atom can form with other atoms.

Exam Tip: This is a standard definition of valency often asked in one-word answers.

Question 4. A food _____ is made up of several food chains.
Answer: web
In simple words: A food web is an interconnected network of multiple food chains in an ecosystem.

Exam Tip: Do not confuse food chain (a single straight line of eating and being eaten) with food web (interconnected chains).

Question 5. The level of ground water is called the _____
Answer: water table
In simple words: The upper limit of the water-saturated layer under the ground is the water table.

Exam Tip: Water table varies from place to place and depends on rainfall.

Question 6. Formula of glucose is _____
Answer: \(C_6H_{12}O_6\)
In simple words: Glucose is a simple sugar made of carbon, hydrogen, and oxygen atoms.

Question 7. Buildings and roads reduce _____ of water by the soil.
Answer: seepage (or infiltration)
In simple words: Paved concrete surfaces prevent rainwater from soaking into the ground.

Exam Tip: Urbanization decreases groundwater recharge due to concrete cover.

Question 8. A convex lens _____ a parallel beam of light incident on it.
Answer: converges
In simple words: A convex lens bends light rays inward to meet at a single focal point.

Exam Tip: Convex lenses are converging lenses, whereas concave lenses are diverging lenses.

Question 9. Cyclonic winds tends to circulate around the _____ of the cyclone.
Answer: eye
In simple words: Winds swirl at high speed around the calm, low-pressure center called the eye.

Exam Tip: The center of a cyclone is calm and clear, known as the eye of the storm.

Question 10. The boiling point of water is _____ \(^{\circ}\text{C}\)
Answer: 100
In simple words: Water starts boiling and changing into vapor at 100 degrees Celsius under standard atmospheric pressure.

Exam Tip: Always mention the unit degrees Celsius with temperature values.

B. Define the following

Question 1. Element
Answer: An element is a pure substance made up of only one kind of atom that cannot be broken down into simpler substances by physical or chemical means. Examples include iron, oxygen, and gold.
In simple words: An element is the purest form of matter containing identical atoms.

Exam Tip: Emphasize that elements consist of only one type of atom.

Question 2. Mixture
Answer: A mixture is a substance formed by physically combining two or more different substances in any proportion, where each substance retains its individual chemical properties. Examples include air, salt water, and soil.
In simple words: A mixture is a combination of different substances not chemically joined together.

Exam Tip: Mention that components of a mixture can be separated by physical methods.

Question 3. Cyclone
Answer: A cyclone is a large-scale system of winds that rotate inward around a low-pressure center, accompanied by violent storms, heavy rainfall, and high-speed destructive winds.
In simple words: A cyclone is a massive spinning storm with high-speed winds and heavy rain.

Exam Tip: Key terms to include are low-pressure center and high-speed rotating winds.

Question 4. Atomicity
Answer: Atomicity is defined as the total number of atoms present in a single molecule of an element. For example, oxygen gas (\(O_2\)) has an atomicity of 2.
In simple words: Atomicity tells how many atoms make up one molecule.

Exam Tip: State examples like monoatomic, diatomic, and polyatomic molecules to score full marks.

Question 5. Symbiosis
Answer: Symbiosis is a close and long-term biological interaction between two different biological organisms, where both organisms benefit mutually from each other. An example is lichens, where algae and fungi live together.
In simple words: Symbiosis is a partnership between two organisms where both help each other survive.

Exam Tip: Always include the key aspect that both organisms derive mutual benefit.

Question 6. Valency
Answer: Valency is the combining capacity of an atom of an element, determined by the number of electrons lost, gained, or shared to achieve a stable electronic configuration.
In simple words: Valency is the number of chemical bonds an atom can form.

Exam Tip: Relate valency to electrons in the outermost shell.

Question 7. Weathering
Answer: Weathering is the breaking down or dissolving of rocks and minerals on Earth's surface by agents such as water, ice, acids, salt, plants, animals, and changes in temperature.
In simple words: Weathering is the breaking down of rocks into smaller particles over time.

Exam Tip: Distinguish weathering (breaking in place) from erosion (transportation of particles).

Question 8. Spectrum
Answer: A spectrum is a band of colors produced when white light is split into its constituent wavelengths, such as when light passes through a prism, resulting in the rainbow colors (VIBGYOR).
In simple words: A spectrum is the multicolored band of light seen when white light splits.

Exam Tip: Mention dispersion of light to explain how a spectrum is formed.

C. Multiple choice questions:

Question 1. There are about 117 different
(a) Molecules
(b) Elements
(c) Mixture
(d) None of the options
Answer: (b) Elements
There are currently about 118 known elements in the periodic table.
In simple words: The periodic table consists of various chemical elements.

Exam Tip: Remember that elements are pure substances listed in the periodic table.

Question 2. What kind of motion does a simple pendulum have?
(a) Oscillatory
(b) Circular
(c) Rectilinear
(d) None of the options
Answer: (a) Oscillatory
A simple pendulum swings back and forth repetitively about its mean position, which is periodic and oscillatory motion.
In simple words: Back and forth motion is called oscillatory motion.

Exam Tip: Oscillatory motion is a specific type of periodic motion.

Question 3. Digested food is absorbed in the
(a) Stomach
(b) Small intestine
(c) Rectum
(d) Oesophagus
Answer: (b) Small intestine
The inner walls of the small intestine have finger-like projections called villi that absorb digested food into the blood stream.
In simple words: The small intestine is the main site for food absorption in the human body.

Question 4. The smallest particle of an element is
(a) Molecules
(b) Atoms
(c) Compounds
(d) All of the options
Answer: (b) Atoms
An atom is the basic building block and the smallest particle of an element that retains its chemical properties.
In simple words: An atom is the tiniest particle of any element.

Exam Tip: Molecules are made up of two or more atoms combined together.

Question 5. Which of these is not a standard unit
(a) Gram
(b) Meter
(c) Handspan
(d) Second
Answer: (c) Handspan
Handspan is a non-standard unit of measurement because it varies from person to person. Gram, meter, and second are SI standard units.
In simple words: Handspan changes with hand size, so it is not a standard unit.

Exam Tip: Standard units provide uniform measurements accepted worldwide.

Question 6. The symbol of iron is
(a) I
(b) F
(c) Fe
(d) Ir
Answer: (c) Fe
The symbol Fe comes from the Latin name for iron, 'ferrum'.
In simple words: Iron is represented by the chemical symbol Fe.

Question 1. Define valency in terms of hydrogen.
Answer: Valency in terms of hydrogen is defined as the number of hydrogen atoms that can combine with or displace one atom of an element. For example, in water (\(H_2O\)), one oxygen atom combines with two hydrogen atoms, so the valency of oxygen is 2.
In simple words: Valency can be measured by counting how many hydrogen atoms bond with an element.

Exam Tip: Hydrogen is taken as a standard reference with a valency of 1.

Question 2. Differentiate between element and compound.
Answer:
1. An element is made up of only one kind of atom, whereas a compound is formed by the chemical combination of two or more different elements.
2. Elements cannot be broken down into simpler substances by chemical reactions, whereas compounds can be broken down into their constituent elements.
3. Example of an element: Oxygen (\(O_2\)). Example of a compound: Water (\(H_2O\)).
In simple words: Elements have one type of atom, while compounds are made of different elements chemically combined.

Exam Tip: Always present differences in a comparative format for better clarity.

Question 3. State and explain laws of reflection with diagram.
Answer:
The two laws of reflection are:
1. The incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.
2. The angle of incidence (\(i\)) is always equal to the angle of reflection (\(r\)), expressed as \(\angle i = \angle r\).
In simple words: The incoming light ray, the normal line, and the reflected ray lie on the same flat surface, and the angle of incidence equals the angle of reflection.

Exam Tip: Label angles \(i\) and \(r\) clearly with respect to the normal line, not the mirror surface.

Question 4. Draw a well labelled diagram showing the different layers of soil.
Answer:
The soil profile consists of three main layers called horizons, plus bedrock:
1. A-Horizon (Topsoil): Dark colored, rich in humus and minerals, home to many organisms.
2. B-Horizon (Middle layer / Subsoil): Lighter colored, denser, contains less humus but more minerals.
3. C-Horizon: Made of small lumps of rocks with cracks and crevices.
4. Bedrock: Hard solid layer of rock lying beneath all soil layers.
In simple words: Soil is arranged in layers from topsoil down to solid bedrock.

Exam Tip: Practice drawing the horizons in correct vertical sequence from top to bottom.

Question 5. Write an experiment to show that air exerts pressure in all directions.
Answer:
Aim: To demonstrate that air exerts pressure in all directions.
Materials required: A glass tumbler, water, and a stiff postcard.
Procedure:
1. Fill the glass tumbler completely with water so that no air gap remains at the top.
2. Cover the mouth of the tumbler completely with the stiff postcard.
3. Hold the card firmly with one hand and invert the glass upside down carefully.
4. Slowly remove your hand from the postcard.
Observation: It is observed that the postcard does not fall, and the water stays inside the glass.
Conclusion: The air pressure acting upward from beneath the postcard is greater than the downward pressure exerted by the water inside, proving that air exerts pressure in all directions.
In simple words: Air pushes objects from all directions, which keeps the card in place when a glass of water is inverted.

Exam Tip: Ensure the glass is filled to the brim with water to prevent air pockets during inversion.

Question 6. What is conservation? How does planting trees help in ground water conservation?
Answer:
Conservation: Conservation is the careful preservation, protection, and management of natural resources to prevent their depletion and ensure their availability for future generations.
Role of trees in groundwater conservation:
1. Trees act as natural barriers that slow down the flow of rainwater across the land, giving water more time to seep into the soil.
2. The roots of trees create porous channels in the soil that facilitate deep percolation and recharge of groundwater.
In simple words: Conservation means protecting resources. Trees slow down flowing rainwater, helping it soak deep into the ground.

Question 7. Why are earthworms called farmer's friend?
Answer:
Earthworms are called farmer's friends because:
1. They burrow through the soil, making it loose and porous, which allows air and water to reach plant roots easily.
2. Their waste (vermicast) is rich in organic nutrients, acting as a natural fertilizer that increases soil fertility.
In simple words: Earthworms loosen the soil for roots and provide natural fertilizer through their waste.

Exam Tip: Mention both soil aeration and nutrient addition in your answer.

Question 8. Differentiate between renewable and non renewable resources.
Answer:
1. Renewable resources are inexhaustible and can be replenished naturally within a short time (e.g., solar energy, wind energy, water). Non-renewable resources are limited in supply and take millions of years to form once exhausted (e.g., coal, petroleum, natural gas).
2. Renewable resources are generally clean and eco-friendly, whereas non-renewable fossil fuels cause pollution when burned.
In simple words: Renewable resources never run out, while non-renewable resources get depleted permanently with use.

Exam Tip: Give at least two clear examples for each category.

Question 9. Give the functions of (a) mucous (b) hydrochloric acid in stomach
Answer:
(a) Mucous: Protects the inner lining of the stomach from the corrosive action of hydrochloric acid.
(b) Hydrochloric acid: Kills harmful bacteria entering with food and creates an acidic medium required for digestive enzymes (like pepsin) to function properly.
In simple words: Mucus shields the stomach wall, while acid kills germs and helps digest food.

Question 10. Draw a distance time graph for following data.
Time (in minutes): 4.05am, 4.10am, 4.15am, 4.20am
Distance (in kms): 5, 10, 15, 20
Answer:
Steps to draw the graph:
1. Draw X-axis representing time (in minutes) and Y-axis representing distance (in kms).
2. Choose a suitable scale, such as 1 cm = 5 minutes on X-axis and 1 cm = 5 kms on Y-axis.
3. Plot the data points: (4:05, 5), (4:10, 10), (4:15, 15), and (4:20, 20).
4. Join all plotted points with a straight line, which indicates uniform speed.
In simple words: Plot time on the horizontal axis and distance on the vertical axis, then connect the points with a straight line.

Exam Tip: A straight-line distance-time graph always indicates uniform motion (constant speed).

Question 11. Distinguish between real and virtual images along with example of each.
Answer:
1. A real image can be obtained on a screen, whereas a virtual image cannot be obtained on a screen.
2. A real image is always inverted, whereas a virtual image is always erect.
3. Example of real image: Image formed on a cinema screen by a projector. Example of virtual image: Image formed by a plane mirror.
In simple words: Real images can be caught on a screen and are upside down, while virtual images cannot be caught on a screen and are upright.

Question 12. A bus takes 4hours30minutes to cover a distance of 270km between New Delhi and Shimla. Find the speed of the bus in km/hr.
Answer:
Distance (\(d\)) = 270 km
Time (\(t\)) = 4 hours 30 minutes = \(4 + \frac{30}{60}\) hours = 4.5 hours
Speed = \(\frac{\text{Distance}}{\text{Time}}\)
Speed = \(\frac{270}{4.5} = \frac{2700}{45} = 60\) km/hr
In simple words: Divide the total distance by total time in hours to get the speed in km/hr.

Exam Tip: Always convert minutes into decimal hours before calculating speed.

Question 13. Explain the process of digestion in ruminants.
Answer:
1. Ruminants (like cows and buffaloes) quickly swallow grass without chewing and store it in a specialized part of the stomach called the rumen.
2. In the rumen, food is partially digested and is called cud.
3. Later, the cud returns to the mouth in small lumps, and the animal chews it thoroughly (a process called rumination).
4. The chewed food then enters the other chambers of the stomach and passes into the small intestine for complete digestion and nutrient absorption.
In simple words: Ruminants swallow grass fast, store it in the rumen, bring it back to chew later, and then digest it fully.

Exam Tip: Mention the term 'rumen' and 'cud' to secure full marks.

Question 14. Balance the following equations:-
(a) \(\text{Na} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2\)
(b) \(\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4\)
Answer:
(a) \(2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2\)
(b) \(\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2\)
In simple words: Adjust coefficients on both sides so that the number of atoms of each element is equal.

Exam Tip: Always check that mass is conserved by counting atoms on reactant and product sides.

Question 15. Explain how water is responsible for formation of soil.
Answer:
1. Water enters cracks and crevices in large rocks. During freezing temperatures, water expands, causing the rocks to crack further (frost wedging).
2. Flowing rainwater carries small rock particles that rub against each other and break down into finer soil grains.
3. Running water transports weathered mineral particles and deposits them to form fertile soil layers.
In simple words: Water enters rock cracks, expands when freezing, and breaks rocks down into tiny soil particles over time.

Exam Tip: Highlight the physical weathering action of water through freezing and flowing.

Question 16. Describe the eye of a cyclone.
Answer:
1. The eye is the calm, central area of a cyclone.
2. It is characterized by light winds and clear skies, contrasting sharply with the violent storm surrounding it.
3. The diameter of the eye typically ranges from 10 to 30 km.
In simple words: The eye is the quiet, clear center of the swirling storm.

Question 17. What causes tornado to be formed.
Answer:
A tornado is formed when warm, moist air meets cold, dry air, creating instability in the atmosphere. This temperature difference generates a rotating column of high-speed winds extending from thunderstorm clouds down to the ground.
In simple words: Tornadoes form when warm and cold air masses collide and create a powerful spinning vortex.

Exam Tip: Keywords are unstable atmospheric conditions and rotating funnel-shaped columns of air.

Question 18. What causes monsoon wind.
Answer:
Monsoon winds are caused by the differential heating of land and water. During summer, the landmass heats up much faster than the ocean, creating a low-pressure area over land that draws moisture-laden winds from the cooler ocean toward the land.
In simple words: Monsoons are seasonal winds caused by land heating up faster than oceans, creating pressure differences.

Question 19. What are reasons for lowering of water table in cities.
Answer:
1. Rapid urbanization and concreting of open ground, which prevents rainwater from seeping into the soil.
2. Excessive pumping of groundwater through tube wells to meet the demands of a growing urban population.
3. Deforestation and reduction of green cover.
In simple words: Concrete floors block rain from soaking in, and heavy pumping empties underground water supplies.

Exam Tip: List both reduced infiltration (concreting) and increased consumption (population).

Question 20. List four methods of conserving water.
Answer:
1. Rainwater harvesting (collecting and storing rainwater from rooftops).
2. Using drip irrigation in agriculture to minimize water wastage.
3. Fixing leaking taps and pipes promptly in households.
4. Reusing wastewater from washing clothes for cleaning floors or watering plants.
In simple words: Save water by harvesting rain, using drip irrigation, fixing leaks, and recycling wastewater.

Exam Tip: Rainwater harvesting and drip irrigation are key expected keywords.