This set of Signals & Systems Multiple Choice Questions & Answers (MCQs) focuses on “Basic Operations on Signals – 1”.

1. Which of the following is an example of amplitude scaling?

a) Electronic amplifier

b) Electronic attenuator

c) Both amplifier and attenuator

d) Adder

View Answer

Explanation: Amplitude scaling refers to multiplication of a constant with the given signal.

It is given by y (t) = a x (t). It can be both increase in amplitude or decrease in amplitude.

2. Resistor performs amplitude scaling when x (t) is voltage, a is resistance and y (t) is output current.

a) True

b) False

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Explanation: The given statement is not true. The relation between voltage, current and resistance is given by V = IR. Comparing with equation y (t) = a x (t), we can see that y (t) is the output voltage for given current x (t) with resistance R.

3. Which of the following is an example of physical device which adds the signals?

a) Radio

b) Audio mixer

c) Frequency divider

d) Subtractor

View Answer

Explanation: Audio mixer is a device which combines music and voice signals. It is given by

Y (t) = x1 (t) + x2 (t).

4. AM radio signal is an example for __________

a) y (t) = a x (t)

b) y (t) = x1 (t) + x2 (t)

c) y (t) = x1 (t) * x2 (t)

d) y (t) = -x(t)

View Answer

Explanation: AM radio signal is an example for y (t) = x1 (t) * x2 (t) where, x1 (t) consists of an audio signal plus a dc component and x2 (t) is a sinusoidal signal called carrier wave.

5. Which of the passive component performs differentiation operation?

a) Resistor

b) Capacitor

c) Inductor

d) Amplifier

View Answer

Explanation: Inductor performs differentiation. It is given by y (t) = L d/dt i(t) where, I (t) denotes current flowing through an inductor of inductance L.

6. Which of the component performs integration operation?

a) Resistor

d) Diode

c) Capacitor

d) Inductor

View Answer

Explanation: Capacitor performs integration. V (t) developed across capacitor is given by

v (t) = (1/C)* ∫

^{t}

_{-∞}i (∂).d∂, I (t) is the current flowing through a capacitor of capacitance C.

7. Time scaling is an operation performed on _______

a) Dependent variable

b) Independent variable

c) Both dependent and independent variable

d) Neither dependent nor independent variable

View Answer

Explanation: Time scaling is an example for operations performed on independent variable time.

It is given by y (t) = x (at).

8. Y (t) = x (2t) is ________

a) Compressed signal

b) Expanded signal

c) Shifted signal

d) Amplitude scaled signal by a factor of 2

View Answer

Explanation: By comparing the given equation with y (t) = x (at) we get a=2. If a>1 then it is compressed version of x (t).

9. Y (t) = x (t/5) is _______

a) Compressed signal

b) Expanded signal

c) Time shifted signal

d) Amplitude scaled signal by factor 1/5

View Answer

Explanation: y (t) = x (at), comparing this with the given expression we get a = 1/5. If 0<a<1 then it is expanded (stretched) version of x (t).

10. In discrete signal, if y [n] = x [k*n] and k>1 then ______

a) Some samples are lost from x [n]

b) Some samples are added to x [n]

c) It has no effect on samples

d) Samples will be increased with factor k

View Answer

Explanation: For discrete time signal y [n] = x [k*n] and k>1, it will be compressed signal and some samples will be lost. The samples lost will not violate the rules of sampling theorem.

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