Electromagnetic Waves

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

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

1. Microwaves are heat waves, so always produce heating.
2. Infra-red waves produce heating in a microwave oven.
3. The frequency of the microwaves must match the resonant frequency of the water molecules.
4. The frequency of the microwaves has no relation with natural frequency of water molecules.