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Electromagnetic Waves

48 Questions Start Allen Test
All Exams Allen
Q26 Allen 2. PYQ MCQ
An em wave is propagating in a medium with a velocity $\vec{V} = V\hat{i}$ . 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 :-
A.
-z direction
B.
+z direction
C.
-y direction
D.
-x direction
Q27 Allen 2. PYQ MCQ
For a transparent medium relative permeability and permittivity, $\mu_{r}$ and $\epsilon_{r}$ are 1.0 and 1.44 respectively. The velocity of light in this medium would be,
A.
$2.5 \times 10^{8}$ m/s
B.
$3 \times 10^{8}$ m/s
C.
$2.08 \times 10^{8}$ m/s
D.
$4.32 \times 10^{8}$ m/s
Q28 Allen 2. PYQ MCQ
Light with an average flux of $20 \, W/cm^{2}$ falls on a non-reflecting surface at normal incidence having surface area $20 \, cm^{2}$ . The energy received by the surface during time span of 1 minute is:
A.
$48 \times 10^{3}$ J
B.
$10 \times 10^{3}$ J
C.
$12 \times 10^{3}$ J
D.
$24 \times 10^{3}$ J
Q29 Allen 2. PYQ MCQ
The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is: (c = speed of electromagnetic waves)
A.
$1 : c^{2}$
B.
c : 1
C.
1 : 1
D.
1 : c
Q30 Allen 2. PYQ MCQ
The E.M. wave with shortest wavelength among the following is
A.
Ultraviolet rays
B.
X-rays
C.
Gamma-rays
D.
Microwaves
Q31 Allen 2. PYQ MCQ
The magnetic field in a plane electromagnetic wave is given by: $B_y = 2 \times 10^{-7} \sin (\pi \times 10^3 x + 3\pi \times 10^{11} t) T$ Calculate the wavelength.
A.
$\pi \times 10^3 m$
B.
$2 \times 10^{-3} m$
C.
$2 \times 10^3 m$
D.
$\pi \times 10^{-3} m$
Q32 Allen 2. PYQ MCQ
A capacitor of capacitance 'C', is connected across an ac source of voltage V, given by $V = V_{0} \sin \omega t$ . The displacement current between the plates of the capacitor, would then be given by:
A.
$I_{d} = V_{0} \omega C \cos \omega t$
B.
$I_{d} = \frac{V_{0}}{\omega C} \cos \omega t$
C.
$I_{d} = \frac{V_{0}}{\omega C} \sin \omega t$
D.
$I_{d} = V_{0} \omega C \sin \omega t$
Q33 Allen 2. PYQ MCQ
For a plane electromagnetic wave propagating in x-direction, which one of the following combinations gives the correct possible directions for electric field (E) and magnetic field (B) respectively?
A.
$\hat{j} + \hat{k}, \hat{j} + \hat{k}$
B.
$-\hat{j} + \hat{k}, -\hat{j} - \hat{k}$
C.
$\hat{j} + \hat{k}, -\hat{j} - \hat{k}$
D.
$-\hat{j} + \hat{k}, -\hat{j} + \hat{k}$
Q34 Allen 2. PYQ MCQ
When light propagates through a material medium of relative permittivity $\varepsilon_{r}$ and relative permeability $\mu_{r}$ , the velocity of light, v is given by: (c = velocity of light in vacuum)
A.
$v = \sqrt{\frac{\mu_{r}}{\varepsilon_{r}}}$
B.
$v = \sqrt{\frac{\varepsilon_{r}}{\mu_{r}}}$
C.
$v = \frac{c}{\sqrt{\varepsilon_{r}\mu_{r}}}$
D.
v = c
Q35 Allen 2. PYQ Match the Columns
Match Column-I(Electromagnetic waves) with Column-II(Wavelength)
Column-IColumn-II
(A)AM radio waves
(B)Microwaves
(C)Infrared radiations
(D)X-rays
(P)$10^{-10}$ m
(Q)$10^{2}$ m
(R)$10^{-2}$ m
(S)$10^{-4}$ m
A.
A - R, B - Q, C - P, D - S
B.
A - R, B - S, C - Q, D - P
C.
A - Q, B - R, C - S, D - P
D.
A - S, B - R, C - Q, D - P
Q36 Allen 2. PYQ MCQ
The magnetic field of a plane electromagnetic wave is given by $\vec{B}=3\times10^{-8}\cos(1.6\times10^{3}x+48\times10^{10}t)\hat{j}$ , then the associated electric field will be:
A.
$3\times10^{-8}\cos(1.6\times10^{3}x+48\times10^{10}t)\hat{i}V/m$
B.
$3\times10^{-8}\sin(1.6\times10^{3}x+48\times10^{10}t)\hat{i}V/m$
C.
$9\sin(1.6\times10^{3}x-48\times10^{10}t)\hat{k}V/m$
D.
$9\cos(1.6\times10^{3}x+48\times10^{10}t)\hat{k}V/m$
Q37 Allen 2. PYQ MCQ
The ratio of the magnitude of the magnetic field and electric field intensity of a plane electromagnetic wave in free space of permeability $\mu_0$ and permittivity $\varepsilon_0$ is (c - velocity of light in free space)
A.
c
B.
$\frac{1}{c}$
C.
$\frac{c}{\sqrt{\mu_0\varepsilon_0}}$
D.
$\frac{\sqrt{\mu_0\varepsilon_0}}{c}$
Q38 Allen 2. PYQ MCQ
In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of $2.0 \times 10^{10}$ Hz and amplitude 48 Vm $^{-1}$ . Then the amplitude of oscillating magnetic field is: (Speed of light in free space = $3 \times 10^{8}$ m s $^{-1}$ )
A.
$1.6 \times 10^{-8}$ T
B.
$1.6 \times 10^{-7}$ T
C.
$1.6 \times 10^{-6}$ T
D.
$1.6 \times 10^{-9}$ T
Q39 Allen 2. PYQ MCQ
$\epsilon_0$ and $\mu_0$ are the electric permittivity and magnetic permeability of free space respectively. If the corresponding quantities of a medium are $2\epsilon_0$ and $1.5\mu_0$ respectively, the refractive index of the medium will nearly be :
A.
$\sqrt{2}$
B.
$\sqrt{3}$
C.
3
D.
2
Q40 Allen 2. PYQ MCQ
To produce an instantaneous displacement current of 2 mA in the space between the parallel plates of a capacitor of capacitance 4 μF, the rate of change of applied variable potential difference ( $\frac{dV}{dt}$ ) must be:
A.
800 V/s
B.
500 V/s
C.
200 V/s
D.
400 V/s
Q41 Allen 2. PYQ MCQ
A parallel plate capacitor is charged by connecting it to a battery through a resistor. If I is the current in the circuit, then in the gap between the plates:
A.
there is no current.
B.
displacement current of magnitude equal to I flows in the same direction as I.
C.
displacement current of magnitude equal to I flows in a direction opposite to that of I.
D.
displacement current of magnitude greater than I flows but can be in any direction.
Q42 Allen 2. PYQ MCQ
The property which is not of an electromagnetic wave travelling in free space is that:
A.
they are transverse in nature.
B.
the energy density in electric field is equal to energy density in magnetic field.
C.
they travel with a speed equal to $\frac{1}{\sqrt{\mu_{0} \in_{0}}}$
D.
they originate from charges moving with uniform speed.
Q43 Allen 2. PYQ MCQ
The electromagnetic radiation which has the smallest wavelength are :
A.
X-rays
B.
Gamma rays
C.
Ultraviolet rays
D.
Microwaves
Q44 Allen 2. PYQ MCQ
If the ratio of relative permeability and relative permittivity of a uniform medium is 1:4. The ratio of the magnitudes of electric field intensity (E) to the magnetic field intensity (H) of an EM wave propagating in that medium is $\left(\text{Given that } \sqrt{\frac{\mu_0}{\varepsilon_0}} = 120\pi\right)$ :
A.
$30\pi:1$
B.
$1:120\pi$
C.
$60\pi:1$
D.
$120\pi:1$
Q45 Allen 3. ANALYTICAL QUESTIONS MCQ
For EM waves
(a) $\gamma $ rays have higher penetrating power than x rays
(b) x rays have higher penetrating power than $\gamma $ rays
(c) Infrared has higher wavelength than x-rays
(d) Range of visible light is 4000 Å to 7000 Å then correct options are
A.
a, b and d
B.
a, c and d
C.
a and c
D.
a, b and d
Q46 Allen 3. ANALYTICAL QUESTIONS MCQ
Electric field associated with EM wave in free space is given by $\vec{E}=30\sin\left(6\times10^{8}t+kz\right)\hat{i}$ then match the following columns.
Column-IColumn-II
(A)Direction of propagation of EM wave
(B)Wave length of EM wave
(C)Direction of magnetic field of EM wave
(D)Propagation constant ‘K’ of EM wave
(P)−y axis
(Q)$2\ \mathrm{m}^{-1}$
(R)$3.14\ \mathrm{m}$
(S)‘−z’ axis
A.
A-P, B-R, C-S, D-R
B.
A-S, B-R, C-P, D-Q
C.
A-P, B-Q, C-S, D-S
D.
A-S, B-R, C-P, D-P
Q47 Allen 3. ANALYTICAL QUESTIONS MCQ
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): MRI is less harmful medical diagnosis technique than CT-scan
Reason (R): X-rays are used in CT-scan, while MRI uses radio waves.
In the light of the above statements,
choose the most appropriate answer from the options given below:
A.
Both (A) and (R) are true and (R) is the correct explanation of (A).
B.
Both (A) and (R) are true and (R) is NOT the correct explanation of (A).
C.
(A) is true but (R) is false.
D.
(A) is false but (R) is true.
Q48 Allen 3. ANALYTICAL QUESTIONS Match the Columns
Match the Column-I (Law) with Column-II (Mathematical formula)
Column-IColumn-II
(A)Faraday law
(B)Ampere Maxwell law
(C)Gauss law for magnetism
(D)Gauss law for electrostatics
(P)$\oint \vec{E}\cdot d\vec{A}=\frac{q}{\varepsilon_0}$
(Q)$\oint \vec{B}\cdot d\vec{A}=0$
(R)$\oint \vec{E}\cdot d\vec{\ell}=-\frac{d\phi_B}{dt}$
(S)$\oint \vec{B}\cdot d\vec{\ell}=\mu_0 i+\varepsilon_0\mu_0\frac{d\phi_E}{dt}$
A.
A → R, B → Q, C → S, D → P
B.
A → P, B → Q, C → S, D → R
C.
A → P, B → S, C → Q, D → R
D.
A → R, B → S, C → Q, D → P