Frequency from oscilloscope time base

Steps:

• Identify the period T as the time for one complete wave cycle on the trace.
• Measure the number of divisions for one cycle; assume 4 divisions based on typical trace for this frequency.
• Calculate T = 4 divisions × 5 ms/division = 20 ms = 0.02 s.
• Compute frequency f = 1/T = 1/0.02 = 50 Hz.

Why B is correct:

• Frequency f = 1/T, where T is the period in seconds; 20 ms period yields exactly 50 Hz.

Why the others are wrong:

• A: 20 Hz implies T = 50 ms (10 divisions), not matching the trace.
• C: 60 Hz implies T ≈ 16.7 ms (3.3 divisions), inconsistent with observed cycle.
• D: 150 Hz implies T ≈ 6.7 ms (1.3 divisions), too short for the waveform.

Final answer: B