Free Objective Test 01 Practice Test - 11th and 12th
Question 1
In which of the following remote sensing technique is not used
SOLUTION
Solution : D
Remote sensing is the technique to collect information about an object in respect of its size, colour, nature, location, temperature etc. without physically touching it. There are some areas or location which are inaccessible. So to explore these areas or locations, a technique known as remote sensing is used. Remote sensing is done through a satellite.
Question 2
Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion : Television signals are received through sky-wave propagation.
Reason : The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.
SOLUTION
Solution : D
TV signals (frequency greater than 30 MHz) cannot be propagated through sky wave propagation.
Above critical frequency, an electromagnetic wave penetratates the ionosphere and is not reflected by it.
Question 3
Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion :The electromagnetic waves of shorter wavelength can travel longer distances on earth's surface than those of longer wavelengths.
Reason : Shorter the wavelength, the larger is the velocity of wave propagation.
SOLUTION
Solution : C
The electromagnetic waves of shorter wavelength do not suffer much diffraction from the obstacles of earth's atmosphere so they can travel long distance.
Also, shorter the wavelength, shorter is the velocity of wave propagation.
Question 4
The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantisation levels have been used is
SOLUTION
Solution : A
If n is the number of bits per sample, then number of quantisation level = 2n
Since the number of quantisation level is 16
⇒2n=16⇒ n = 4
∴ bit rate = sampling rate × no.of bits per sample
= 8000 × 4 = 32,000 bits/sec
Question 5
If fa and ff represent the carrier wave frequencies for amplitude and frequency modulations respectively, then
SOLUTION
Solution : B
fa < ff
Question 6
The frequency of a FM transmitter without signal input is called
SOLUTION
Solution : C
The frequency of a FM transmitter without signal input is called Resting frequency
Question 7
Indicate which one of the following system is digital?
SOLUTION
Solution : B
Pulse code modulation is a digital system.
Question 8
The waves used in telecommunication are?
SOLUTION
Solution : C
In telecommunication, microwaves are used.
Question 9
The modulation index of an FM carrier having a carrier swing of 200 kHz and a modulating signal 10 kHz is
SOLUTION
Solution : B
CS = 2 ×△f or △f=CS2
∴△f=2002 = 100kHz
Now mf = △ffm=10010=10
Question 10
In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is
SOLUTION
Solution : A
Carrier swing = Frequency deviationModulating frequency=507 = 7.143
Question 11
The electromagnetic waves of frequency 2 MHz to 30 MHz are
SOLUTION
Solution : B
The EM waves of frequency from 2MHz to 30 MHz are reflected from the ionized upper layers of earth's atmosphere and hence the sky wave propagation
Question 12
Sinusoidal carrier voltage of frequency 1.5 MHz and amplitude 50 V is amplitude modulated by sinusoidal voltage of frequency 10 kHz producing 50% modulation. The lower and upper side-band frequencies in kHz are
SOLUTION
Solution : A
Here, fc = 1.5 MHz = 1500 kHz ,fm = = 10 kHz
∴ Low side band frequency
= fc - fm = 1500 kHz - 10 kHz = 1490 kHz
Upper side band frequency
= fc + fm = 1500 kHz + 10 kHz = 1510 kHz
Question 13
Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion: Short wave bands are used for transmission of radio waves to a large distance.
Reason : Short waves are reflected by ionosphere
(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 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 assertion is false but reason is true.
SOLUTION
Solution : A
Having the range of wavelength from 30 km to 30 cm are known as short wave. These waves are used for radio transmission and for general communication purpose to a longer distance from ionosphere. Ionosphere is the outermost region of atmosphere extending from height of 80 km to 400 km approximately, above the surface of earth. Therefore, both the assertion and reason are true and reason is the correct explanation of assertion.
Question 14
Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion : The electrical conductivity of earth's atmosphere decreases with altitude.
Reason : The high energy particles (i.e. g-rays and cosmic rays) coming from outer space and entering our earth's atmosphere cause ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.
(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 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 assertion is false but reason is true.
SOLUTION
Solution : E
The electrical conductivity of earth's atmosphere increases with height so assertion is false.
When high energy particles enters in earth's atmosphere. They ionises the gases present in atmosphere. Also as we go up, the air thins out gradually and air pressure decreases.
Question 15
An amplitude modulated wave is modulated to 50%. What is the saving in power if carrier as well as one of the side bands are suppressed
SOLUTION
Solution : C
Psb = Pc(ma2)2 = Pc(0.52)4=0.0625Pc
Also P = Pc(1+ma22)=Pc(1+(0.5)22)=1.125Pc
∴ % saving = (1.125Pc−0.0625Pc)1.125Pc×100 = 94.4%