CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma

CBSE CLASS XII

Em Waves

Q.1) Microwaves are electromagnetic waves with frequency, in the range of ( 1 mark )

(a) Micro Hertz
(b) Mega Hertz
(c) Giga Hertz
(d) Hertz

(Q.2) Infrared radiation lies adjacent to the low frequency or long wavelength end of the visible spectrum. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the: ( 1 mark )

(a) Energy it carries
(b) Momentum it transferred
(c) The way it heat up the surroundings
(d) Greenhouse effect

(Q.3) Give the formula for velocity of electromagnetic waves in free space? (H) (1mark )

(Q.4) What are microwaves? ( 1 mark )

(Q.5) Who was the first person to tell that light is an electromagnetic wave? ( 1 mark )

(Q.6) What is the source of an electromagnetic wave? ( 1 mark )

(Q.7) What is the frequency limit of visible range of electromagnetic spectrum in KHz?(1mark)

(Q.8) What is the name given to that part of electromagnetic spectrum which is used in radar? (H) ( 1 mark )

(Q.9) Which of the following has shortest wavelength? Microwaves, ultraviolet rays and X-rays. ( 1 mark )

(Q.10) What is the ratio of speed of infrared rays to ultraviolet rays in vacuum? ( 1 mark )

(Q.11) An electromagnetic wave is propagating along y-axis. What is the direction along which oscillations of magnetic field are taking place? (H) ( 1 mark )

(Q.12) Name the electromagnetic radiations used for viewing objects through haze and fog? ( 1 mark )

(Q.13) What is the frequency of electromagnetic radiation to which the human eye is most sensitive? ( 1 mark )

(Q.14) What is the role of ozone in the atmosphere? ( 1 mark )

(Q.15) What is the cut off frequency beyond which the ionosphere does not reflect electromagnetic radiations? (H) ( 1 mark )

(Q.16) What is the ratio of speed of gamma rays and radio waves in vacuum? ( 1 mark )

(Q.17) If ɛ₀ and μ₀ are the electric permittivity and magnetic permeability in vacuum, and are corresponding quantities in medium, then refractive index of the medium is: (H) ( 1 mark )

(Q.18) The energy of electromagnetic wave in vacuum is given by the relation: (H) ( 1 mark )

(Q.19) Let us consider an example of a plane electromagnetic wave propagating along z direction. The electric field E is along the x-axis and varies sinusoidally with z, at a given time. What is the direction of magnetic field ? ( 1 mark )

(a) Along x-axis
(b) Along y-axis
(c) Along z-axis
(d) Along x-y plane

(Q.20) When the sun shines on our hand, we feel the energy being absorbed from electromagnetic waves, our hands get warm but we do not feel pressure. Why ? ( 1 mark )

(a) This implies electromagnetic waves, does not carry momentum
(b) Because it carries energy only
(c) Momentum transferred is so small that we do not feel pressure
(d) Electromagnetic waves do not have any relation with pressure

(Q.21) What is average magnetic field of the air plane a distance of 100 km from a radio transmitter receiving a signal of power 10.0 micro watts/m2? (H) ( 1 mark )

(Q.22) Electric and magnetic fields oscillate sinusoidally in space and time in an electromagnetic wave. The oscillating electric and magnetic fields and are perpendicular to each other and to the direction of propagation of the electromagnetic wave. For a wave of frequency , wavelength , propagating along z direction, E0 and B0 are related as: (H) (1mark )

(Q.23) Which of the following law was modified by Maxwell by introducing Maxwell displacement current? ( 1 mark )

(a) Ampere’s law
(b) Biot savart’s law
(c) Gauss’s law
(d) Faraday’s law

(Q.24) In an electromagnetic wave, the amplitudes of magnetic field Ho and electric field Eo in free space are related as: (H) ( 1 mark )

(Q.25) Which of the following are not electromagnetic waves? ( 1 mark )

(a) Cosmic rays
(b) Gamma rays
(c) β-rays
(d) X-rays

(Q.26) For television broadcasting, the frequency emoployed is normally ( 1 mark )

(a) 30 to 300 MHz.
(b) 30 to 300 GHz.
(c) 30 to 300 KHz.
(d) 30 to 300 Hz.

(Q.27) In an apparatus, the electric field was found to oscillate with amplitude of 18 V/m. The magnitude of the oscillating magnetic field will be: ( 1 mark )

(a) 4 × 10^–6T
(b) 6 × 10^–8T
(c) 9 × 10^–9T
(d) 11 × 10^–11T

(Q.28) The missing term in Ampere’s circuital law is: ( 1 mark )

(Q.29) Which of the following term acts as a source of magnetic field in exactly the same way as conduction current? ( 1 mark )

(Q.30) In the case of steady electric fields in a conducting wire, which of the following quantity is zero ?

(a) Conduction current
(b) Magnetic current
(c) Magnetic lines of forces
(d) Displacement current

(Q.31) What is the source of electromagnetic waves? ( 1 mark )

(a) Stationary charges
(b) Charges in uniform motion
(c) Accelerated charges
(d) Varrying magnetic field

(Q.32) What is the average electric field at the airplane flying at a distance of 100 km from a radio transmitter receiving a signal of power 10.0 micro watts/m2 ? (H) ( 1 mark )

(a) 8.68 ×10^–2 V/m
(b) 6.14 ×10^–1 V/m
(c) 86.8 ×10^–2 V/m
(d) 6.14 ×10^–2 V/m

(Q.33) A parallel plate capacitor made of circular plates each of radius R = 5 cm has a capacitance C = 100 pF. The capacitor is connected to a 220 V a.c supply with angular frequency of 295 rad s^–1. What is the rms value of the conduction current ? (H) ( 1 mark )

(Q.34) The dimensions of E/B are same as that of: ( 1 mark )

(a) Acceleration
(b) Velocity
(c) Charge
(d) Current

(Q.35) In case of microwave oven, which material is used as vessels ? ( 1 mark )

(a) Metal
(b) Steel
(c) Porcelain
(d) Copper

(Q.36) The microwave oven has an advantage over conventional heating method as in microwave oven: ( 1 mark )

(a) Energy is not wasted in heating up the vessel
(b) Porcelain has been used as vessel
(c) Microwave radiation has been used as source
(d) Special vacuum tubes have been used

(Q.37) Infrared band lies adjacent to the low-frequency or long-wavelength end of the visible spectrum. Infrared waves are sometimes referred to as: ( 1 mark )

(a) Low-frequency waves
(b) Heat waves
(c) Long-wavelength waves
(d) Electromagnetic waves

(Q.38) The spectrum of electromagnetic wave stretches over an infinite range of wavelengths. Different regions are known by different names. The basic difference lies in their: (H) (1mark )

(a) Atoms or molecules
(b) Wavelengths or frequencies
(c) Electric or magnetic field
(d) Difference in frequencies with visible light

(Q.39) Electromagnetic waves are produced by
(a) an accelerating charge
(b) a static charge
(c) chargeless particle
(d) a moving charge

(Q.40) An electromagnetic wave of frequency passes from vacuum into a dielectric medium with permittivity . Then

(a) Wavelength is halved and frequency remains unchanged
(b) Wavelength is doubled and frequency becomes half
(c) Wavelength is doubled and the frequency remains unchanged
(d) Wavelength and frequency both remain unchanged.

(Q.41) Radio waves of constant amplitude can be generated with ( 1 mark )

(a) Filter
(b) Rectifier
(c) FET
(d) Oscillator

(Q.42) The area to be covered for T.V. telecast is doubled then the height of transmitting antenna will have to be ( 1 mark )

(a) Halfed
(b) Doubled
(c) Quardupled
(d) Kept unchanged

(Q.43) The electric field vector of a plane electromagnetic wave oscillates sinusoidally at a frequency of 4.5 x 10¹⁰ Hz. What is the wavelength? (H) ( 2 Marks )

(Q.44) Find the wavelength of electromagnetic waves of frequency 5x10¹⁹ Hz in free space. Give its two applications. ( 2 Marks )

(Q.45) Why is it necessary to use satellite for long distance T.V. transmission? Give reasons. ( 2 Marks )

(Q.46) Give four properties of electromagnetic waves. ( 2 Marks )

(Q.47) A plane electromagnetic wave travels, in vacuum, along the Y-direction. Write the,

(i) Ratio of the magnitudes of electric and magnetic field.
(ii) The directions of its electric and magnetic field vectors. (H) ( 2 Marks )

(Q.48) Sky waves are not used in transmitting TV signals. Why? State two factors by which the range of transmission of TV signals can be increased. ( 2 Marks )

(Q.49) Explain the following terms:

(a) Ground waves.
(b) Space waves.
(c) Sky waves. ( 3 Marks )

(Q.50) The TV transmission tower at particular station has a height of 120 m.

a) What is its covering range?
b) By how much the height of tower should be increased to double its coverage range? (3Marks )

(Q.51) What is “Greenhouse effect” for the atmosphere of earth? Write its importance. ( 3 Marks )

(Q.52) Suppose that the electric field part of an electromagnetic wave in vacuum is ={(3.1 N/C) cos [(1.8 rad/m) y + (5.4 × 10⁶ rad/s)t]} . (H)

(a) What is the direction of propagation?
(b) What is the wavelength λ ?
(c) What is the frequency ν ?
(d) What is the amplitude of the magnetic field part of the wave?
(e) Write an expression for the magnetic field part of the wave. ( 5 Marks )

(Q.53) Suppose that the electric field part of an electromagnetic wave in vacuum is Ê= {(3.1 N/C) cos [(1.8 rad/m) y + (5.4 × 10⁶ rad/s)t]} Î . (H)

(a) What is the direction of propogation?
(b) What is the wavelength λ ?
(c) What is the frequency ν ?
(d) What is the amplitude of the magnetic field part of the wave?
(e) Write an expression for the magnetic field part of the wave.

Submitted By Mr. Ajay Sharma
Email Id : [email protected]