Maharashtra Board Class 11 Physics Solution Chapter 13 – Electromagnetic Waves and Communication System
Balbharati Maharashtra Board Class 11 Physics Solution Chapter 13: Electromagnetic Waves and Communication System. Marathi or English Medium Students of Class 11 get here Electromagnetic Waves and Communication System full Exercise Solution.
|Maharashtra Class 11|
Electromagnetic Waves and Communication System
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
(D) Visible light
When solar light comes on earth most part gets absorbed by earth and heats up the earth called global warming this heat get radiated in the form of infrared radiations.
ii) Earth’s atmosphere is richest in
When solar light comes on earth most part gets absorbed by earth and heats up the earth called global warming this heat get radiated in the form of infrared radiations hence Earth’s atmosphere is richest in infrared radiations(IR).
iii) How does the frequency of a beam of ultraviolet light change when it travels from air into glass?
(A) No change
(D) remains same
Frequency is property of source of light and it is independent on medium hence when medium changes from air to glass frequency remains the same.
iv) The direction of EM wave is given by
(B) E. B
(C) along E
(D) along B
Direction of EM wave is always perpendicular to electric and magnetic field vectors along the direction of their cross product E×B.
v) The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to
We have formula for maximum distance range for transmission
d α h1/2
vi) The waves used by artificial satellites for communication purposes are
(B) AM radio waves
(C) FM radio waves
Microwaves are used by artificial satellites for communication purposes.
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
We have formula for range (d) as
h= d2/2R= (640)2/2*6400
h= 32000 m
2.) Answer briefly.
i) State two characteristics of an EM wave.
Answer- there is many characteristics of EM wave following are two
- The energy of EM waves is distributed equally between the electric and magnetic fields. IE = IB.
- In free space, EM waves travel with velocity c, equal to that of light in free space.
ii) Why are microwaves used in radar?
Answer- microwaves used in radar to find out location of different objects present at different locations.
iii) What are EM waves?
Answer- EM waves are electromagnetic waves consist of electric and magnetic fields perpendicular to each other and vibrating periodically perpendicular to direction of propagation of wave caused by accelerated charged particles.
iv) How are EM waves produced?
Answer- According to Maxwell’s theory any charge in accelerated motion gives rise to EM waves. When accelerated charge travels it produces oscillating electric and magnetic field. Changing electric field produces magnetic field and this magnetic field again give rise to the electric field .in this way EM waves are produced and travelled in space.
v) Can we produce a pure electric or magnetic wave in space? Why?
Answer- NO. We can’t produce either pure electric or magnetic wave in space because in space a electric field will lead to formation of magnetic field and not the other electric field hence produces electromagnetic waves and not just pure electric waves. Hence pure electric waves or pure magnetic waves can’t exist in space.
vi) Does an ordinary electric lamp emit EM waves?
vii) Why do light waves travel in vacuum whereas sound wave cannot?
Answer- light waves are made up of electric and magnetic fields in which electric field produces magnetic field and vice versa and produces transverse waves hence they don’t require material medium to travel on the other hand sound waves are longitudinal waves produced due to vibrations of medium particles as in vacuum there is no material medium presents hence no vibrations hence no sound wave.
viii) What are ultraviolet rays? Give two uses.
Answer- ultraviolet rays are electromagnetic radiations having wavelength shorter than visible light hence invisible to human beings. There are many uses of ultraviolet rays few are mention below.
Used in burglar alarms and security systems.
Ultraviolet rays destroy germs and bacteria and hence they are used for purification of water.
ix) What are radio waves? Give its two uses.
Answer- radio waves are electromagnetic waves having very long wavelengths ranging from a few centimeters to a few hundreds of kilometers. Uses of radio waves are
They are used for transmission of TV signals.
Radio waves are used for wireless communication and in cellular phones for vocal communication.
x) Name the most harmful radiation entering the Earth’s atmosphere from the outer space.
Answer- Ultraviolet radiations from sun.
xi) Give reasons for the following:
(i) Long distance radio broadcast uses short wave bands.
Answer- Long distance radio broadcast uses short wave bands because waves reflected by ionosphere lies in this band only.
(ii) Satellites are used for long distance TV transmission.
Answer- TV signals are high frequency signals and can pass through ionosphere directly so they cannot be transmitted using sky wave or space wave propagation hence Satellites are used for long distance TV transmission.
xii) Name the three basic units of any communication system.
Answer- transmitter, communication channel and receiver.
xiii) What is a carrier wave?
Answer- Low frequency signals cannot be transmitted over large distances. Hence these signals are superimposed on high frequency wave named as carrier wave.
xiv) Why high frequency carrier waves are used for transmission of audio signals?
Answer- Audio signals have low frequency and Low frequency signals lost the data if transmitted for large distances hence these signals are superimposed on high frequency carrier waves.
xv) What is modulation?
Answer- the process of superposition of low frequency signals on high frequency carrier waves so that low frequency signals can be transmitted over large distances is called modulation of signal.
xvi) What is meant by amplitude modulation?
Answer- in modulation some characteristics like amplitude, frequency or phase of carrier wave changes in synchronization with the signal. When the amplitude in particular of carrier wave changes in synchronization with amplitude of signal to be transmitted then modulation is called amplitude modulation.
xvii) What is meant by noise?
Answer- a random unwanted signal is called noise.
xviii) What is meant by bandwidth?
Answer- bandwidth represents range of frequencies within which it operates hassle free and efficiently.
xix) What is demodulation?
Answer- demodulation is reverse of modulation in which original signal is extracted from modulated wave at receivers end.
xx) What type of modulation is required for television broadcast?
Answer- amplitude modulation is required as it has large range s cheaper.
xxi) How does the effective power radiated by an antenna vary with wavelength?
Answer- power radiated by an antenna varies inversely with the square of wavelength of the signal.
xxii) Why should broadcasting programs use different frequencies?
Answer- if broadcasting Programs use same frequency then signals with same frequency will get mixed up and signal will become undistinguishable to avoid this broadcasting programs use different frequencies.
xxiii) Explain the necessity of a carrier wave in communication.
Answer- without carrier wave signal can be transmitted but it requires large antenna for transmission and also requires large amplification of low frequency signals for transmission over desired distances hence it is feasible to use carrier waves in communication.
xxiv) Why does amplitude modulation gives noisy reception?
Answer- in case of amplitude modulation amplitude changes with the amplitude of transmitting signal so if due to any reason like change in impedance in circuit or change in capacitance or inductance in circuit due to heat or any reason it changes magnitude of signal which interns leads to change in amplitude hence noise is created.
xxv) Explain why modulation is needed?
Answer- modulation is process in which transmitting signal is superimposed on carrier wave of high frequency. So different frequencies can be assigned to carrier waves so that travelling signal will have different frequencies and they will not get mixed up and hassle free transmission takes place.