GATE IN topic:communication-optical-instrumentation PYQs & Answers — Page 2

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topic:communication-optical-instrumentation

Questions 11–20 of 34. Imported answers require independent review unless marked reviewed.

Topic practice 34 questionsPage 2 of 4

A sinusoidal carrier wave with amplitude

and frequency

is amplitude modulated with a message signal

having frequency

to generate the modulated wave

given by

The message signal that can be retrieved completely using envelope detection is ______

Your answerChoose one option.

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Consider 24 voice signals being transmitted without latency using time-division multiplexing. If each signal is sampled at 12 kHz and represented by an 8-bit word, the bit-duration (in microseconds) is ______ (round off to two decimal places)

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A photodiode is made of a semiconductor with a bandgap of 1.42 eV. Given that Planck’s constant is

Js, the speed of light in vacuum is

m/s, and 1 eV =

J, the cut-off wavelength (in nanometers) of the photodiode is ______ (round off to one decimal place)

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An amplitude modulation (AM) scheme uses tone modulation, with modulation index of 0.6. The power efficiency of the AM scheme is ____ % (rounded off to one decimal place).

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When the movable arm of a Michelson interferometer in vacuum (

) is moved by 325

m, the number of fringe crossings is 1000. The wavelength of the laser used in nanometers is _____.

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A signal having a bandwidth of 5 MHz is transmitted using the Pulse code modulation (PCM) scheme as follows. The signal is sampled at a rate of 50% above the Nyquist rate and quantized into 256 levels. The binary pulse rate of the PCM signal in Mbits per second is ___.

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In the figure shown, a large multimode fiber with

and

is used for sensing. A portion with the cladding removed passes through a liquid with refractive index

. An LED is used to illuminate the fiber from one end and a paper is placed on the other end, 1 cm from the end of the fiber. The paper shows a spot with radius 1 cm. The refractive index

of the liquid (rounded off to two decimal places) is __________.

Diagram for Instrumentation Engineering question 55

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A sinusoid of 10 kHz is sampled at 15 k samples/s. The resulting signal is passed through an ideal low pass filter (LPF) with cut-off frequency of 25 kHz. The maximum frequency component at the output of the LPF (in kHz) is ____.

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A laser beam of 10 mm beam diameter is focused onto an optical fibre using a thin biconvex lens as shown in the figure. The refractive index of the lens is 1.5. The refractive indices of the core and cladding of the fibre are 1.55 and 1.54 respectively. The minimum value of the focal length of the lens to attain the maximum coupling to the fibre (in mm, rounded off to one decimal place) is ____

Diagram for Instrumentation Engineering question 46

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As shown in the figure, a slab of finite thickness

with refractive index

, has air (

) above and below it. Light of free space wavelength 600 nm is incident normally from air as shown. For a destructive interference to be observed at R, the minimum value of thickness of the slab

(in nm) is ____

Diagram for Instrumentation Engineering question 47

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GATE IN topic:communication-optical-instrumentation PYQs

Question 16

Question 26

Question 27

Question 21

Question 22

Question 54

Question 55

Question 22

Question 46

Question 47