Electromagnetic Waves MCQ Questions & Answers in Electrostatics and Magnetism | Physics
Learn Electromagnetic Waves MCQ questions & answers in Electrostatics and Magnetism are available for students perparing for IIT-JEE, NEET, Engineering and Medical Enternace exam.
41.
The electric and the magnetic field, associated with an electromagnetic wave, propagating along the $$+z$$ -axis, can be represented by
A
$$\left[ {E = {E_0}\hat k,B = {B_0}\hat i} \right]$$
B
$$\left[ {E = {E_0}\hat j,E = {B_0}\hat j} \right]$$
C
$$\left[ {E = {E_0}\hat j,B = {B_0}\hat k} \right]$$
D
$$\left[ {E = {E_0}\hat i,B = {B_0}\hat j} \right]$$
As we know that $$\mu = E \times B = {E_0}\hat i + {B_0}\hat j$$
$$E \times B$$ points in the direction of wave propagation.
42.
Which of the following shows green house effect?
A
Ultraviolet rays
B
Infrared rays
C
X-rays
D
None of these
Answer :
Infrared rays
Infrared radiations reflected by low lying clouds and keeps the earth warm.
43.
A new system of unit is evolved in which the values of $${\mu _0}$$ and $${ \in _0}$$ are 2 and 8 respectively. Then the speed of light in this system will be
44.
The structure of solids is investigated by using
A
cosmic rays
B
X-rays
C
$$\gamma $$-rays
D
infrared radiations
Answer :
X-rays
Due to high penetrating power of X-rays, X-rays are used for investigation of structure of solids. Lane spot method and rotating cylinder method are used for this purpose. X-rays fall on solid under investigation and their structure is received on photographic plate.
45.
If $${\varepsilon _0}$$ and $${\mu _0}$$ are respectively the electric permittivity and magnetic permeability of free space, $$\varepsilon $$ and $$\mu $$ are the corresponding quantities in a medium, the index of refraction of the medium is
A
$$\sqrt {\frac{{{\varepsilon _0}{\mu _0}}}{{\varepsilon \mu }}} $$
B
$$\sqrt {\frac{{\varepsilon \mu }}{{{\varepsilon _0}{\mu _0}}}} $$
C
$$\sqrt {\frac{{{\varepsilon _0}\mu }}{{\varepsilon {\mu _0}}}} $$
D
$$\sqrt {\frac{\varepsilon }{{{\varepsilon _0}}}} $$
Refractive index of medium is given by
$$\eqalign{
& n = \sqrt {{\mu _r}{\varepsilon _r}} . \cr
& {\text{Here,}}\,\,\mu = {\mu _0}{\mu _r} \Rightarrow {\mu _r} = \frac{\mu }{{{\mu _0}}} \cr
& {\text{and }}\varepsilon = {\varepsilon _0}{\varepsilon _r} \Rightarrow {\varepsilon _r} = \frac{\varepsilon }{{{\varepsilon _0}}} \cr
& \therefore n = \sqrt {\frac{\mu }{{{\mu _0}}} \cdot \frac{\varepsilon }{{{\varepsilon _0}}}} = \sqrt {\frac{{\varepsilon \mu }}{{{\varepsilon _0}{\mu _0}}}} \cr} $$
46.
Which of the following electromagnetic waves has minimum frequency ?
A
Microwaves
B
Audible waves
C
Ultrasonic wave
D
Radio waves
Answer :
Audible waves
Audible waves are not electromagnetic wave.
47.
The frequency of electromagnetic wave, which is best suited to observe a particle of radius $$3 \times {10^{ - 4}}cm,$$ is of the order of
A
$${10^{15}}$$
B
$${10^{14}}$$
C
$${10^{13}}$$
D
$${10^{12}}$$
Answer :
$${10^{14}}$$
Size of particle of any wave is given in terms of wavelength
$$\eqalign{
& \lambda = \frac{c}{\nu } \cr
& {\text{Here,}}\,\,\lambda = 3 \times {10^{ - 4}}cm, \cr
& {\text{Velocity of light in vacuum,}}\,c = 3 \times {10^{10}}cm/s \cr
& \therefore 3 \times {10^{ - 4}} = \frac{{3 \times {{10}^{10}}}}{\nu } \cr
& \therefore {\text{Frequency of electromagnetic wave}}\,\nu = {10^{14}}\,Hz \cr} $$
48.
The magnetic field between the plates of radius $$12\,cm$$ separated by distance of $$4\,mm$$ of a parallel plate capacitor of capacitance $$100\,pF$$ along the axis of plates having conduction current of $$0.15\,A$$ is
A
zero
B
$$1.5\,T$$
C
$$15\,T$$
D
$$0.15\,T$$
Answer :
zero
As $$B \propto r,$$ since the point is on the axis where $$r = 0,$$ So $$B = 0$$
50.
Out of the following options which one can be used to produce a propagating electromagnetic wave?
A
A stationary charge
B
A chargeless particle
C
An accelerating charge
D
A charge moving at constant velocity
Answer :
An accelerating charge
A particle is known that an electric charge at rest has electric field in the region around it, but no magnetic field. A moving charge produces both the electric and magnetic fields. If a charge is moving with a constant velocity, the electric and magnetic fields will not change with time, hence no $$EM$$ wave will be produced. But if the charge is moving with a non-zero acceleration, both the electric and magnetic field will change with space and time, it then produces $$EM$$ wave. This shows that accelerated charge emits electromagnetic waves.