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To which part of the electromagnetic spectrum does a wave of frequency 5 × 1019 Hz belong?
The wave of frequency 5 × 1019 Hz corresponds to X-rays or γ-region of the em
spectrum.
How are microwaves produced ?
Microwaves are produced by special vacuum tubes like klystrons, magnetrons and gunn
diodes.
Which part of electromagnetic spectrum has largest penetrating power?
γ-rays.
A capacitor has been charged by a dc source. What are the magnitudes of conduction and
displacement currents, when it is fully charged?
Conduction current and displacement current both are zero.
Which part of electromagnetic spectrum is absorbed from sunlight by ozone layer ?
Ultraviolet rays.
Welders wear special goggles or face masks with glass windows to protect their eyes from
electromagnetic radiations. Name the radiations and write the range of their frequency.
Ultraviolet rays (UV rays)
The frequency range of UV rays is 0.75 × 1015 Hz to 0.5 × 1018 Hz.
Name the electromagnetic waves, which (i) maintain the Earth’s warmth, and (ii) are used in
aircraft navigation.
(i) Infrared (ii) Microwaves
Arrange the following electromagnetic waves in order of increasing frequency: γ-rays,
microwaves, infrared rays and ultraviolet rays.
γ-rays > ultraviolet rays > infrared rays > microwaves.
Name em radiations used for detecting fake currency notes.
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UV radiation.
Let the wavelengths of the electromagnetic waves used quite often for
(i) killing germs in household water purifiers, (ii) remote sensing
(iii) treatment of cancer, be labelled as λ1, λ2 and λ3 in increasing order.
(i) UV radiation (λ1), (ii) Microwaves (λ2), (iii) γ-rays (λ3)
The increasing order of wavelength is λ3 < λ1 < λ2.
Is the ratio of frequencies of ultraviolet rays and infrared rays in glass more than, less than or
equal to 1?
More than 1, because the frequency of ultraviolet rays is greater than that of infrared
rays.
For which frequency of light, the human eye is most sensitive?
Human eye is sensitive to the light of wavelength, λ = 555 nm. So, its frequency is
The velocity of propagation (in vacuum) and the frequency of (i) X-rays and (ii) radiowaves are
denoted by (vx, nx) and (vR, nR) respectively.
How do the values of : (a) vX and vR (b) nX and nR, compare with each other?
(a) vX = vR (b) nX > nR
Which of the following, if any, can act as a source of electromagnetic waves?
(i) A charge moving with a constant velocity.
(ii) A charge moving in a circular orbit.
(iii) A charge at rest.
(ii) A charge moving in a circular orbit.
What is the phase difference between electric and magnetic field vectors in an em wave?
Zero
Arrange the following electromagnetic waves in decreasing order of wavelength: γ-rays, infrared
rays, X-rays and microwaves.
Microwaves > infrared > X-rays > γ-rays.
The current in a circuit containing a capacitor is 0.15 A. What is the displacement current and
where does it exist?
As conventional current is equal to displacement current. It is also 0.15 A and exists
across the capacitor plates.
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Out of microwaves, ultraviolet rays and infrared rays, which radiation will be most effective for
emission of electrons from a metallic surface?
Ultraviolet rays will be most effective for emission of electrons because these rays have
the highest frequency and hence more energetic.
A linearly polarized electromagnetic wave given as E = cos (kz – ωt) is incident normally on
a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive,
the reflected wave will be given as
(a) Er = – cos(kz – ωt).
(b) Er = cos(kz + ωt).
(c) Er = – cos(kz + ωt).
(d) Er = sin(kz – ωt).
(b)
If E and B represent electric and magnetic field vectors of the electromagnetic wave, the
direction of propagation of electromagnetic wave is along
(a) E.
(b) B.
(c) B × E.
(d) E × B.
(d)
A plane electromagnetic wave propagating along x direction can have the following pairs of E
and B
(a) Ex, By. (b) Ey, Bz.
(c) Bx, Ey. (d) None of these
(b)
The source of electromagnetic waves can be a charge
(a) moving with a constant velocity.
(b) moving in a circular orbit.
(c) at rest.
(d) falling in a magnetic field.
(b)
The structure of solids is investigated by using
(a) cosmic rays (b) X-rays
(c) γ-rays (d) infrared rays
(b) X-rays are used to investigate structure of solids.
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(a) Wave vector, k =
A radiation of energy ‘E’ falls normally on a perfectly reflecting surface. The momentum
transferred to the surface is
(a) when radiation is totally reflected, momentum transferred is 2P =
