This question was asked inGPSC AE (Electrical) Class-2 R&B Department Paper 2025 – Series MQuestion 69 of 179 published · Gujarat Public Service CommissionOpen paper
Q179EasySignals & Classification

Determine the discrete−time signal: x(n) = 1 for n ≥ 0 and x(n) = 0 for n < 0.

Answer & step-by-step solution
Correct answer: D. Unit step sequence
Quick explanation

The sequence defined as 1 for n≥0 and 0 for n<0 is the discrete-time unit step u[n]. It switches from 0 to 1 at n=0 and remains at 1 thereafter.

u[n] = {1, n ≥ 0 δ[n] = u[n] − u[n−1]

Concept & Reasoning

The unit impulse δ[n] is nonzero only at n=0, whereas the unit step u[n] remains one for all nonnegative n. A unit ramp grows with n. These distinctions are fundamental in convolution and system-response problems.

How to Solve It in the Exam

One at and after zero → unit step.

Important Exam Point

Use δ[n] only for a single non-zero sample at n=0.

Quick Trick

One at and after zero → unit step.

Common Mistake

Confusing unit step with unit impulse.

Solution diagram – Determine the discrete−time signal: x(n) = 1 for n ≥ 0 and x(n) = 0 for n < 0.
Exam tipUse δ[n] only for a single non-zero sample at n=0.
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