A Complete Resource Book in Physics for JEE Main

Sanjeev Kumar

Chapter 17

Electromagnetic Waves - all with Video Answers

Educators

Chapter Questions

Problem 1

If $E$ and $B$ are the electric and magnetic field vectors of electromagnetic waves then the direction of propagation of electromagnetic wave is along the direction of
(A) $\vec{E}$
(B) $\vec{B}$
(C) $\vec{E} \times \vec{B}$
(D) None of these

Ajay Singhal

Ajay Singhal

Numerade Educator

Problem 2

The charge on a parallel plate capacitor is varying as $q=q_{0} \sin 2 \pi \cdot n t$ The plates are very large and close together. Neglecting the edge effects, the displacement current through the capacitor is
(A) $\frac{q}{\varepsilon_{0} A}$
(B) $\frac{q_{0}}{\varepsilon_{0}} \sin 2 \pi n t$
(C) $2 \pi n q_{0} \cos \pi n t$
(D) $\frac{2 \pi n q_{0}}{\varepsilon_{0}} \cos 2 \pi n t$

Narayan Hari

Numerade Educator

Problem 3

The value of magnetic field between plates of capacitor, at distance of $1 \mathrm{~m}$ from centre where electric field varies by $10^{10} \mathrm{~V} / \mathrm{m} / \mathrm{s}$ will be
(A) $5.56 \mathrm{~T}$
(B) $5.56 \mu \mathrm{T}$
(C) $5.56 \mathrm{mT}$
(D) $55.6 \mathrm{nT}$

Narayan Hari

Numerade Educator

Problem 4

The electromagnetic waves do not transport
(A) Energy
(B) Charge
(C) Momentum
(D) Information

Ajay Singhal

Numerade Educator

Problem 5

A capacitor is connected in an electric circuit. Wher key is pressed, the current in the circuit is
(A) Zero
(B) Maximum
(C) Any transient value
(D) Depends on capacitor used

Narayan Hari

Numerade Educator

Problem 6

Displacement current is continuous
(A) when electric field is changing in the circuit.
(B) when magnetic field is changing in the circuit.
(C) in both types of fields.
(D) through wires and resistance only.

Narayan Hari

Numerade Educator

Problem 7

Instantaneous displacement current $1 \mathrm{~A}$ in the space between the parallel plates of $1 \mu \mathrm{F}$ capacitor can be established by changing the potential difference at the rate of
(A) $0.1 \mathrm{~V} / \mathrm{s}$
(B) $1 \mathrm{~V} / \mathrm{s}$
(C) $10^{6} \mathrm{~V} / \mathrm{s}$
(D) $10^{-6} \mathrm{~V} / \mathrm{s}$

Narayan Hari

Numerade Educator

Problem 8

The magnetic field between the plates of a capacitor when $r>R$ is given by
(A) $\frac{\mu_{0} I_{D} r}{2 \pi R^{2}}$
(B) $\frac{\mu_{0} I_{D}}{2 \pi R}$
(C) $\frac{\mu_{0} I_{D}}{2 \pi r}$
(D) $\mathrm{kWU}$

Narayan Hari

Numerade Educator

Problem 9

The magnetic field between the plates of a capacitor is given by $B=\frac{\mu_{0} I r}{2 \pi R^{2}}$
(A) $r \geq R$
(B) $r \leq R$
(C) $r<R$
(D) $r=R$

Narayan Hari

Numerade Educator

Problem 10

The conduction current is the same as displacement current when the source is
(A) AC only
(B) DConly
(C) Both AC and DC
(D) Neither for $\mathrm{AC}$ nor for $\mathrm{DC}$

Narayan Hari

Numerade Educator

Problem 11

The wave function (in S.I. units) for an electromagnetic wave is given as
$$
\Psi(x, t)=10^{3} \sin \pi\left(3 \times 10^{6} x-9-10^{14} t\right)
$$
The speed of the wave as
(A) $9 \times 10^{14} \mathrm{~m} / \mathrm{s}$
(B) $3 \times 10^{8} \mathrm{~m} / \mathrm{s}$
(C) $3 \times 10^{16} \mathrm{~m} / \mathrm{s}$
(D) $3 \times 10^{7} \mathrm{~m} / \mathrm{s}$

Narayan Hari

Numerade Educator

Problem 12

In the above problem, wavelength of the wave is
(A) $666 \mathrm{~nm}$
(B) $666 \AA$
(C) $666 \mu \mathrm{m}$
(D) $6.66 \mathrm{~nm}$

Narayan Hari

Numerade Educator

Problem 13

The Maxwell's four equations are written as
(i) $\oint \vec{E} \cdot \overrightarrow{d s}=\frac{q_{0}}{\varepsilon_{0}}$
(ii) $\oint \vec{B} \cdot \overrightarrow{d s}=0$
(iii) $\oint \vec{E} \cdot \overrightarrow{d l}=\frac{d}{d t} \oint \vec{B} \cdot \overrightarrow{d s}$
(iv) $\oint \vec{B} \cdot \overrightarrow{d s}=\mu_{0} \varepsilon_{0} \frac{d}{d t} \oint \vec{E} \cdot \overrightarrow{d s}$
The equations which have sources of $\vec{E}$ and $\vec{B}$
(A) (i), (ii) and (iii)
(B) (i) and (ii)
(C) (i) and (iii)
(D) (i) and (iv)

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 14

Out of the above four equations which do not contain source field are
(A) (i) and (ii)
(B) (ii) Only
(C) All of four
(D) (iii) Only

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 15

Out of four Maxwell's equations above, which one shows non-existence of monopoles?
(A) (i) and (iv)
(B) (ii) Only
(C) (iii) Only
(D) (i) Only

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 16

Which of the above Maxwell's equations shows that electric field lines do not form closed loops?
(A) (i) only
(B) (ii) only
(C) (iii) only
(D) (iv) only

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 17

In an electromagnetic wave the average energy density is associated with
(A) electric field only.
(B) magnetic field only.
(C) equally with electric and magnetic fields.
(D) average energy density is zero.

Ajay Singhal

Numerade Educator

Problem 18

In an electromagnetic wave the average energy density associated with magnetic field will be
(A) $\frac{1}{2} L I^{2}$
(B) $\frac{B^{2}}{2 \mu_{0}}$
(C) $\frac{1}{2} \mu_{0} B^{2}$
(D) $\frac{1}{2} \frac{q}{B^{2}}$

Narayan Hari

Numerade Educator

Problem 19

In the above problem, the energy density associated with the electric field will be
(A) $\frac{1}{2} C V^{2}$
(B) $\frac{1}{2} \frac{q^{2}}{C}$
(C) $\frac{1}{2} \frac{\varepsilon^{2}}{E}$
(D) $\frac{1}{2} \varepsilon_{0} E^{2}$

Narayan Hari

Numerade Educator

Problem 20

If there were no atmosphere, the average temperature on earth surface would be
(A) Lower
(B) Higher
(C) Same
(D) $0^{\circ} \mathrm{C}$

Narayan Hari

Numerade Educator

Problem 21

In which part of earth's atmosphere is the ozone layer present?
(A) Troposphere
(B) Stratosphere
(C) Ionosphere
(D) Mesosphere

Narayan Hari

Numerade Educator

Problem 22

Kenneley's Heaviside layer lies between
(A) $50 \mathrm{~km}$ to $80 \mathrm{~km}$
(B) $80 \mathrm{~km}$ to $400 \mathrm{~km}$
(C) beyond $110 \mathrm{~km}$
(D) beyond $250 \mathrm{~km}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 23

The ozone layer in earth's atmosphere is crucial for human survival because it
(A) has ions.
(B) reflects radio signals.
(C) reflects ultraviolet ray.
(D) reflects infra red rays.

Narayan Hari

Numerade Educator

Problem 24

The frequency from $3 \times 10^{9} \mathrm{~Hz}$ to $3 \times 10^{10} \mathrm{~Hz}$
(A) High frequency band
(B) Super high frequency band
(C) Ultra high frequency band
(D) High frequency band

Narayan Hari

Numerade Educator

Problem 25

The frequency from 3 to $\mathrm{MHz}$ is known as
(A) Audio band
(B) Medium frequency band
(C) Very high frequency band
(D) High frequency band

Narayan Hari

Numerade Educator

Problem 26

The AM range of radio waves have frequency
(A) Less than $30 \mathrm{MHz}$
(B) More than $30 \mathrm{MHz}$
(C) Less than $20000 \mathrm{~Hz}$
(D) More than $20000 \mathrm{~Hz}$

Narayan Hari

Numerade Educator

Problem 27

The displacement current flows in the dielectric of a capacitor
(A) becomes zero.
(B) has assumed a constant value.
(C) is increasing with time.
(D) is decreasing with time.

Narayan Hari

Numerade Educator

Problem 28

Select wrong statement from the following Electromagnetic waves
(A) are transverse.
(B) travel with same speed in all media.
(C) travel with the speed of light.
(D) are produced by acceleration charge.

Narayan Hari

Numerade Educator

Problem 29

The waves related to telecommunication are
(A) Infra red
(B) Visible light
(C) Microwaves
(D) Ultraviolet rays

Narayan Hari

Numerade Educator

Problem 30

Electromagnetic waves do not transport
(A) Energy
(B) Charge
(C) Momentum
(D) Information

Ajay Singhal

Numerade Educator

Problem 31

The nature of electromagnetic wave is
(A) Longitudinal
(B) Longitudinal stationary
(C) Transverse
(D) Transverse stationary

Narayan Hari

Numerade Educator

Problem 32

Greenhouse effect keeps the earth surface
(A) Cold at night
(B) Dusty and cold
(C) Warm at night
(D) Moist

Narayan Hari

Numerade Educator

Problem 33

A parallel plate capacitor consists of two circular plates each of radius $12 \mathrm{~cm}$ and separated by $5.0 \mathrm{~mm}$. The capacitor is being charged by an external source. The charging is being charged and is equal to $0.15 \mathrm{~A}$. The rate of change of potential difference between the plates will be
(A) $8.173 \times 10^{7} \mathrm{~V} / \mathrm{s}$
(B) $7.817 \times 10^{8} \mathrm{~V} / \mathrm{s}$
(C) $1.873 \times 10^{9} \mathrm{~V} / \mathrm{s}$
(D) $3.781 \times 10^{10} \mathrm{~V} / \mathrm{s}$

Narayan Hari

Numerade Educator

Problem 34

In the above problem, the displacement current is
(A) $15 \mathrm{~A}$
(B) $1.5 \mathrm{~A}$
(C) $0.15 \mathrm{~A}$
(D) $0.015 \mathrm{~A}$

Narayan Hari

Numerade Educator

Problem 35

The wave emitted by any atom or molecule must have some finite total length which is known as the coherence length. For sodium light, this length is $2.4 \mathrm{~cm}$. The number of oscillations in this length will be
(A) $4.068 \times 10^{5}$
(B) $4.068 \times 10^{6}$
(C) $4.068 \times 10^{7}$
(D) $4.068 \times 10^{8}$

Narayan Hari

Numerade Educator

Problem 36

In the above problem, the coherence time will be
(A) $8 \times 10^{-8} \mathrm{~s}$
(B) $8 \times 10^{-9} \mathrm{~s}$
(C) $8 \times 10^{-10} \mathrm{~s}$
(D) $8 \times 10^{-11} \mathrm{~s}$

Narayan Hari

Numerade Educator

Problem 37

A parallel plate capacitor made to circular plates each of radius $R=6 \mathrm{~cm}$ has capacitance $C=100 \mathrm{pF}$. The capacitance is connected to a $230 \mathrm{~V}$ AC supply with an angular frequency of $300 \mathrm{rad} / \mathrm{s}$. The rms value of conduction current will be
(A) $5.7 \mu \mathrm{A}$
(B) $6.3 \mu \mathrm{A}$
(C) $9.6 \mu \mathrm{A}$
(D) $6.9 \mu \mathrm{A}$

Narayan Hari

Numerade Educator

Problem 38

In the above problem, the displacement current will be
(A) $6.9 \mu \mathrm{A}$
(B) $9.6 \mu \mathrm{A}$
(C) $6.3 \mu \mathrm{A}$
(D) $5.7 \mu \mathrm{A}$

Narayan Hari

Numerade Educator

Problem 39

In Q. 37, the value of $B$ at a point $3 \mathrm{~cm}$ from the axis between the plates will be
(A) $1.63 \times 10^{-8} \mathrm{~T}$
(B) $1.63 \times 10^{-9} \mathrm{~T}$
(C) $1.63 \times 10^{-10} \mathrm{~T}$
(D) $1.63 \times 10^{-11} \mathrm{~T}$

Narayan Hari

Numerade Educator

Problem 40

A plane electromagnetic wave of frequency $40 \mathrm{MHz}$ travels in free space in the $x$-direction. At some point and at some instant, the electric field $\vec{E}$ has its maximum value of $750 \mathrm{~N} / \mathrm{C}$ in $y$-direction. The wavelength of the wave is
(A) $3.5 \mathrm{~m}$
(B) $5.5 \mathrm{~m}$
(C) $7.5 \mathrm{~m}$
(D) $9.5 \mathrm{~m}$

Narayan Hari

Numerade Educator

Problem 41

In the above problem, the period of the wave will be
(A) $2.5 \mu \mathrm{s}$
(B) $0.25 \mu \mathrm{s}$
(C) $0.025 \mu \mathrm{s}$
(D) None of these

Narayan Hari

Numerade Educator

Problem 42

In Q. 40 , the magnitude and direction of magnetic field will be
(A) $2.5 \mu \mathrm{T}$ in $x$-direction
(B) $2.5 \mu \mathrm{T}$ in $y$-direction
(C) $2.5 \mu \mathrm{T} z$-direction
(D) None of these

Narayan Hari

Numerade Educator

Problem 43

In Q. 40 , the angular frequency of e.m.f. wave will be (in $\mathrm{rad} / \mathrm{s})$
(A) $8 \pi \times 10^{7}$
(B) $4 \pi \times 10^{6}$
(C) $4 \pi \times 10^{5}$
(D) $8 \pi \times 10^{4}$

Narayan Hari

Numerade Educator

Problem 44

In Q. 40 , the propagation constant of the wave will be
(A) $8.38 \mathrm{~m}^{-1}$
(B) $0.838 \mathrm{~m}^{-1}$
(C) $4.19 \mathrm{~m}^{-1}$
(D) $0.419 \mathrm{~m}^{-1}$

Narayan Hari

Numerade Educator

Problem 45

The sun delivers $10^{3} \mathrm{~W} / \mathrm{m}^{2}$ of electromagnetic flux to the earth's surface. The total power that is incident on a roof of dimensions $8 \mathrm{~m} \times 20 \mathrm{~m}$, will be
(A) $6.4 \times 10^{3} \mathrm{~W}$
(B) $3.4 \times 10^{4} \mathrm{~W}$
(C) $1.6 \times 10^{5} \mathrm{~W}$
(D) None of these

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 46

In the above problem, the radiation force on the
(A) $3.33 \times 10^{-5} \mathrm{~N}$
(B) $5.33 \times 10^{-4} \mathrm{~N}$
(C) $7.33 \times 10^{-3} \mathrm{~N}$
(D) None of these

Narayan Hari

Numerade Educator

Problem 47

In Q. 45 , the solar energy incident on the roof in 1 hour will be
(A) $5.76 \times 10^{8} \mathrm{~J}$
(B) $5.76 \times 10^{7} \mathrm{~J}$
(C) $5.76 \times 10^{6} \mathrm{~J}$
(D) $5.76 \times 10^{5} \mathrm{~J}$

Narayan Hari

Numerade Educator

Problem 48

The sun radiates electromagnetic energy at the rate of $3.9 \times 10^{26} \mathrm{~W}$. Its radius is $6.96 \times 10^{8} \mathrm{~m}$. The intensity of sun light at the solar surface will be
(A) $1.4 \times 10^{4}$
(B) $2.8 \times 10^{5}$
(C) $4.2 \times 10^{6}$
(D) $5.6 \times 10^{7}$

Narayan Hari

Numerade Educator

Problem 49

In the above problem, if the distance from the sun to the earth is $1.5 \times 10^{11} \mathrm{~m}$, then the intensity of sunlight on earth's surface will be (in $\mathrm{W} / \mathrm{m}^{2}$ )
(A) $1.38 \times 10^{3}$
(B) $2.76 \times 10^{4}$
(C) $5.52 \times 10^{5}$
(D) $3.74 \times 10^{3}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 50

A laser beam can be focussed on an area equal to the square of its wavelength. A He-Ne laser radiates energy at the rate of $1 \mathrm{nW}$ and its wavelength is $632.8 \mathrm{~nm}$. The intensity of focussed beam will be
(A) $1.5 \times 10^{13} \mathrm{~W} / \mathrm{m}^{2}$
(B) $2.5 \times 10^{9} \mathrm{~W} / \mathrm{m}^{2}$
(C) $3.5 \times 10^{17} \mathrm{~W} / \mathrm{m}^{2}$
(D) None of these

Narayan Hari

Numerade Educator

Problem 51

A flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal plane wave
$$
E_{x}=36 \sin \left(1.20 \times 10^{7} z-3.6 \times 10^{15} t\right) \mathrm{V} / \mathrm{m}
$$
The average intensity of the beam will be
(A) $0.86 \mathrm{~W} / \mathrm{m}^{2}$
(B) $1.72 \mathrm{~W} / \mathrm{m}^{2}$
(C) $3.44 \mathrm{~W} / \mathrm{m}^{2}$
(D) $6.88 \mathrm{~W} / \mathrm{m}^{2}$

Narayan Hari

Numerade Educator

Problem 52

An electric field of $300 \mathrm{~V} / \mathrm{m}$ is confined to a circular area $10 \mathrm{~cm}$ in diameter. If the field is increasing at the rate of $20 \mathrm{~V} / \mathrm{m}-\mathrm{s}$, the magnitude of magnetic field at a point $15 \mathrm{~cm}$ from the centre of the circle will be
(A) $1.85 \times 10^{-15} \mathrm{~T}$
(B) $1.85 \times 10^{-16} \mathrm{~T}$
(C) $1.85 \times 10^{-17} \mathrm{~T}$
(D) $1.85 \times 10^{-18} \mathrm{~T}$

Narayan Hari

Numerade Educator

Problem 53

A lamp emits monochromatic green light uniformly in all directions. The lamp is $3 \%$ efficient in converting electrical power to electromagnetic waves and consumes $100 \mathrm{~W}$ of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of $10 \mathrm{~m}$ from the lamp will be
(A) $1.34 \mathrm{~V} / \mathrm{m}$
(B) $2.68 \mathrm{~V} / \mathrm{m}$
(C) $5.36 \mathrm{~V} / \mathrm{m}$
(D) $9.37 \mathrm{~V} / \mathrm{m}$

Narayan Hari

Numerade Educator

Problem 54

A plane electromagnetic wave of wave intensity $6 \mathrm{~W} / \mathrm{m}^{2}$ strikes a small mirror of area $40 \mathrm{~cm}^{2}$, held perpendicular to the approaching wave. The momentum transferred by the wave to the mirror each second will be
(A) $6.4 \times 10^{-7} \mathrm{~kg}-\mathrm{m} / \mathrm{s}$
(B) $4.8 \times 10^{-8} \mathrm{~kg}-\mathrm{m} / \mathrm{s}$
(C) $3.2 \times 10^{-9} \mathrm{~kg}-\mathrm{m} / \mathrm{s}$
(D) $1.6 \times 10^{-10} \mathrm{~kg}-\mathrm{m} / \mathrm{s}$

Narayan Hari

Numerade Educator

Problem 55

In the above problem, the radiation force on the mirror will be
(A) $6.4 \times 10^{-7} \mathrm{~N}$
(B) $4.8 \times 10^{-8} \mathrm{~N}$
(C) $3.2 \times 10^{-9} \mathrm{~N}$
(D) $1.6 \times 10^{-10} \mathrm{~N}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 56

In the above problem, the wavelength of the wave will be
(A) $1.5 \mathrm{~m}$
(B) $66.6 \mathrm{~m}$
(C) $1.5 \mathrm{~cm}$
(D) $66.6 \mathrm{~cm}$

Narayan Hari

Numerade Educator

Problem 57

In Q. 5, the energy density at a distance $3.5 \mathrm{~m}$ from the source will be (in joule/m $^{3}$ )
(A) $1.73 \times 10^{-5}$
(B) $1.73 \times 10^{-6}$
(C) $1.73 \times 10^{-7}$
(D) $1.73 \times 10^{-8}$

Narayan Hari

Numerade Educator

Problem 58

A $100 \mathrm{pF}$ capacitor is connected to a $230 \mathrm{~V}, 50 \mathrm{~Hz} \mathrm{AC}$ source. The rms value of conduction current will be
(A) $7.2 \times 10^{-6} \mathrm{~A}$
(B) $3.6 \times 10^{-5} \mathrm{~A}$
(C) $1.8 \times 10^{-4} \mathrm{~A}$
(D) $0.9 \times 10^{-3} \mathrm{~A}$

Narayan Hari

Numerade Educator

Problem 59

What should be the height of transmitting antenna if the TV telecast is to cover a radius of $128 \mathrm{~km} ?$
(A) $1560 \mathrm{~m}$
(B) $1280 \mathrm{~m}$
(C) $1050 \mathrm{~m}$
(D) $79 \mathrm{~m}$

Narayan Hari

Numerade Educator

Problem 60

The area to be covered for TV telecast is doubled, then the height of transmitting antenna (TV tower) will have to be
(A) Doubled
(B) Halved
(C) Quardupled
(D) Kept unchanged

Narayan Hari

Numerade Educator

Problem 61

Infrared radiation is detected by
(A) Spectrometer
(B) Pyrometer
(C) Nanometer
(D) Photometer

Narayan Hari

Numerade Educator

Problem 62

Electromagnetic waves are transverse in nature is evident by $[\mathbf{2 0 0 2}]$
(A) Polarization
(B) Interference
(C) Reflection
(D) Diffraction

Narayan Hari

Numerade Educator

Problem 63

Which of the following are not electromagnetic waves? [2002]
(A) Cosmic rays
(B) Gamma rays
(C) $\beta$-rays
(D) $x$-rays

Narayan Hari

Numerade Educator

Problem 64

Consider telecommunication through optical fibres. Which of the following statements is not true? [2003]
(A) Optical fibres can be of graded refractive index.
(B) Optical fibres are subject to electromagnetic interference from outside.
(C) Optical fibres have extremely low transmission loss.
(D) Optical fibres may have homogeneous core with a suitable cladding.

Narayan Hari

Numerade Educator

Problem 65

An electromagnetic wave of frequency $v=3.0 \mathrm{MHz}$ passes from vacuum into a dielectric medium with permittivity $\varepsilon=4.0 .$ Then
(A) wavelength is doubled and the frequency remains unchanged.
(B) wavelength is doubled and frequency becomes half.
(C) wavelength is halved and frequency remains unchanged.
(D) wavelength and frequency both remain unchanged.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 66

The rms value of the electric field of the light coming from the sun is $720 \mathrm{~N} / \mathrm{C}$. The average total energy density of the electromagnetic wave is [2006]
(A) $3.3 \times 10^{-3} \mathrm{~J} / \mathrm{m}^{3}$
(B) $4.58 \times 10^{-6} \mathrm{~J} / \mathrm{m}^{3}$
(C) $6.37 \times 10^{-9} \mathrm{~J} / \mathrm{m}^{3}$
(D) $81.35 \times 10^{-12} \mathrm{~J} / \mathrm{m}^{3}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 67

This question has Statement 1 and Statement 2. Of the four choices given after the statements, choose the one that best describes the two statements. Statement-1: Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals are in general, less stable than ground wave signals. Statement-2: The state of ionosphere varies from hour to hour, day to day and season to season.
(A) Statement- 1 is true, Statement-2 is false.
(B) Statement-1 is true, Statement-2 is true, Statement-2 is the correct explanation of Statement-1.
(C) Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of Statement 1 .
(D) Statement 1 is false, Statement 2 is true.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 68

An electromagnetic wave in vacuum has the electric and magnetic fields $\vec{E}$ and $\vec{B}$, which are always perpendicular to each other. The direction of polarizations is given by $\vec{X}$ and that of wave propagation by $\vec{k}$ Then $[2012]$
(A) $\vec{X} \| \vec{E}$ and $\vec{k} \| \vec{E} \times \vec{B}$
(B) $\vec{X} \| \vec{B}$ and $\vec{K} \| \vec{E} \times \vec{B}$
(C) $\vec{X} \| \vec{E}$ and $\vec{k} \| \vec{B} \times \vec{E}$
(D) $\vec{X} \| \vec{B}$ and $\vec{k} \| \vec{B} \times \vec{E}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 69

A radar has power of $1 \mathrm{~kW}$ and is operating at a frequency of $10 \mathrm{GHz}$. It is located on a mountain top of height $500 \mathrm{~m}$. The maximum distance up to which it can detect object located on the surface of the earth (Radius of earth $=6.4 \times 10^{6} \mathrm{~m}$ ) is
(A) $16 \mathrm{~km}$
(B) $40 \mathrm{~km}$
(C) $64 \mathrm{~km}$
(D) $80 \mathrm{~km}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 70

The magnetic field in a travelling electromagnetic wave has a peak value of $20 \mathrm{nT}$. The peak value of electric field strength is
(A) $12 \mathrm{~V} / \mathrm{m}$
(B) $3 \mathrm{~V} / \mathrm{m}$
(C) $6 \mathrm{~V} / \mathrm{m}$
(D) $9 \mathrm{~V} / \mathrm{m}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 71

During the propagation of electromagnetic waves in a medium
(A) Both electric and magnetic energy densities are zero.
(B) Electric energy density is half of the magnetic energy density.
(C) Electric energy density is half of the magnetic energy density.
(D) Flectric energy density is equal to the magnetic energy density.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 72

Match List-I (Electromagnetic wave type) with List-II (Its association/application)and select the correct option from the choices given below the lists. [2014]

$$
\begin{array}{ll}
\text { List-I } & \text { List-II } \\
\hline \text { (P) Infrared wave } & \text { (i) To treat muscular strain } \\
\text { (Q) Radio waves } & \text { (ii) For broadcasting } \\
\text { (R) X-rays } & \text { (iii) To detect fracture of bones } \\
\text { (S) Ultraviolet } & \text { (iv) Absorbed by the ozone } \\
\text { rays } & \text { layer of the atmosphere }
\end{array}
$$
$$
\begin{array}{c|c|c|c|c}
& \text { P } & \text { Q } & \text { R } & \text { S } \\
\hline \text { A } & \text { (i) } & \text { (ii) } & \text { (iii) } & \text { (iv) } \\
\hline \text { B } & \text { (iv) } & \text { (iii) } & \text { (ii) } & \text { (i) } \\
\hline \text { C } & \text { (i) } & \text { (ii) } & \text { (iv) } & \text { (iii) } \\
\hline \text { D } & \text { (iii) } & \text { (ii) } & \text { (i) } & \text { (iv) } \\
\hline
\end{array}
$$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 73

A red LED emits light at $0.1$ watt uniformly around it. The amplitude of the electric field of the light at a distance of $1 \mathrm{~m}$ from the diode is [2015]
(A) $2.45 \mathrm{~V} / \mathrm{m}$
(B) $5.48 \mathrm{~V} / \mathrm{m}$
(C) $7.75 \mathrm{~V} / \mathrm{m}$
(D) $1.73 \mathrm{~V} / \mathrm{m}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 74

Arrange the following electromagnetic radiations per quantum in the order of increasing energy:
[2016]
(i) Blue light
(ii) Yellow light
(iii) X-ray
(iv) Radio wave
(A) (i), (ii), (iv) and (iii)
(B) (iii), (i), (ii) and (iv)
(C) (ii), (i), (iv) and (iii)
(D) (iv), (ii), (i) and (iii)

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator