Electromagnetic Waves — DPP 1

20 NEET questions from Electromagnetic Waves, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

Attempt this test free 20 questions · 30 minutes · +80 marks
1
Electromagnetic waves are produced due to
  1. A A charge at rest
  2. B A moving charge
  3. C An accelerated charge
  4. D None of these
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Correct answer: C

Em waves are produced by accelerated charged particles
2
The speed of electromagnetic wave in a medium (whose dielectric constant is 2.25 and relative permeability is 4) is equal to
  1. A $0.5 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$
  2. B $0.25 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$
  3. C $0.75 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$
  4. D $1 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$
Show answer & explanation

Correct answer: D

Electromagnetic Waves – NEET-13142
3
Figure shows a circular region of radius R in which uniform magnetic field B exists. The magnetic field is increasing at a rate $\frac{d B}{d t}$. The induced electric field at a distance r from the centre for r < R is
Electromagnetic Waves – NEET-13132
  1. A $\frac{d B}{d t} \frac{r}{2}$
  2. B Zero
  3. C $\frac{d B}{d t}$
  4. D $\frac{d B}{d t} \frac{R^{2}}{2 r}$
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Correct answer: A

Electromagnetic Waves – NEET-13132
4
Red light differs from blue light in its
  1. A Speed
  2. B Frequency
  3. C Intensity
  4. D Amplitude
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Correct answer: B

Frequency is different for each light as they have different wavelengths.
5
Hertz experiment is used for
  1. A Production of electromagnetic wave
  2. B Detection of electromagnetic wave
  3. C Both (A) & (B)
  4. D None of these
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Correct answer: C

Hertz was the scientist who produced and detected the em waves.
6
Which of the following has the largest wavelength?
  1. A Radio wave
  2. B X-ray
  3. C Ultraviolet ray
  4. D Infra-red ray
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Correct answer: A

Radio waves: $10^{-2} \mathrm{~m}$ to $10^{4} \mathrm{~m}$.
7
The following can be arranged in decreasing order of wave number
A. AM radio
B. TV and FM radio
C. Microwave
D. Short radio wave
  1. A A > B > D > C
  2. B C > D > B > A
  3. C A > B > C > D
  4. D D > C > B > A
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Correct answer: B

Decreasing order of wave number
Microwave > short radio wave > TV and FM radio > AM radio.
8
The dimensional formula of $\frac { 1 } { 2 } \varepsilon _ { 0 } E ^ { 2 }$ is (E = electric field)
  1. A $\left[ \mathrm { M } \mathrm { L } \mathrm { T } ^ { - 1 } \right]$
  2. B $\left[ \mathrm { M } \mathrm { L } ^ { 2 } \mathrm {~T} ^ { - 2 } \right]$
  3. C $\left[ \mathrm { M } \mathrm { L } ^ { - 1 } \mathrm {~T} ^ { - 2 } \right]$
  4. D $\left[ \mathrm { M } \mathrm { L } ^ { 2 } \mathrm {~T} ^ { - 1 } \right]$
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Correct answer: C

$\begin{aligned} \frac{1}{2} \varepsilon_{0} E^{2} & =\text { Energy density }=\frac{E}{V}=\frac{\left[\mathrm{ML}^{2} \mathrm{~T}^{-2}\right]}{\left[\mathrm{L}^{3}\right]} \\ & =\left[\mathrm{ML}^{-1} \mathrm{~T}\right]\end{aligned}$
9
If an electromagnetic wave propagating through vacuum is described by $E _ { y } = E _ { 0 } \sin ( k x - \omega t )$; $B _ { z } = B _ { 0 } \sin ( k x - \omega t )$, then
  1. A $E _ { 0 } k = B _ { 0 } \omega$
  2. B $E _ { 0 } B _ { 0 } = \omega k$
  3. C $E _ { 0 } \omega = B _ { 0 } k$
  4. D $E _ { 0 } B _ { 0 } = \frac { \omega } { k }$
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Correct answer: A

$\begin{array}{l}\text { Speed of wave }=\frac{E_{0}}{B_{0}}=\frac{\omega}{k} \\ \therefore \quad k E_{0}=\omega B_{0}\end{array}$
10
Velocity of electromagnetic waves in a medium is
  1. A $\left( \varepsilon _ { 0 } \mu _ { 0 } \right) ^ { - 1 / 2 }$
  2. B $\left( \varepsilon _ { 0 } \varepsilon _ { r } \mu _ { 0 } \mu _ { r } \right) ^ { - 1 / 2 }$
  3. C $3 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s }$
  4. D $\left( \frac { \varepsilon _ { 0 } \varepsilon _ { r } } { \mu _ { 0 } \mu _ { r } } \right) ^ { + 1 / 2 }$
Show answer & explanation

Correct answer: B

$\begin{aligned} \text { Speed of light in medium } & =\frac{1}{\sqrt{\mu \varepsilon}}=\frac{1}{\sqrt{\mu_{0} \mu_{r} \varepsilon_{0} \varepsilon_{r}}} \\ & =\left(\mu_{0} \mu_{r} \varepsilon_{0} \varepsilon_{r}\right)^{-\frac{1}{2}}\end{aligned}$
11
A parallel plate capacitor with circular plates of radius $R$ is being charged as shown. At the instant shown, the displacement current in the region between the plates enclosed between $\frac { R } { 2 }$ and R is given by
Electromagnetic Waves – NEET-13131
  1. A $\frac { 3 } { 4 } i$
  2. B $\frac { 1 } { 4 } i$
  3. C 3i
  4. D $\frac { 4 } { 3 } i$
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Correct answer: A

Electromagnetic Waves – NEET-13131
12
Ozone layer blocks the radiation of wavelength
  1. A Less than $4 \times 10 ^ { - 7 } \mathrm {~m}$
  2. B Between $4 \times 10 ^ { - 7 } \mathrm {~m}$ to $8 \times 10 ^ { - 7 } \mathrm {~m}$
  3. C More than $8 \times 10 ^ { - 7 } \mathrm {~m}$
  4. D None of these
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Correct answer: A

Radiation having wavelength less than $4 \times 10^{-7} \mathrm{~m}$ are blocked by ozone layer
13
The magnetic field in a plane electromagnetic wave is given by $= 2 \times 10 ^ { - 7 } \sin \left( 0.5 \times 10 ^ { 3 } x + 1.5 \times \right. \left. 10 ^ { 11 } t \right) \mathrm { T }$. This electromagnetic wave is
  1. A Visible light
  2. B Infrared
  3. C Microwave
  4. D Radiowave
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Correct answer: D

Electromagnetic Waves – NEET-13149
14
Out of the following, choose the ray which does not travel with the velocity of light
  1. A X-ray
  2. B Microwave
  3. C γ-rays
  4. D β-rays
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Correct answer: D

β-rays do not travel with speed of light, as they are not em waves.
15
In a plane electromagnetic wave, which of the following has/have zero average value in one complete cycle?
(a) Magnetic field
(b) Magnetic energy
(c) Electric field
(d) Electric energy
  1. A (a), (c)
  2. B (b), (c)
  3. C (a), (d)
  4. D All of these
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Correct answer: A

Both $\vec{E}$ and $\vec{B}$ are sinusoidal, so over a complete cycle, its value will be zero.
16
Which of the following represents an infra-red wavelength?
  1. A $10 ^ { - 4 } \mathrm {~cm}$
  2. B $10 ^ { - 5 } \mathrm {~cm}$
  3. C $10 ^ { - 6 } \mathrm {~cm}$
  4. D $10 ^ { - 7 } \mathrm {~cm}$
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Correct answer: A

$10^{-6} \mathrm{~m}$ or $10^{-4} \mathrm{~cm} \Rightarrow$ Infrared
17
Electromagnetic wave is deflected by
  1. A Electric field
  2. B Magnetic field
  3. C Both (1) & (2)
  4. D Neither electric field nor magnetic field
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Correct answer: D

Electromagnetic wave consists of unchanged particle called photons which are neither deflected by electric field nor by magnetic field.
18
Which of the following is not transported by electromagnetic waves?
  1. A Energy
  2. B Momentum
  3. C Charge
  4. D Information
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Correct answer: C

Only energy, momentum and information can be transferred with the help of em waves, not any matter.
19
According to modified Ampere's circuital law (i$_{D}$ = displacement current)
  1. A $\oint \vec { B } \cdot \overrightarrow { d l } = \mu _ { 0 } \left( i _ { C } + \varepsilon _ { 0 } \frac { d \varphi _ { E } } { d t } \right)$
  2. B $\oint \vec { B } \cdot \overrightarrow { d l } = \mu _ { 0 } \varepsilon _ { 0 } \frac { d \varphi _ { E } } { d t }$
  3. C $\oint \vec { B } \cdot \overrightarrow { d l } = \mu _ { 0 } i$
  4. D $\oint \vec { B } \cdot \overrightarrow { d l } = \mu _ { 0 } \left( i _ { C } \frac { d \varphi _ { E } } { d t } + i _ { D } \right)$
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Correct answer: A

According to modified Ampere's circuital law.
$\oint \vec{B} \cdot \overrightarrow{d l}=\mu_{0}\left(i_{C}+\varepsilon_{0} \frac{d \varphi_{E}}{d t}\right)$
20
Which of the following can be used in cancer treatment?
  1. A X-rays
  2. B UV-rays
  3. C γ-rays
  4. D Both (A) & (C)
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Correct answer: D

Both X-rays and γ-rays are used for the treatment of cancer.

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