Electromagnetic Waves — Class 12 Physics PYQs

The given diagram exhibits the relationship between the wavelength of the electromagnetic waves and the energy of photon associated with them. The three points P, Q and R marked on the diagram may correspond respectively to :
(A) X-rays, microwaves, UV radiation
(B) X-rays, UV radiation, microwaves
(C) UV radiation, microwaves, X-rays
(D) Microwaves, UV radiation, X-rays

X-rays are more harmful to human beings than ultraviolet radiations because X-rays -
(A) have frequency lower than that of ultraviolet radiations.
(B) have wavelength smaller than that of ultraviolet radiations.
(C) move faster than ultraviolet radiations in air.
(D) are mechanical waves but ultraviolet radiations are electro-magnetic waves.

Assertion (A) : Out of Infrared and radio waves, the radio waves show more diffraction effect.
Reason (R) : Radio waves have greater frequency than infrared waves.

A parallel plate capacitor is charged by an ac source. Show that the sum of conduction current ($I_c$) and the displacement current ($I_d$) has the same value at all points of the circuit.
(b) In case (a) above, is Kirchhoff's first rule (junction rule) valid at each plate of the capacitor ? Explain.

How is an electromagnetic wave produced ?
(b) An electromagnetic wave is travelling in vertically upward direction. At an instant, its electric field vector points in west direction. In which direction does the magnetic field vector point at that instant ?
(c) Estimate the ratio of shortest wave length of radio waves to the longest wave length of gamma waves.

The electric field $\vec{E}$ of an electromagnetic wave propagating in north direction is oscillating in up and down direction. Describe the direction of magnetic field $\vec{B}$ of the wave.
(b) Are the wave length of radio waves and microwaves longer or shorter than those detectable by human eyes ?
(c) Write main use of each of the following in human life :
(i) Infrared waves (ii) Gamma rays

Electromagnetic waves with wavelength 10 nm are called :
(A) Infrared waves
(B) Ultraviolet rays
(C) Gamma rays
(D) X-rays

Welders wear special glass goggles or face masks with glass windows to protect their eyes from radiations produced by welding arcs. These radiations are :
(A) X-rays
(B) Ultraviolet rays
(C) Infrared waves
(D) Gamma rays

In four regions I, II, III and IV, the magnetic field is given by :
I. B${}_y$ = B${}_0$ sin kz
II. B${}_y$ = B${}_0$ cos kz
III. B${}_y$ = B${}_0$ sin (kz – $\omega$t)
IV. B${}_y$ = B${}_0$ sin kz + B${}_0$ cos kz
The electromagnetic wave will exist in the region :
(A) IV
(B) I
(C) III
(D) II

In the four regions, I, II, III and IV, the electric fields are described as :
Region I : E${}_x$ = E${}_0$ sin (kz – $\omega$t)
Region II : E${}_x$ = E${}_0$
Region III : E${}_x$ = E${}_0$ sin kz
Region IV : E${}_x$ = E${}_0$ cos kz
The displacement current will exist in the region :
(A) I
(B) IV
(C) II
(D) III