# Physics class 12 chapter 15 Objective Questions

## Communication Systems

1. Which frequency range is used for TV transmission ?

(A) 30 HZ – 300 Hz

(B) 30 KHZ – 300 kHZ

(C) 30 MHz – 300 MHz

(D) 30 GHz – 300 GHZ

Answer : (C) 30 MHz – 300 MHz

1. Sky wave communication is based upon :

(A) reflection by ionosphere

(B) absorption by ionosphere

(C) transmission through ionosphere

(D) none of these

Answer : (A) reflection by ionosphere

1. The loss of strength of a signal while propagating though a medium is known as :

(A) reception

(B) absorption

(C) transmission

(D) attenuation

1. The process of increasing the strength of a signal using an electronic circuit is called :

(A) amplification

(B) modulation

(C) demodulation

(D) transmission

1. Modem is a device which performs :

(A) modulation

(B) demodulation

(C) rectification

(D) modulation and demodulation

Answer : (D) modulation and demodulation

1. The mode of propagation used by short wave broadcast services is :

(A) space wave

(B) sky wave

(C) ground wave

(D) both ‘A’ and ‘C’

1. Large bandwidth for higher data rate is achieved by using :

(A) high frequency carrier wave

(B) high frequency audio wave

(C) low frequency carrier wave

(D) low frequency audio wave

Answer : (A) high frequency carrier wave

1. Who invented world wide web?

(A) J.C.R. Licklider

(B) Tim Berners-Lee

(C) Alexander Graham Bell

(D) Samuel F.B. Morse

1. The device which is a combination of a receiver and a transmitter is :

(A) Amplifier

(B) Repeater

(C) Transducer

(D) Modulator

1. Which of the following is not a transducer ?

(A) Loudspeaker

(B) Amplifier

(C) Microphone

(D) All of these

1. Which of the following is an example of broadcast mode of communication?

(B) Television

(C) Mobile

(D) Both A and B

Answer : (D) Both A and B

1. The waves that are bent down by the ionosphere are:

(A) ground waves

(B) surface waves

(C) space waves

(D) sky waves

1. Who undertook the first space walk and in which year?

(A) Leonov, 1965

(B) Neil Armstrong, 1969

(C) Rakesh Sharma, 1998

(D) None of these

1. The term used to collect the information about an object and a place without physical contact” is called :

(A) modulation

(B) communication

(C) amplification

(D) remote sensing

1. The velocity of electromagnetic wave is :

(A) 3 x 109 ms-1

(B) 3 x 106 ms-1

(C) 3 x 108 ms-1

(D) 3 x 1010 ms-1

Answer : (C) 3 x 108 ms-1

1. From which layer of atmosphere are radio waves reflected ?

(A) Ionosphere

(B) Mesosphere

(C) Chromosphere

(D) None of the above

1. The modulation index in amplitude modulation :

(A) is always zero

(B) lies between 0 and 1

(C) lies between 1 and

(D) can never exceed 0.5

Answer : (B) lies between 0 and 1

1. The output of a digital computer is an example of :

(A) digital signal

(B) analog signal

(C) both (A) and (B)

(D) neither (A) nor (B)

1. Basically, a communication system is a :

(A) transmitter

(C) messenger

(D) All of these

Answer : (D) All of these

1. Present day communication systems are :

(A) electrical only

(B) electronic only

(C) optical only

(D) All of the above

Answer : (D) All of the above

1. Major parts of a communication system are :

(C) transmitter and communication channel

(D) transmitter, receiver and communication channel

1. Frequencies in the UHF range normally propagate by means of :

(A) Ground wave

(B) Sky waves

(C) Surface wave

(D) Space wave

1. The height of a TV transmission tower at any place on the surface of the earth is 245m. The maximum distance up to which transmission of tower will reach is :

(A) 245 m

(B) 245 km

(C) 56 km

(D) 112 km

1. Modulation is of:

(A) 2 types

(B) 3 types

(C) 4 types

(D) 5 types