Electromagnetic Wave and Communication System 11 Class 13.Chapter Physics Exercise (Science)
Channel: MB Class
Date: 2021-03-20

Electromagnetic Wave and Communication System 11 Class 13.Chapter Physics Exercise (Science)
Exercise:
1. Choose the correct option.
i) The EM wave emitted by the Sun and 
responsible for heating the Earth’s 
atmosphere due to green house effect is 
(A) Infra-red radiation (B) X ray 
 (C) Microwave (D) Visible light
ii) Earth ’s atmosphere is richest in 
(A) UV (B) IR 
 (C) X-ray (D) Microwaves 
iii) How does the frequency of a beam of 
ultraviolet light change when it travels 
from air into glass?
(A) No change (B) increases 
 (C) decreases (D) remains same
iv) The direction of EM wave is given by 
 (A) E ×B   (B) E
 . B
 
(C) along E

 (D) along B

v) The maximum distance upto which TV 
transmission from a TV tower of height h
can be received is proportional to 
 (A) h1/2 (B) h 
 (C) h3/2 (D) h2
vi) The waves used by artificial satellites for 
communication purposes are 
 (A) Microwave 
 (B) AM radio waves 
 (C) FM radio waves 
 (D) X-rays
vii) If a TV telecast is to cover a radius of 
640 km, what should be the height of 
transmitting antenna?
(A) 32000 m (B) 53000 m
 (C) 42000 m (D) 55000 m 
2. Answer briefly.
i) State two characteristics of an EM wave. 
ii) Why are microwaves used in radar? 
iii) What are EM waves?
iv) How are EM waves produced?
v) Can we produce a pure electric or 
magnetic wave in space? Why?
vi) Does an ordinary electric lamp emit EM 
waves?
vii) Why do light waves travel in vacuum 
whereas sound wave cannot?viii) What are ultraviolet rays? Give two uses.
ix) What are radio waves? Give its two 
uses. 
x) Name the most harmful radiation 
entering the Earth's atmosphere from the 
outer space.
xi) Give reasons for the following:
(i) Long distance radio broadcast uses 
short wave bands.
(ii) Satellites are used for long distance 
TV transmission.
xii) Name the three basic units of any 
communication system.
xiii) What is a carrier wave?
xiv) Why high frequency carrier waves are 
used for transmission of audio signals? 
xv) What is modulation?
xvi) What is meant by amplitude modulation?
xvii) What is meant by noise?
xviii) What is meant by bandwidth?
xix) What is demodulation?
xx) What type of modulation is required for 
television broadcast?
xxi) How does the effective power radiated 
by an antenna vary with wavelength?
xxii) Why should broadcasting programs use 
different frequencies?
xxiii) Explain the necessity of a carrier wave 
in communication.
xxiv) Why does amplitude modulation give 
noisy reception?
xxv) Explain why is modulation needed. 
2. Solve the numerical problem.
i) Calculate the frequency in MHz of a radio 
wave of wavelength 250 m. Remember 
that the speed of all EM waves in vacuum 
is 3.0×108 m/s. 
 [Ans: 1.2 MHz]
ii) Calculate the wavelength in nm of an 
X-ray wave of frequency 2.0×1018 Hz.
 [Ans: 0.15 nm] 
iii) The speed of light is 3×108 m/s. Calculate 
the frequency of red light of wavelength of 
6.5×10-7 m.
 [Ans: υ = 4.6×1014 Hz] 
iv) Calculate the wavelength of a microwave 
of frequency 8.0 GHz.
 [Ans: 3.75 cm]
v) In a EM wave the electric field oscillates 
sinusoidally at a frequency of 2×1010 Hz. 
What is the wavelength of the wave?
 [Ans: 1.5×10-2 m]
vi) The amplitude of the magnetic field part 
of a harmonic EM wave in vacuum is 
B0
= 5×10-7 T. What is the amplitude of the 
electric field part of the wave?
 [Ans: 150V/m]
vii) A TV tower has a height of 200 m. 
How much population is covered by TV 
transmission if the average population 
density around the tower is 1000/km2
? 
(Radius of the Earth = 6.4×106 m)
 [Ans: 8×106
]
viii) Height of a TV tower is 600 m at a given 
place. Calculate its coverage range if the 
radius of the Earth is 6400 km. What 
should be the height to get the double 
coverage area?
 [Ans: 87.6 km, 1200 m]
ix) A transmitting antenna at the top of a tower 
has a height 32 m and that of the receiving 
antenna is 50 m. What is the maximum 
distance between them for satisfactory 
communication in line of sight mode ? 
Given radius of Earth is 6.4×106 m. 
 [Ans: 45.537 km]