Frequency from CRO Period Measurement

Steps:

• Measure the period T: one complete wave on the trace spans 4 divisions.
• Time per division is 0.2 ms, so T = 4 × 0.2 ms = 0.8 ms.
• Convert T to seconds: 0.8 ms = 8 × 10^{-4} s.
• Calculate frequency f = 1/T = 1/(8 × 10^{-4}) = 1250 Hz.

Why B is correct:

• Frequency equals the reciprocal of the period, directly computed from the time base and waveform span per the oscilloscope's time-to-voltage conversion.

Why the others are wrong:

• A: 1000 Hz implies T = 1 ms (5 divisions), but trace shows 4 divisions.
• C: 2000 Hz implies T = 0.5 ms (2.5 divisions), but trace shows 4 divisions.
• D: 2500 Hz implies T = 0.4 ms (2 divisions), but trace shows 4 divisions.

Final answer: B