Time-base adjustment compresses the waveform horizontally

Steps:

• Original time-base of 4 ms/cm means 4 milliseconds per centimeter on screen.
• New setting of 2 ms/cm halves the time per centimeter, speeding up the sweep.
• Same screen width now displays half the original time duration.
• Periodic waveform appears compressed, showing more cycles or narrower peaks.

Why C is correct:

• Option C depicts a horizontally compressed trace, matching the definition of time-base as time per division—reducing it from 4 ms/cm to 2 ms/cm halves horizontal scale per the oscilloscope sweep rate formula.

Why the others are wrong:

• A shows unchanged trace, ignoring time-base effect.
• B shows stretched trace, which occurs if time-base increases.
• D shows altered amplitude or shape, unrelated to time-base.

Final answer: C