Electromagnetic Waves · Question 18

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 :

1. 12 103 J
2. 24 103 J
3. 48 103 J
4. 10 103 J

Which colour of the light has the longest wavelength?

1. blue
2. violet
3. red
4. green

A parallel plate capacitor of capacitance 20 is being charged by a voltage source whose potential is changing at the rate of 3 V/s. The conduction current through the connecting wires, and the displacement current through the plates of the capacitor, would be, respectively :

1. zero, zero
2. zero, 60
3. 60 , 60
4. 60 , zero

An EM wave is propagating in a medium with a velocity v = v i. The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along

1. −z direction
2. +z direction
3. −y direction
4. −x direction

In an electromagnetic wave in free space the root mean square value of the electric field is Erms = 6 V m-1. The peak value of the magnetic field is

1. 2.83 10-8 T
2. 0.70 10-8 T
3. 4.23 10-8 T
4. 1.41 10-8 T

Out of the following options which one can be used to produce a propagating electromagnetic wave?

1. A chargeless particle
2. An accelerating charge
3. A charge moving at constant velocity
4. A stationary charge

A 100 resistance and a capacitor of 100 reactance are connected in series across a 220 V source. When the capacitor is 50\% charged, the peak value of the displacement current is

1. 2.2 A
2. 11 A
3. 4.4 A
4. 11 2 A

The energy of the em waves is of the order of 15 keV. To which part of the spectrum does it belong ?

1. Ultraviolet rays
2. -rays
3. X-rays
4. Infra-red rays

A radiation of energy 'E' falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (C = Velocity of light)

1. 2EC2
2. EC2
3. EC
4. 2EC

Light with an energy flux of 25 104 W m-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

1. 1.25 10-6 N
2. 2.50 10-6 N
3. 1.20 10-6 N
4. 3.0 10-6 N