Electromagnetic Waves

A point light source emits E.M. waves in free space. A detector, placed at a distance of L m, measures the intensity as I0. The detector is now shifted to another location on the same spherical surface ensuring the angle between original location and new location as 45°. The measured intensity at new location will be .

1. I04
2. I0
3. I0 2
4. I02

For an electromagnetic wave propagating through vacuum, k, E and represent propagation vector, electric field and angular frequency, respectively. The magnetic field associated with this wave is represented by :

1. E k
2. k E
3. ( E k )
4. ( k E )

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the correct answer from the options given below :

1. Both (A) and (R) are true and (R) is the correct explanation of (A)
2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
3. (A) is true but (R) is false
4. (A) is false but (R) is true

A magnetic field vector in an electromagnetic wave is represented by B=B0 (2 t- 2 x ) j. Its associated electric field vector is .

1. E=- B0 (2 t- 2 x ) k
2. E=- B0 (2 t- 2 x ) i
3. E= B0 (2 t- 2 x ) k
4. E= B0 (2 t- 2 x ) i

An electromagnetic wave travelling in x-direction is described by field equation Ey=300 (t- xc ). If the electron is restricted to move in y-direction only with speed of 1.5 106 m/s then ratio of maximum electric and magnetic forces acting on the electron is .

1. 200
2. 150
3. 400
4. 300

An electromagnetic wave travels in free space along the x-direction. At a particular point in space and time, B=2 10-7 j T is associated with this wave. The value of corresponding electric field E at this point is V/m.

1. 60 k
2. -60 k
3. 30 k
4. -600 k

The electric field of an electromagnetic wave travelling through a medium is given by E(x, t) = 25 (2.0 1015 t - 107 x ) n then the refractive index of the medium is . (All given measurements are in SI units)

1. 2
2. 1.2
3. 1.5
4. 1.7

A plane electromagnetic wave is moving in free space with velocity c = 3 108 m/s and its electric field is given as E = 54 (kz - t) j V/m, where j is the unit vector along y-axis. The magnetic field vector B of the wave is :

1. -1.8 10-7 (kz - t) i T
2. +1.8 10-7 (kz - t) i T
3. 1.4 10-7 (kz - t) k T
4. 1.4 10-7 (kz - t) i T

A point source is kept at the center of a spherically enclosed detector. If the volume of the detector is increased by 8 times, the intensity will

1. increase by 64 times
2. decrease by 4 times
3. decrease by 8 times
4. increase by 8 times

The equation of the electric field of an electromagnetic wave propagating through free space is given by : E = 377 (6.27 103 t - 2.09 10-5 x) N/C The average intensity of the electromagnetic wave is ( 1 ) W/m2. The value of α is . (Take 0 0 = 377 in SI units )

The ratio of speeds of electromagnetic waves in vacuum and a medium, having dielectric constant k = 3 and permeability of = 2 0, is ( 0 = permeability of vacuum)

1. 6 : 1
2. 3 : 2
3. 6 : 1
4. 36 : 1

The electric field of a plane electromagnetic wave, travelling in an unknown nonmagnetic medium is given by, Ey = 20 (3 106 x - 4.5 1014 t ) V/m (where x, t and other values have S.I. units). The dielectric constant of the medium is (speed of light in free space is 3 108 m/s)

A laser beam has intensity of 4.0 1014 W/m2. The amplitude of magnetic field associated with beam is T. (Take 0 = 8.85 10-12 C2/Nm2 and c = 3 108 m/s)

1. 1.83
2. 2.0
3. 5.5
4. 18.3

The electric field in a plane electromagnetic wave is given by : Ey = 69 [0.6 103x - 1.8 1011t ] V/m. The expression for magnetic field associated with this electromagnetic wave is T.

1. Bz = 2.3 10-7 [0.6 103x - 1.8 1011t ]
2. Bz = 2.3 10-7 [0.6 103x + 1.8 1011t ]
3. By = 2.3 10-7 [0.6 103x - 1.8 1011t ]
4. By = 69 [0.6 103x + 1.8 1011t ]

The unit of 2I 0 c is : (I = intensity of an electromagnetic wave, c = speed of light)

1. Vm
2. NC-1
3. NC
4. Nm

If an optical medium possesses a relative permeability of 10 and relative permittivity of 10.0885, then the velocity of light is greater in vacuum than that in this medium by times. ( 0 = 4 10-7 H/m, 0 = 8.85 10-12 F/m, c = 3 108 m/s)

The radiation pressure exerted by a 450 W light source on a perfectly reflecting surface placed 2 m away from it, is

1. 3 10-8 Pascals
2. 0
3. 1.5 10-8 Pascals
4. 6 10-8 Pascals

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the most appropriate answer from the options given below :

1. Both (A) and (R) are true and (R) is the correct explanation of (A)
2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
3. (A) is false but (R) is true
4. (A) is true but (R) is false

A plane electromagnetic wave propagates along the + x direction in free space. The components of the electric field, E and magnetic field, B vectors associated with the wave in Cartesian frame are

1. Ex, By
2. Ey, Bx
3. Ey, Bz
4. Ez, By

Due to presence of an em-wave whose electric component is given by E = 100 ( t - kx) NC-1 a cylinder of length 200 cm holds certain amount of em-energy inside it. If another cylinder of same length but half diameter than previous one holds same amount of em-energy, the magnitude of the electric field of the corresponding em-wave should be modified as

1. 50 ( t - kx) NC-1
2. 400 ( t - kx) NC-1
3. 200 ( t - kx) NC-1
4. 25 ( t - kx) NC-1

The magnetic field of an E.M. wave is given by B = ( 32 i + 12 j )30 [ (t - zc ) ] (S.I. Units). The corresponding electric field in S.I. units is:

1. E = ( 12 i + 32 j )30c [ (t + zc ) ]
2. E = ( 12 i - 32 j )30c [ (t - zc ) ]
3. E = ( 32 i - 12 j )30c [ (t + zc ) ]
4. E = ( 34 i + 14 j )30c [ (t - zc ) ]

The electric field of an electromagnetic wave in free space is E=57 [7.5 106t-5 10-3(3x+4y) ](4 i-3 j) N/C. The associated magnetic field in Tesla is

1. B= 573 108 [7.5 106t-5 10-3(3x+4y) ]( k)
2. B= 573 108 [7.5 106t-5 10-3(3x+4y) ](5 k)
3. B=- 573 108 [7.5 106t-5 10-3(3x+4y) ]( k)
4. B=- 573 108 [7.5 106t-5 10-3(3x+4y) ](5 k)

A plane electromagnetic wave of frequency 20 MHz travels in free space along the +x direction. At a particular point in space and time, the electric field vector of the wave is Ey=9.3 V m-1. Then, the magnetic field vector of the wave at that point is

1. Bz=1.55 10-8 T
2. Bz=6.2 10-8 T
3. Bz=3.1 10-8 T
4. Bz=9.3 10-8 T