CBSE Class 12 Physics Electromagnetic Waves Assignment Set A

 

 Important Questions for NCERT Class 12 Physics Electromagnetic Waves

 

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

Question. If e0 and m0 are the electric permittivity and magnetic permeability in a free space, e and m are the  corresponding quantities in medium, the index of refraction of the medium is  
(a) √(ε₀μ₀ /εμ)
(b) √(εμ /ε₀μ₀₎
(c) √(ε₀μ /εμ₀₎
(d) √ε/ε₀

Answer: B

Question. The velocity of electromagnetic radiation in a medium of permittivity e0 and permeability m0 is given by   
(a) 1/√μ₀ε₀
(b) 1/√μ₀/ε₀
(c) ε₀ /μ₀
(d) √μ₀/ε₀

Answer: A

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 of the following are not electromagnetic waves?
(a) cosmic rays
(b) γ-rays
(c) β-rays
(d) X-rays.

Answer: C

Question. The energy of electromagnetic wave in vacuum is given by the relation 

Answer: D

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

Answer: D

Question. Which of the following radiations has the least wavelength ?
(a) γ -rays
(b) β -rays
(c) α -rays
(d) X -rays

Answer: A

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

Answer: B

Question. Radio waves diffract around building although light waves do not. The reason is that radio waves
(a) travel with speed larger than c
(b) have much larger wavelength than light
(c) are not electromagnetic waves
(d) None of these

Answer: B

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. Intensity of electromagnetic wave will be
(a) I = cμ₀B₀²/2
(b) I = cε₀B₀²/2
(c) I = B₀²/cμ₀
(d) I = E₀²/2cε0

Answer: B

Question. An electromagnetic wave is propagating along Y-axis. Then
(a) oscillating electric field is along X-axis and oscillating magnetic field is along Y-axis
(b) oscillating electric field is along Z-axis and oscillating magnetic field is along X-axis
(c) both oscillating electric and magnetic fields are along Y-axis, but phase difference between them is 90°
(d) both oscillating electric and magnetic fields are mutually perpendicular in arbitrary direction

Answer: B

Question. The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to
(a) the speed of light in vacuum
(b) reciprocal of speed of light in vacuum
(c) the ratio of magnetic permeability to the electric susceptibility of vacuum
(d) unity

Answer: B

Question. An EM wave radiates outwards from a dipole antenna, with E₀ as the amplitude of its electric field vector. The electric field E₀ which transports significant energy from the source falls off as
(a) 1/r3
(b) 1/r2
(c) 1/r 
(d) remains constant

Answer: C

Question. An electromagnetic wave travels in vacuum along z-direction E = (E₁î + E₂ĵ) cos (kz -ωt) . Choose the correct options from the following
(a) The associated magnetic field is given as B = 1/c (E₁î + E₂ĵ) cos (kz -ωt)
(b) The associated magnetic field is given as B = 1/c (E₁î + E₂ĵ) cos (kz -ωt)
(c) The given electromagnetic field is circularly polarised
(d) The given electromagnetic wave is plane polarised

Answer: D

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

Answer: C

Question. Light with an energy flux of 25 × 10⁴ Wm^–2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm², the average force exerted on the surface is :
(a) 1.25 × 10^–6 N
(b) 2.50 × 10^–6 N
(c) 1.20 × 10^–6 N
(d) 3.0 × 10^–6 N

Answer: B

Question. Pick out the longest wavelength from the following types of radiation.
(a) blue light
(b) gamma rays
(c) X-rays
(d) red light

Answer: D

Question. One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in
(a) visible region
(b) infrared region
(c) ultraviolet region
(d) microwave region

Answer: C

Question. The electric and the magnetic field associated with an E.M. wave, propagating along the +z-axis, can be represented by 

Answer: A

DIRECTIONS for Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer from the following-
(a) Statement -1 is false, Statement-2 is true
(b) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(d) Statement -1 is true, Statement-2 is false

Question. Statement 1 : Environmental damage has increased the amount of ozone in the atmosphere.
Statement 2 : Increase of ozone increases the amount of ultraviolet radiation on earth.

Answer: A

Question. Statement 1 : Radio waves can be polarised.
Statement 2 : Sound waves in air are longitudinal in nature.

Answer: C

Question. Statement 1 : The earth without atmosphere would be inhospitably cold.
Statement 2 : All heat would escape in the absence of atmosphere.

Answer: B

Question. Statement 1 : When variable frequency a.c. source is connected to a capacitor, displacement current increases with increase in frequency.
Statement 2 : As frequency increases conduction current also increases.

Answer: B

Question. Statement 1 : Television signals are received through skywave propagation.
Statement 2 : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

Answer: A

Question. Statement 1 : Ultraviolet radiations of higher frequency waves are dangerous to human being.
Statement 2 : Ultraviolet radiation are absorbed by the atmosphere.

Answer: C

Question. Statement 1 : Short wave bands are used for transmission of radio waves to a large distance.
Statement 2 : Short waves re reflected by ionosphere.

Answer: A