Question Details

Consider the system as shown below

where, y(t)=x(et). The system is

Options

A

non-linear and causal.

B

linear and non-causal.

C

non-linear and non-causal.

D

linear and causal.

Show Answer

Correct Answer :

Option B

linear and non-causal.

Solution :

The correct option is linear and non-causal.

Given the block diagram representing a system with input x(t) and output y(t):

The input-output relationship of the system is given by:
y(t)=x(et)
To determine the characteristics of the system, we analyze both its linearity and its causality.

1. Linearity Test:
A system is linear if it satisfies the principle of superposition (homogeneity and additivity).
Let y1(t) be the output corresponding to an input x1(t):
y1(t)=x1(et)
Let y2(t) be the output corresponding to another input x2(t):
y2(t)=x2(et)
Now, let us apply a linear combination of the two inputs as the new input, x3(t)=ax1(t)+bx2(t), where a and b are constants.
The corresponding output y3(t) is:
y3(t)=x3(et)=ax1(et)+bx2(et)
Substituting the expressions for y1(t) and y2(t), we get:
y3(t)=ay1(t)+by2(t)
Since the system satisfies the superposition principle, it is linear.

2. Causality Test:
A system is causal if the output at any time t depends only on present and/or past values of the input. If the output depends on any future values of the input, the system is non-causal.
Let us evaluate the output at a few specific time instants:
For t=0:
y(0)=x(e0)=x(1)
Here, the output at t=0 depends on the input at the future time t=1.
For t=2:
y(2)=x(e2)x(7.39)
Here, the output at t=2 depends on the input at the future time t7.39.
Since the output depends on future values of the input (because et>t for all real t), the system is non-causal.

Conclusion:
The system is both linear and non-causal.

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