CBSE Class 12 Physics Electromagnetic Waves Worksheet Set B

Important Questions for NCERT Class 12 Physics Electromagnetic Waves

Question. The energy of the em waves is of the order of 15 keV.To which part of the spectrum does it belong?
(a) Ultraviolet rays
(b) g-rays
(c) X-rays
(d) Infra-red rays

Answer: C

Question. The condition under which a microwave oven heats up a food item containing water molecules most efficiently is
(a) microwaves are heat waves, so always produce heating
(b) infra-red waves produce heating in a microwave oven
(c) the frequency of the microwaves must match the resonant frequency of the water molecules
(d) the frequency of the microwaves has no relation with natural frequency of water molecules.

Answer: C

Question. Frequency of infrared wave is approximately:
(a) 1018 Hz
(b) 1014 Hz 
(c) 109 Hz
(d) 1016 Hz

Answer: B

Question. The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is
(a) microwave, infrared, ultraviolet, gamma rays
(b) gamma rays, ultraviolet, infrared, microwaves
(c) microwaves, gamma rays, infrared, ultraviolet
(d) infrared, microwave, ultraviolet, gamma rays

Answer: A

Question. If lv, lx and lm represent the wavelengths of visible light, X-rays and microwaves respectively, then
(a) lm > lx > lv
(b) lm > lv > lx
(c) lv > lx > lm
(d) lv > lm > lx. 

Answer: B

Question. We consider the radiation emitted by the human body. Which one of the following statements is true?
(a) The radiation emitted is in the infrared region.
(b) The radiation is emitted only during the day.
(c) The radiation is emitted during the summers and absorbed during the winters.
(d) The radiation emitted lies in the ultraviolet region and hence is not visible. 

Answer: A

Question. Which of the following rays are not electromagnetic waves ?
(a) X-rays
(b) g-rays
(c) b-rays
(d) heat rays 

Answer: C

Question. Which of the following statement is false for the properties of electromagnetic waves ?   
(a) Both electric and magnetic field vectors attain the maxim and minima at the same place and same time.
(b) The energy in electromagnetic wave is divided equally between electric and magnetic vectors.
(c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.
(d) These waves do not require any material medium for propagation 

Answer: C

Question. Biological importance of ozone layer is   
(a) it stops ultraviolet rays
(b) ozone layer reduces green house effect
(c) ozone layer reflects radio waves
(d) ozone layer controls O2/H2 ratio in atmosphere.

Answer:  A

Question. Which of the following are not electromagnetic waves?    
(a) cosmic rays
(b) g-rays
(c) b-rays
(d) X-rays

Answer: C

Question. The frequency modulated waves are
(a) reflected by atmosphere
(b) absorbed by atmosphere
(c) bend by atmosphere
(d) radiowaves

Answer: C

Question. An electromagnetic wave going through vacuum is described by E = E₀ sin(kx – ωt); B = B₀ sin (kx – ωt). Which of the following equations is true?
(a) E₀k = B₀ω
(b) E₀ω = B₀k
(c) E₀B₀ = ωk
(d) None of these

Answer: A

Question. The ozone layer absorbs radiation of wavelengths
(a) less than 3 × 10^–7 m
(b) more than 3 × 10^–7 m
(c) less than 3 × 10^–5 m
(d) more than 3 × 10^–5 m

Answer: A

Question. An electromagnetic wave of frequency n = 3.0 MHz passes from vacuum into a dielectric medium with permittivity Î= 4.0 . Then
(a) wavelength is halved and frequency remainsunchanged 
(b) wavelength is doubled and frequency becomes half
(c) wavelength is doubled and the frequency remains unchanged
(d) wavelength and frequency both remain unchanged

Answer: A

Question. 10 cm is a wavelength corresponding to the spectrum of
(a) infrared rays
(b) ultra-violet rays
(c) microwaves
(d) γ -rays

Answer: C

Question. Approximate height of ozone layer above the ground is
(a) 60 to 70 km
(b) 59 km to 80 km
(c) 70 km to 100 km
(d) 100 km to 200 km

Answer: A

Question. In an electromagnetic wave
(a) power is transmitted along the magnetic field
(b) power is transmitted along the electric field
(c) power is equally transferred along the electric and magnetic fields
(d) power is transmitted in a direction perpendicular to both the fields

Answer: D

Question. An electromagnetic wave passes through space and its equation is given by E = E₀ sin (ωt – kx) where E is electric field. Energy density of electromagnetic wave in space is
(a) 1/2 ε₀E₀²
(b) 1/4 ε₀E₀²
(c) ε₀E₀²
(d) 2ε₀E₀²

Answer: A

Question. The ionosphere
(a) reflects back radiowaves in the AM band
(b) reflects back radiowaves in the FM band
(c) absorbs radiowaves in the AM band
(d) absorbs radiowaves in the FM band

Answer: A

Question. The frequency 2 MHz belongs to
(a) visible light
(b) X-rays
(c) microwaves
(d) radiowaves

Answer: D

Question. Radio waves and visible light in vacuum have
(a) same velocity but different wavelength
(b) continuous emission spectrum
(c) band absorption spectrum
(d) line emission spectrum

Answer: A

Question. 10 cm is a wavelength corresponding to the spectrum of
(a) infrared rays
(b) ultra-violet rays
(c) microwaves
(d) γ -rays

Answer: C

Question. An electromagnetic wave, going through vacuum is described by E = E₀ sin(kx -ωt) . Which of the following is independent of wavelength ?
(a) k
(b) ω
(c) k/ω
(d) kω

Answer: C

Question. In a plane electromagnetic wave propagating in space has an electric field of amplitude 9 × 10³ V/m, then the amplitude of the magnetic field is
(a) 2.7 × 10¹² T
(b) 9.0 × 10^–3 T
(c) 3.0 × 10^–4 T
(d) 3.0 × 10^–5 T

Answer: D

Question. Light with an energy flux of 20 W/cm² falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 min is
(a) 36 × 10^–5 kg-m/s
(b) 36 × 10^–4 kg-m/s
(c) 108 × 10⁴ kg-m/s
(d) 1.08 × 10⁷ kg-m/s

Answer: B

Question. The electromagnetic waves travel with a velocity
(a) equal to velocity of sound
(b) equal to velocity of light
(c) less than velocity of light
(d) None of these

Answer: B

Question. Electromagnetic waves are transverse in nature is evident by
(a) polarization
(b) interference
(c) reflection
(d) diffraction

Answer: A

Question. The speed of electromagnetic wave in vacuum depends upon the source of radiation. It
(a) increases as we move from g-rays to radio waves
(b) decreases as we move from g-rays to radio waves
(c) is same for all of them
(d) None of these

Answer: C

Question. The electric and magnetic field of an electromagnetic wave are in
(a) phase and parallel to each other
(b) opposite phase and perpendicular to each other
(c) opposite phase and parallel to each other
(d) phase and perpendicular to each other

Answer: D

Question. If ε₀ and μ₀ are the electric permittivity and magnetic permeability in vacuum, ε and μ are corresponding quantities in medium, then refractive index of the medium is
(a) √ε/ε₀
(b) √ε₀μ/εμ₀
(c) √ε₀μ₀/εμ
(d) √εμ/ε₀μ₀

Answer: D

Important Questions for NCERT Class 12 Physics Electromagnetic Waves

Question. What is the cause of Green house effect?
(a) Infra-red rays
(b) Ultra violet rays
(c) X-rays
(d) Radio waves 

Answer: A

Question. Which wavelength of sun is used finally as electric energy? 
(a) Radio waves
(b) Infra red waves
(c) Visible light
(d) Micro waves

Answer: B

Question. Biological importance of ozone layer is
(a) it stops ultraviolet rays
(b) ozone layer reduces green house effect
(c) ozone layer reflects radio waves
(d) ozone layer controls O2/H2 ratio in atmosphere.

Answer: A

Question. The frequency order for g-rays (B), X-rays (A),UV rays (C) is
(a) B > A > C
(b) A > B > C
(c) C > B > A
(d) A > C > B. 

Answer: A

Question. Ozone layer blocks the radiations of wavelength
(a) more than 3 × 10–7 m
(b) equal to 3 × 10–7 m
(c) less than 3 × 10–7 m
(d) all of these 

Answer: D

Question. Which of the following electromagnetic radiations have the smaller wavelength?
(a) X-rays
(b) g-rays
(c) UV waves
(d) microwaves

Answer: B

Question. A signal emitted by an antenna from a certain point can be received at another point of the surface in the form of
(a) sky wave
(b) ground wave
(c) sea wave
(d) both (a) and (b)

Answer: D

Question. The structure of solids is investigated by using
(a) cosmic rays
(b) X-rays
(c) g-rays
(d) infra-red radiations

Answer: B

Question. Which of the following electromagnetic radiations have the longest wavelength ?
(a) X-rays
(b) g-rays
(c) Microwaves
(d) Radiowaves

Answer: D

Question. Light wave is travelling along y-direction. If the corresponding E vector at any time is along the x-axis, the direction of B vector at that time is along   
(a) y-axis
(b) x-axis
(c) + z-axis
(d) – z-axis

Answer: C

Question. A 100 W resistance and a capacitor of 100 W reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is   
(a) 2.2 A
(b) 11 A
(c) 4.4 A
(d) 11 2 A 

Answer: A

Question. Light with an average flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence having surface area 20 cm2. The energy received by the surface during time span of 1 minute is   
(a) 10 × 10³ J
(b) 12 × 10³ J
(c) 24 × 10³ J
(d) 48 × 10³ J

Answer: C

Question. Electromagnetic wave consists of periodically oscillating electric and magnetic vectors   
(a) in mutually perpendicular planes but vibrating with a phase difference of π
(b) in mutually perpendicular planes but vibrating with a phase difference of π/2
(c) in randomly oriented planes but vibrating in phase
(d) in mutually perpendicular planes but vibrating in phase

Answer: D
 

Question. A wave is propagating in a medium of electric dielectric constant 2 and relative magnetic permeability 50. The wave impedance of such a medium is
(a) 5Ω
(b) 376.6 Ω
(c) 1883 Ω
(d) 3776 Ω

Answer: C

Question. The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is
(a) E/2
(b) 2E
(c) E/√2
(d) √2E

Answer: C

Question. All components of the electromagnetic spectrum in vacuum have the same
(a) energy
(b) velocity
(c) wavelength
(d) frequency

Answer: B

Question. A plane electromagnetic wave is incident on a plane surface of area A, normally and is perfectly reflected. If energy E strikes the surface in time t then average pressure exerted on the surface is (c = speed of light)
(a) zero
(b) E/Atc
(c) 2E/Atc
(d) E/c

Answer: C

Question. If a source is transmitting electromagnetic wave of frequency 8.2 × 10⁶ Hz, then wavelength of the electromagnetic waves transmitted from the source will be
(a) 36.6 m
(b) 40.5 m
(c) 42.3 m
(d) 50.9 m

Answer: A

Question. In an apparatus, the electric field was found to oscillate with an amplitude of 18 V/m. The magnitude of the oscillating magnetic field will be
(a) 4 × 10^–6 T
(b) 6 × 10^–8 T
(c) 9 × 10^–9 T
(d) 11 × 10^–11 T

Answer: B

Question. The electromagnetic radiation used in food processing sterilizing agent is
(a) microwaves
(b) UV rays
(c) gamma rays
(d) radio waves

Answer: B

Question. The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is
(a) c : 1
(b) c² : 1
(c) 1 : 1
(d) √c :1

Answer: C

Question. A plane electromagnetic wave is incident on a material surface. If the wave delivers momentum p and energy E, then
(a) p = 0, E = 0
(b) p ≠ 0, E ≠ 0
(c) p ≠ 0, E = 0
(d) p = 0, E ≠ 0

Answer: B

Question. The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is
(a) microwave, infrared, ultraviolet, gamma rays
(b) gamma rays, ultraviolet, infrared, micro-waves
(c) microwaves, gamma rays, infrared, ultraviolet
(d) infrared, microwave, ultraviolet, gamma rays

Answer: A

Question. The wave impendance of free space is
(a) zero
(b) 376.6 Ω
(c) 33.66Ω
(d) 3.76 Ω

Answer: B

Question. If λ =1´10⁴ Å then it corresponds to
(a) infrared
(b) microwaves
(c) ultraviolet
(d) X-rays

Answer: A

Question. The frequency of electromagnetic wave, which best suited to observe a particle of radii 3 × 10^–4 cm is of the order of
(a) 10¹⁵
(b) 10¹⁴
(c) 10¹³
(d) 10¹²

Answer: A

Question. If λ_v ,λ_r and λ_m represent the wavelength of visible light x-rays and microwaves respectively, then
(a) λ_m > λ_x > λ_v
(b) λ_v > λ_m > λ_y
(c) λ_m > λ_v > λ_x
(d) λ_v > λ_x > λm

Answer: C

Question. Maxwell in his famous equation of electromagnetism introduced the concept of
(a) a.c. current
(b) d.c. current
(c) displacement current
(d) impedance

Answer: C

Question. The relation between electric field E and magnetic field H in an electromagnetic wave is
(a) E = H
(b) E = μ₀/ε₀ H
(c) E = √μ₀/ε₀ H
(d) E = √ε₀/μ₀ H

Answer: C

Question. If λ = 10Å then it corresponds to
(a) infrared
(b) microwaves
(c) ultraviolet
(d) X-rays

Answer: D

Question. In an electromagnetic wave
(a) power is transmitted along the magnetic field
(b) power is transmitted along the electric field
(c) power is equally transferred along the electric and magnetic fields
(d) power is transmitted in a direction perpendicular to both the fields

Answer: D

Question. It is possible to take pictures of those objects which are not fully visible to the eye using camera films sensitive to
(a) ultraviolet rays
(b) infrared rays
(c) microwaves
(d) radiowaves

Answer: B

Question. The frequencies of X-rays, g-rays and ultraviolet rays are respectively a, b and c then
(a) a < b, b > c
(b) a > b, b > c
(c) a > b, b < c
(d) a < b, b < c

Answer: A

4. Green light of mercury has a wavelength 5.5 x 10 ^-5 cm. (a) What is the freq in MHz and period in μ s in vacuum?
(a) What is the wavelength in glass, if refractive index of glass is 1.5?
Answer: (a) ν= 5.45 x 10 ⁸ MHz; T = 1.8 x 10 ^-9 μ s (b) 3.6 x 10 ^-7 m

5. Electromagnetic waves travel in a medium with a speed of 2 x 10 8 m/s. The relative permeability of the medium is 1. Find the relative permeability.
Answer: Er = 2.25

6. In a plane electromagnetic wave, the electric field oscillates sinusoidal at a frequency of 2 x 10 10Hz and amplitude 48 Vm -1
(i) What is the wavelength of the wave?
Answer: 1.5 x 10 ^-2 m
(ii) Amplitude of the oscillating mag field.
Answer: Bo = 1.6 x 10 ^-7 T
(iii) Total average energy density of the electromagnetic field of the wave.
Answer: U = 1 x 10 ^-8 Jm -3

7. Give the ratio of velocities of two light waves traveling in vacuum having wavelengths 4000 Å & 8000 Å.
Answer: 1

8. Name the constituent radiation of electromagnetic spectrum which
(a) is used in satellite communication
(b) is used for studying crystal structure
(c) is similar to the radiation emitted during decay of radioactive nuclei
(d) has its wavelength range b/w 390 nm & 770 nm
(e) is absorbed from sunlight by ozone layer
(f) produces intense heating effect

9. A plane electromagnetic wave of freq 25 MHz travels in free space along x – direction. At a particular point in space & time, E¯ = 6.3 jv/m. Determine B¯ at this point.
Answer: B¯ = 2.1 x 10 ^-8 kˆ T

10. A parallel plate capacitor figure made of circular plates each of radius R = 6 cm has a capacitance C = 100 pF.
The capacitor is connected to a 230 V a.c. supply with angular freq of 300 rad s -1.
(a) What is the rms value of conduction current?
(b) Is the conduction current equal to the displacement current?
(c) Determine the amplitude of B at a pt 3.0 cm from the axis between the plates
Answer: (a) I = 9 μ A;
(c) d = 1 mm

11. About 5% of the power of a 100W light bulb is converted to visible radiation. What is the average intensity of visible radiation?
(a) At a distance of 1m from the bulb?
Answer: I = 0.4 W/m2
(b) At a distance of 10m Ans: I = 0.004 W/m 2