Calculating CRO wave frequency from visible cycles and time base

Steps:

• Time base setting is 10 ms/division; standard CRO screen spans 10 divisions, so total time = 100 ms = 0.1 s.
• From the diagram, the waveform completes 2.4 cycles across the full screen.
• Frequency f = number of cycles / total time = 2.4 / 0.1 = 24 Hz.

Why D is correct:

• Frequency f = 1/T, where T is period; equivalently, f = (cycles observed) / (total time), yielding 24 Hz for 2.4 cycles in 0.1 s.

Why the others are wrong:

• A: 0.24 Hz requires ~0.024 cycles in 0.1 s (period ~4 s), but diagram shows many more cycles.
• B: 4 Hz requires 0.4 cycles in 0.1 s (period 0.25 s), but diagram shows over twice that.
• C: 12 Hz requires 1.2 cycles in 0.1 s (period ~0.083 s), but diagram shows twice as many cycles.

Final answer: D