Signals & Systems Multiple Choice Questions 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
Answer: C
Clarification: 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
Answer: B
Clarification: 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
Answer: B
Clarification: 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)
Answer: C
Clarification: 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
Answer: C
Clarification: 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
Answer: C
Clarification: 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
Answer: B
Clarification: 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
Answer: A
Clarification: 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 _______ 10. In discrete signal, if y [n] = x [k*n] and k>1 then ______
A. Compressed signal
B. Expanded signal
C. Time shifted signal
D. Amplitude scaled signal by factor 1/5
Answer: B
Clarification: y (t) = x (at), comparing this with the given expression we get a = 1/5. If 0
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