Additional Questions - Chapter 5 Electromagnetic Waves 12th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

AdditionalQuestions Solved
I Choose the Correct Answer from the Following
Question 1.
The speed of electromagnetic waves in vacuum is given by
(a) $\mu_0 \varepsilon_0$
(b) $\sqrt{\mu_0 \varepsilon_0}$
(c) $\frac{1}{\mu_0 \varepsilon_0}$
(d) $\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$
Answer:
(d) $\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$.
Question 2.
In an electromagnetic wave the electric field vector $E$ and magnetic field vector $B$ are
(a) Perpendicular to each other
(b) Parallel to each other
(c) at $45^{\circ}$ to each other
(d) can have any angle between them
Answer:
(a) Perpendicular to each other.

Question 3.
If $E$ and $B$ be the electric and magnetic field vectors of an electromagnetic wave, then the propagation of the wave is along the direction of
(a) $\mathrm{E}$
(b) $\mathrm{B}$
(c) $\mathrm{E} \times \mathrm{B}$
(d) $\mathrm{Bx} \mathrm{E}$
Answer:
(c) ExB.
Question 4.
In which of the following sequences are the electro magnetic radiations in decreasing order of wavelength
(a) Infrared, radio, X-rays, visible
(b) Radio, infrared, visible, X-rays
(c) Radio, visible, infrared, X-rays
(d) X-rays, visible, infrared, radio
Answer:
(b) Radio, infrared, visible, X-rays .
Question 5.
Ozone layer absorbs
(a) Infrared radiation
(b) Microwaves
(c) Radio waves
(d) UV radiation
Answer:
(d) UV radiation.

Question 6.
A RADAR beam consists of
(a) X-rays
(b) IR rays
(c) UV rays
(d) Microwaves
Answer:
(d) Microwaves.
Question 7.
Which of the following radiations has the longest wavelength?
(a) Radio waves
(b) IR radiation
(c) X-ray
(d) Visible light
Answer:
(a) Radio waves.
Question 8.
TV waves have a wavelength range of $1-10$ metre. Their frequency range in $\mathrm{MHz}$ is
(a) $300-3000$
(b) $3-3000$
(c) $30-300$
(d) $3-30$
Answer:
(c) $30-300$.
Question 9.
The electromagnetic radiation most prevalent in the atmosphere is
(a) Visible light
(b) Infrared
(c) UV
(d) Radio waves
Answer:
(b) Infrared.

Question 10.
Consider an electric charge oscillating with frequency of $10 \mathrm{MHz}$. The radiation emitted will have a wavelength eqal to
(a) $20 \mathrm{~m}$
(b) $30 \mathrm{~m}$
(c) $40 \mathrm{~m}$
(d) $10 \mathrm{~m}$
Answer:
(b) $30 \mathrm{~m}$
Hint:
Wave length, $\lambda=\frac{C}{v}=\frac{3 \times 10^8}{10 \times 10^6}$ $=0.3 \times 10^2=30 \mathrm{~m}$
Question 11.
The frequencies of $\mathrm{X}$-rays, v-rays and UV rays are respectively $\mathrm{a}, \mathrm{b}$ and $\mathrm{c}$. Then
(a) a $<$ b, b $<$ c
(b) $ac$
(c) $a>b, b>c$
(d) $a>b, b Answer:
(b) $ac$.
Question 12.
Greenhouse effect is caused by
(a) UV rays
(b) X-rays
(c) Gamma rays
(d) IR rays
Answer:
(d) IRrays.

Question 13.
If a capacitance $\mathrm{C}$ is connected across an inductance $\mathrm{L}$, then the angular frequency is
(a) $\sqrt{L C}$
(b) $\mathrm{LC}$
(c) $\sqrt{\frac{L}{C}}$
(d) $\sqrt{\frac{1}{L C}}$
Answer:
(d) $\sqrt{\frac{1}{L C}}$.
Question 14.
If $\varepsilon_0$ and $\mu_0$ are the electric permitivity and permeability of free space, $\varepsilon$ and $\mu$ are the corresponding quantities in a medium, then the index of refraction of the medium is
(a) $\sqrt{\frac{\varepsilon_0 \mu}{\varepsilon \mu_0}}$
(b) $\sqrt{\frac{\varepsilon}{\varepsilon_0}}$
(c) $\sqrt{\frac{\varepsilon_0 \mu_0}{\varepsilon \mu}}$
(d) $\sqrt{\frac{\varepsilon \mu}{\varepsilon_0 \mu_0}}$
Answer:
(d) $\sqrt{\frac{\varepsilon \mu}{\varepsilon_0 \mu_0}}$

Hint:
Index of refraction
$
\frac{C}{C_m}=\frac{1}{\sqrt{\mu_0 \varepsilon_0}} \times \frac{\sqrt{\mu \varepsilon}}{1}=\sqrt{\frac{\mu \varepsilon}{\mu_0 \varepsilon_0}}
$
Question 15.
Dimensions of $\frac{1}{\mu_0 \varepsilon_0}$ where symbols have their usual meaning, are
(a) $\left[\mathrm{L}^{-2} \mathrm{~T}^2\right]$
(b) $\left[\mathrm{L}^2 \mathrm{~T}^{-2}\right]$
(c) $\left[\mathrm{LT}^{-1}\right]$
(d) $\left[\mathrm{L}^{-1} \mathrm{~T}\right]$
Answer:
(b) $\left[\mathrm{L}^2 \mathrm{~T}^{-2}\right]$
Hint:
$
C=\frac{1}{\sqrt{\mu_0 \varepsilon_0}} \Rightarrow \frac{1}{\mu_0 \varepsilon_0}=C^2=\left[L^2 \mathrm{~T}^{-2}\right]
$
Question 16.
If $\lambda_{\mathrm{v}}, \lambda_{\mathrm{x}}, \lambda_{\mathrm{m}}$, represent the wavelength of visible light, $\mathrm{X}$-rays and microwaves, respectively, then
(a) $\lambda_{\mathrm{m}}>\lambda_{\mathrm{v}}>\lambda_{\mathrm{x}}$
(b) $\lambda_{\mathrm{m}}>\lambda_{\mathrm{x}}>\lambda_{\mathrm{V}}$
(c) $\lambda_{\mathrm{v}}>\lambda_{\mathrm{m}}>\lambda_{\mathrm{x}}$
(d) $\lambda_{\mathrm{v}}>\lambda_{\mathrm{x}}>\lambda_{\mathrm{m}}$
Answer:
(a) $\lambda_{\mathrm{m}}>\lambda_{\mathrm{v}}>\lambda_{\mathrm{x}}$.

Question 17.
The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to
(a) the speed of light in vacuum
(b) reciprocal of the speed of light in vacuum
(c) the ratio of magnetic permeability to electric susceptibility in vacuum
(d) unity
Answer:
(b) reciprocal of the speed of light in vacuum.
Question 18.
Which of the following radiations forms part of the electromagnetic spectrum?
(a) alpha rays
(b) Beta rays
(c) Gamma rays
(d) Cathode rays
Answer:
(c) Gamma rays.
Question 19.
The ozone layer absorbs radiation of wavelegnths
(a) Less than $3 \times 10^{-7} \mathrm{~m}$
(b) More than $3 \times 10^{-7} \mathrm{~m}$
(c) Less than $3 \times 10^{-5} \mathrm{~m}$
(d) More than $3 \times 10^{-5} \mathrm{~m}$
Answer:
(a) Less than $3 \times 10^{-7} \mathrm{~m}$.
Question 20.
It is possible to take pictures of those objects which are not fully visible to the eye using camera films sensitive to
(a) UV rays
(b) IR rays
(c) Microwaves
(d) Radio waves
Answer:
(b) IRrays.

Question 21.
An electromagnetic wave has wavelength $10 \mathrm{~cm}$. It is in the
(a) Visible region
(b) Radio region
(c) UV region
(d) $\mathrm{X}$-ray region
Answer:
(b) Radio region.
Question 22.
Electromagnetic radiation of frequency $3 \times 10^5 \mathrm{MHz}$ lies in the
(a) Radio wave region
(b) Visible region
(c) IR region
(d) Microwave region
Answer:
(d) Microwave region.
Question 23.
Radio waves and visible light in vacuum have
(a) Same wavelength but different velocities
(b) Same velocity but different wavelength
(c) Different velocities and different wavelengths
(d) Same velocity and same wavelength
Answer:
(b) Same velocity but different wavelength.
Question 24.
Which of the following has maximum frequency?
(a) X-rays
(b) IR rays
(c) UV rays
(d) Radio waves
Answer:

(a) X-rays

Question 25 .
Electromagnetic radiation of frequency $1 \mathrm{GHz}$ lies in
(a) UV region
(b) IR region
(c) Visible region
(d) Microwave region
Answer:
(d) Microwave region.
Question 26.
An electromagnetic wave of frequency $\mathrm{v}=3.0 \mathrm{MHz}$ passes from vacuum into a dielectric
medium with permitivity $s=4.0 \varepsilon_0$. Then
(a) Wavelength is doubled and frequency becomes half
(b) Wavelength is doubled and the frequency remains unchanged.
(c) Wavelength and frequency both remain unchanged
(d) Wavelength is halved and frequency remains unchanged.
Answer:
(d) Wavelength is halved and frequency remain unchanged.
Hint:
When a wave goes from one medium to another, its frequency remains unchanged.
According to equation $\mathrm{C}=\frac{1}{\sqrt{\mu \varepsilon}}$, the speed is halved. Therefore, the wavelength is also halved.
Question 27.
Frequency of a wave is $6 \times 10^{15} \mathrm{~Hz}$. The wave is
(a) Radio wave
(b) Microwave
(c) X-ray
(d) UV rays
Answer:
(d) UV rays.

Question 28.
In an electromagnetic wave the phase difference between electric field $\vec{E}$ and magnetic field $\vec{B}$ is
(a) $\frac{\pi}{4}$
(b) $\frac{\pi}{2}$
(c) $\pi$
(d) zero
Answer:
(d) Zero.
Question 29.
The energy in an electromagnetic wave is
(a) Wholly shared only by electric field vector
(b) Wholly shared only by magnetic field vector
(c) Equally divided between electric and magnetic field
(d) Zero
Answer:
(c) Equally divided between electric and magnetic field.
Question 30.
Electromagnetic waves are produced by
(a) Atoms and molecules in an electrical discharge
(b) Electric device
(c) Accelerated charges
(d) Molecules of hot bodies
Answer:
(c) Accelerated charges.
II Fill in The Blanks
Question 1.
Electromagnetic waves are ............
Answer:
Transverse in nature

Question 2.
Accelerated charge is a source of ............
Answer:
Electromagnetic radiation
Question 3 .
In electromagnetic waves, angle between electric and magnetic field vectors is .................
Answer:
$90^{\circ}$
Question 4.
The electromagnetic waves travel in vacuum or free space with a velocity of .....................
Answer:
$
3 \times 10^8 \mathrm{~ms}^{-1}
$
Question 5 .
The existance of electromagnetic waves was confirmed experimentally by .................
Answer:
Hertz.
Question 6.
Radio frequency wave have wavelength ranging from to...............
Answer: 
$10 \mathrm{~m}$ to $10^4 \mathrm{~m}$
Question 7.
The waves that are used in radio and television communication system is ..........................
Answer:
Radio waves
Question 8.
The frequency range of $\mathrm{X}$-rays is from .................
Answer:
$3 \times 10^{18} \mathrm{~Hz}$ to $10^{16} \mathrm{~Hz}$

Question 9.
Higher frequencies upto $54 \mathrm{mHz}$ are used for .................
Answer:
Short wave brands
Question 10.
The wave that is used in radar communication system is .............
Answer:
Microwaves.
Question 11

........................ rays are used to detect forged documents. 
Answer:
UV-rays.
Question 12
............ is used for treatment of cancer.
Answer:
$\gamma$-rays (gamma rays).
Question 13.
Structure of atoms can be studied with ..................
Answer:
X-rays
Question 14.
When the light emitted directly from a source is examined with a spectrometer, the spectrum obtained is ....................... spectrum.
Answer:
Emission
Question 15.
When the light emitted from a source is made to pass through an absorbing material, the spectrum obtained is called ............... spectrum.
Answer:
Absorption.
Question 16.
Electromagnetic disturbance can be propagated through space ................

Answer:
without the help of material medium.
Question 17.
The velocity of electromagnetic wave is given by the relation ..............
Answer:
$
\mathrm{C}=\frac{1}{\sqrt{\mu_0 \varepsilon_0}}
$
III Match the following
Question 1.

Answer:
(i) $\rightarrow$ (c)
(ii) $\rightarrow$ (a)
(iii) $\rightarrow$ (d)
(iv) $\rightarrow$ (b)
Question 2.

Answer:
(i) $\rightarrow$ (b)
(ii) $\rightarrow$ (a)
(iii) $\rightarrow$ (d)
(iv) $\rightarrow$ (c)
Question 3.

Answer:
(i) $\rightarrow$ (b)
(ii) $\rightarrow$ (a)
(iii) $\rightarrow$ (d)
(iv) $\rightarrow$ (c)
Question 4.

Answer:
(i) $\rightarrow$ (c)
(ii) $\rightarrow$ (a)
(iii) $\rightarrow($ b)
(iv) $\rightarrow$ (d)
IV Assertion and Reason Questions
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) If assertion is true but-reason is false.
(d) If the assertion and reason both are false.
(e) If the assertion is false but reason is true.
Question 1.
Assertion: In Hertz experiment, the electric vector of radiation produced by the source gap is parallel to the gap.
Reason: Production of sparks between the detector gap is maximum when it is placed perpendicular to the source gap.
Answer:
(c) If assertion is true but reason is false.
Explanation:
Hertz experimentally observed that the production of spark between the detection gap is maximum when it is placed parallel to source gap. This means that the electric vector of radiation produced by the source gap is parallel to the two gaps.
Question 2.
Assertion: Ultraviolet radiation are of higher frequency waves are dangerous to human being.
Reason: Ultraviolet radiation are absorbed by the atmosphere.
Answer:
(b) If assertion and reason both are true but reason is not the correct explanation of the assertion.
Explanation:
The wavelength of these waves ranges between $6 \times 10^{-10} \mathrm{~m}$ to $4 \times 10^{-7} \mathrm{~m}$ that is smaller wavelength and higher frequency. They are absorbed by atmosphere and convert oxygen into ozone. They cause skin diseases and they are harmful to eye and cause permanent blindness.
Question 3.
Assertion: Only microwaves are used in RADAR.
Reason: Because microwaves have very small wavelength.
Answer:
(a) If assertion and reason both are true and reason is the correct explanation of the assertion.
Explanation:
In a RADAR, a beam signal is needed in particular direction which is possible if wavelength of wave is very small. Since the wavelength of microwaves is a few millimeter, hence they are used in RADAR.
Question 4.
Assertion: Radio waves bend in a magnetic field.
Reason: Radio waves are electromagnetic in nature.
Answer:
(a) If assertion and reason both are true and reason is the correct explanation of the assertion.
Question 5 .
Assertion:
In the visible spectrum of light, red light is more energetic than green light.
Reason:
The wavelength of red light is more than that of green light.
Answer:
(a) If assertion and reason both are true and reason is the correct explanation of the assertion.
Short Answer Questions
Question 1.
Name the scientist who first predicted the existence of electromagnetic waves.
Answer:
James Clerk Maxwell was first predicted the existence of EM waves.

Question 2.
Distinguish between conduction current and displacement current.
Answer:
Conduction Current:
1. It is due to the flow of electrons in a circuit.
2. It exists even if electrons flow at a uniform rate.
Displacement Current:
1. It is due to time-varying electric field.
2. It does not exist under steady conditions.
Question 3.
What oscillates in electromagnetic waves?
Answer;
In EM waves, electric and magnetic fields oscillate in mutually perpendicular directions. These waves are transverse in nature.
Question 4.
Name the basic source of electromagnetic waves.
Answer:
An electric dipole is a basic source of electro magnetic waves.
Question 5.
State Maxwell's equations.
Answer:
The whole study of electricity and magnetism can be described mathematically with the help of four fundamental equations, called Maxwell's equations. These are stated as follows:
1. Gauss law of electrostatics : $\oint \vec{E} \cdot \vec{d} s=0 \frac{q}{\varepsilon 0}$
2. Gauss law of magnetism: $\oint \vec{E} \cdot \vec{d} \mathrm{~s}=0$
3. Faraday's Law of electromagnetic induction: $\oint \vec{E} \cdot \vec{d} 1=-\frac{d \phi_{\mathrm{B}}}{d t}=-\frac{d}{d t}[\oint \vec{B} \cdot \vec{d} s]$

4. Modified ampere's circuital Law: $\oint \vec{E} \cdot \vec{d} 1=\mu_0\left[\mathrm{I}_{\mathrm{C}}+\varepsilon_0 \frac{d \phi_{\mathrm{E}}}{d t}\right]$
Question 6.
What is electromagnetic spectrum.
Answer:
The orderly distribution of electromagnetic radiations of all types according to their wavelength or frequency into distinct groups having widely differing properties is called electromagnetic spectrum.
Question 7.
Define spectrum.
Answer:
The definite pattern of colours obtained on the screen after dispersion is called as spectrum.
Question 8.
Write down the concept of black body spectrum.
Answer:
When an object bums, it emits colours. That is, it emits electromagnetic radiation which depends on temperature. If the object becomes hot then it glows in red colour. If the temperature of the object is further increased then it glows in reddish-orange colour and becomes white when it is hottest. The spectrum usually called as black body spectrum.
Question 9.
How are radio waves produced?
Answer:
Radiowaves are produced due to accelerated motion of electrons in conducting wires or oscillating circuits.
Question 10.
How are $\mathrm{X}$-rays produced?
Answer:
$\mathrm{X}$-rays are produced due to sudden deceleration of fast moving electrons by a metal target.

Question 11.
How are microwaves produced?
Answer:
Microwaves are produced due to oscillating currents in special vacuum tubes like Klystroms.
Question 12.
What is 'Greenhouse effect'?
Answer:
Greenhouse effect is the phenomenon which keeps the earth's surface warm at night. The earth reflects back infra red part of solar radiation. Infra-red rays are reflected back by low lying clouds and lower atmosphere and keep the earth's surface warm at night.
Question 13.
Why are microwaves used in RADAR?
Answer:
Microwaves have wavelength of the order of a few millimetres. Due to their short wavelengths, these are not diffracted (bent) much by objects of normal dimensions. So they can be transmitted as a beam in a particular direction.
Question 14.
Write down the uses of radiowaves?
Answer:
It is used in radio and television communication systems and also in cellular phones to transmit voice communication in the ultra high frequency band.
Question 15.
Write down the uses of radiowaves?
Answer:
It is used in radar system for aircraft navigation, speed of the vehicle, microwave oven for cooking and very long distance wireless communication through satellites.

Question 16.
Write uses of IR rays (or) infra-red radiations.
Answer:
It is used to produce dehydrated fruits; in green houses to keep the plants warm, heat therapy for muscular pain or sprain, TV remote as a signal carrier, to look through haze fog or mist and used in night vision or infrared photography.
Question 17.
Write down the uses of UV rays (or) Ultraviolet radiations.
Answer:
It is used to destroy bacteria, sterilizing the surgical instruments, burglar alarm, detect the invisible writing, finger prints and also in the study of molecular structure.
Question 18.
What are the uses of $\mathrm{X}$-rays?
Answer:
$\mathrm{X}$-rays are used extensively in studying structures of inner atomic electron shells and crystal structures. It is used in detecting'fractures, diseased organs, formation of bones and stones, observing the progress of healing bones. Further, in a finished metal product, it is used to detect faults, cracks, flaws and holes.
Question 19.
What are emission spectrum? Write its types.
Answer:
When the spectrum of self luminous source is taken, we get emission spectrum. Each source has its own characteristic emission spectrum. The emission spectrum can be divided into three types:
1. Continuous emission spectra.
2. Line emission spectrum (or line spectrum).
3. Band emission spectrum (or band spectrum).
Question 20.
What are absorption spectrum? Write its types

Answer:
When light is allowed to pass through a medium or an absorbing substance then the spectrum .obtained is known as absorption spectrum. It is the characteristic of absorbing substance.
Absorption spectrum is classified into three types:
1. Continuous absorption spectrum.
2. Line absorption spectrum.
3. Band absorption spectrum.
Long Answer Questions
Question 1.
Write short notes on (a) Infrared radiation (b) Ultraviolet radiation (c) Gamma radiation). Answer:
(a) Infrared radiation:
It is produced from hot bodies (also known as heat waves) and also when the molecules undergo rotational and vibrational transitions. The wavelength range is $8 \times 10^{-7} \mathrm{~m}$ to $5 \mathrm{x}$ $10^3 \mathrm{~m}$ and frequency range are $4 \times 10^{14} \mathrm{~Hz}$ to $6 \times 10^{10} \mathrm{~Hz}$. It provides electrical energy to satellites by means of solar cells. It is used to produce dehydrated fruits, in green houses to keep the plants warm, heat therapy for muscular pain or sprain, TV remote as a signal carrier, to look through haze fog or mist and used in night vision or infrared photography.
(b) Ultraviolet radiation:
It is produced by Sun, arc and ionized gases. The wavelength range is $6 \times 10^{-10} \mathrm{~m}$ to $4 \mathrm{x}$ $10^{-7} \mathrm{~m}$ and frequency range are $5 \times 10^{17} \mathrm{~Hz}$ to $7 \times 10^{14} \mathrm{~Hz}$. It has less penetrating power. It can be absorbed by atmospheric ozone and harmful to human body. It is used to destroy bacteria, sterilizing the surgical instruments, burglar alarm, detect the invisible writing, finger prints and also in the study of molecular structure.
(c) Gamma rays:
It is produced by transitions of atomic nuclei and decay of certain elementary particles. They produce chemical reactions on photographic plates, fluorescence, ionisation, diffraction. The wavelength range is $1 \times 10^{-14} \mathrm{~m}$ to $1 \times 10^{-10} \mathrm{~m}$ and frequency range are 3 $\times 10^{22} \mathrm{~Hz}$ to $3 \times 10^{18} \mathrm{~Hz}$. Gamma rays have high penetrating power than $\mathrm{X}$-rays and ultraviolet radiations; it has no charge but harmful to human body. Gamma rays provide information about the structure of atomic nuclei. It is used in radio therapy for the treatment of cancer and tumour, in food industry to kill pathogenic microorganism.