Question 1
Comment on the periodicity of a constant signal?
A. It is periodic
B. It is not periodic
C. It is a mixture of period and aperiodic signal
D. It depends on the signal
View Answer
Answer: Option B
Explanation:
A constant signal is not periodic. It is because it does not repeat itself over in time. It is constant at any time, it is aperiodic.
Question 2
How can we generate a periodic signal from a periodic signal itself?
A. By extending a signal with duration T
B. Cannot be extended
C. By extending the periodic signal’s amplitude
D. By extending the sugar with duration 2π
View Answer
Answer: Option A
Explanation:
A periodic signal x(t) can be generated by a periodic extension of any segment of x of duration T( the period).As a result, we can generate x(t) from any segment x(t) having a duration of one period by replacing this segment and reproduction thereof end to end ad infinitum on either side.
Question 3
How is the period of the sum signal computed as?
A. T*n
B. T*T
C. T*N+M
D. T *(n+m)
View Answer
Answer: Option A
Explanation:
If a signal is periodic then we have to convert each of the periods to the ratio of integers. We have to take the ratio of greatest common divisor(gcd) from the numerator to the gcd of denominator. The LCM of the denominators of the resulting ratios is the value of n the period of the sum signal is T*n.
Question 4
Is a non periodic signal same as aperiodic signal?
A. No, it is not same as an aperiodic signal
B. Yes it is the other name of aperiodic signal
C. It is a branch of aperiodic signal
D. Aperiodic signal is a branch of non periodic signal
View Answer
Answer: Option B
Explanation:
A signal which does not satisfy the condition:x(t) = x(t+T) is called an aperiodic signal.Non periodic is another name of an aperiodic signal. Hence it is exactly the same.
Question 5
Is the signal eαt periodic?
A. Not periodic
B. Yes periodic
C. Depends on the value of
D. Semi- periodic
View Answer
Answer: Option C
Explanation:
Using the definition of x(t),x(t) = eαtejwt = ejwt+jwαTFor any value of α, if alpha is positive, it has a remaining term ejwαTHence it is not periodic.
Question 6
Is the sum of discrete time periodic signals periodic?
A. No, they are not
B. Yes they are
C. Depends on the signal
D. Not periodic if their ratio is not rational
View Answer
Answer: Option B
Explanation:
The sum of discrete time periodic signals always periodic because the period ratios N/N are always rational.For the continuous time, it depends on the ratio.
Question 7
Periodic signals actually exist according to a definition.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
Periodic signals are defined as signals having time period in between t=-∞ and t=+ ∞. These signals have an infinite time period that is periodic signals are continued forever. But real time signals always cease at some time due to distortion and resistance.
Question 8
Periodic signals are different in case of continuous time and discrete time signals.
A. TRUE
B. FALSE
View Answer
Answer: Option B
Explanation:
Periodic signals are same in case of continuous time and discrete time signals.In case of continuous time signal, x(t)=x(t+T), for all t>0In case of discrete time signal,x(n)=x(n+N), for all n>0.
Question 9
Under what conditions the three signals x(t), y(t) and z(t) with period t1 t2 and t3 respectively are periodic?
A. t1/t2= t2/t3
B. t1/t2 is rational
C. All the ratios of the three periods in any order is rational
D. t1/t2/t3= rational
View Answer
Answer: Option C
Explanation:
if x(t) , y(t) and z(t) are to be periodic then,t1/t2 should be rational and simultaneouslyt1/t3 should be rational andt2/t3 should be rational. Hence, all the ratios of the three periods in any order is rational.
Question 10
What are periodic signals?
A. The signals which change with time
B. The signals which change with frequency
C. The signal that repeats itself in time
D. The signals that repeat itself over a fixed frequency
View Answer
Answer: Option C
Explanation:
Those signals which repeat themselves in a fixed interval of time are called periodic signals. The continuous-time signal x(t) is periodic if and only ifx(t+T)= x(t).
Question 11
What is a fundamental angular frequency?
A. The inverse of the fundamental time period
B. The inverse of fundamental frequency
C. Fundamental frequency in radians
D. Fundamental frequency in degree
View Answer
Answer: Option C
Explanation:
The inverse of the fundamental time period is called fundamental frequency. If it is F, then 2πF is called the fundamental angular frequency ie it is a fundamental frequency in radians.
Question 12
What is a fundamental period?
A. Every interval of a periodic signal
B. Every interval of an aperiodic signal
C. The first interval of a periodic signal
D. The last interval of a periodic signal
View Answer
Answer: Option C
Explanation:
The first time interval of a periodic signal after which it repeats itself is called a fundamental period. It should be noted that the fundamental period is the first positive value of frequency for which the signal repeats itself.
Question 13
What is the area of a periodic signal in a periodic interval?
A. It depends on the situation
B. It is same as the area in the previous interval
C. It is different in different situations
D. It is the square of the fundamental period
View Answer
Answer: Option B
Explanation:
The area of any periodic signal in any interval is the same. Hence it is same as the previous interval. This results from the fact that a periodic signal takes same values at the intervals of T.
Question 14
What is the fundamental period of the signal : ejwt?
A. 2π/w
B. 2π/w2
C. 2π/w3
D. 4π/w
View Answer
Answer: Option A
Explanation:
The complex exponential signal can be represented asejwt= ejwt+jwTHence, wt=2 π,T= 2π/w.
Question 15
What is the general range of a period of a signal?
A. It can have of any value from positive to negative
B. It can be negative
C. It can be positive
D. It is always positive
View Answer
Answer: Option D
Explanation:
The period of a periodic signal is always positive. The smallest positive value of a periodic interval is called a fundamental period in case of both discrete and continuous time signal.
Question 16
What is the necessary and sufficient condition for a sum of a periodic continuous time signal to be periodic?
A. Ratio of period of the first signal to period of other signals should be constant
B. Ratio of period of the first signal to period of other signals should be finite
C. Ratio of period of the first signal to period of other signals should be real
D. Ratio of period of first signal to period of other signal should be rational
View Answer
Answer: Option D
Explanation:
The necessary and sufficient condition for a sum of a periodic continuous time signal to be periodic is that the ratio of a period of the first signal to the period of other signals should be rational.I.e T/Ti = a rational number.
Question 17
What is the period of cos3t + sin14t?
A. 4π
B. π
C. 2π
D. 3π
View Answer
Answer: Option B
Explanation:
We know, T1= 2 π/3 and T2= 2 π/14Now, T1/T2=14/3.
Question 18
What is the period of the signal :jejw11t?
A. 2π/10
B. 2π/11
C. 4π/10
D. 4π/11
View Answer
Answer: Option B
Explanation:
From the definition of periodic signal, we express a periodic exponential signal as :ejw11t= ejwt+jwTHence, 11wt=2 π,which gives the fundamental period as2π/11.
Question 19
What is the time period of a periodic signal in actual terms?
A. The signals which start at t=-∞ and end at t=+∞
B. The signals which have a finite interval of occurrence
C. The signals which start at t= -∞ and ends at a finite time period
D. The signals which have a short period of occurrence
View Answer
Answer: Option A
Explanation:
The periodic signals have actually a time period between t=-∞ and at t= + ∞. These signals have an infinite time period, that is periodic signals are actually continued forever. But this is not possible in case of real time signals.
Question 20
When a continuous signal is a mixture of two continuous periodic signals, what is its periodicity?
A. LCM of the periods of the two signals, provide their ratio is unity
B. LCM of the periods of the two signals, provide their ratio is rational
C. HCF of the periods of the two signals, provide their ratio is rational
D. LCM of the periods of the two signals provide their ratio is real
View Answer
Answer: Option B
Explanation:
When a continuous signal is a mixture of two continuous periodic signals if their time periods are T1 and T2, and their ratio is rational number, then, the periodicity of the continuous time signal will be the LCM of T1 and T2.
Question 21
When is the sum of M periodic signals periodic?
A. T/Ti = 1
B. T/Ti = 4
C. T/Ti = ni
D. T/Ti = m+n
View Answer
Answer: Option C
Explanation:
The sum of M periodic signal is not necessarily periodic. It is periodic only with the condition thatT/Ti = ni, 1≤i≤M,where Ti is the period of the signal and in the sum of ni is an integer.