Frequency from CRO waveform period

Steps:

• Measure divisions for one complete cycle on the waveform: 2.8 divisions.
• Calculate period T = 2.8 × 5.0 ms/div = 14 ms = 0.014 s.
• Compute frequency f = 1 / T = 1 / 0.014 s ≈ 71 Hz.

Why B is correct:

• Frequency formula f = 1/T gives 71 Hz when T = 0.014 s from the time-base and measured divisions.

Why the others are wrong:

• A: 57 Hz implies T ≈ 17.5 ms (3.5 div), exceeds measured 2.8 div.
• C: 114 Hz implies T ≈ 8.8 ms (1.76 div), less than measured 2.8 div.
• D: 143 Hz implies T ≈ 7.0 ms (1.4 div), much less than measured 2.8 div.

Final answer: B