Frequency from CRO Time Base

Steps:

• Identify the length of one complete wave cycle on the CRO screen: 4 cm.
• Convert to time using time base: 4 cm × 2.5 ms/cm = 10 ms (period T).
• Calculate frequency: f = 1/T = 1/0.01 s = 100 Hz.
• Match to choices: 100 Hz is option B.

Why B is correct:

• Frequency f = 1/T, where T is the period measured from the trace using the time base, yielding exactly 100 Hz for the given display.

Why the others are wrong:

• A: 50 Hz implies T=20 ms (8 cm), but trace shows 4 cm per cycle.
• C: 200 Hz implies T=5 ms (2 cm), but trace shows 4 cm per cycle.
• D: 400 Hz implies T=2.5 ms (1 cm), but trace shows 4 cm per cycle.

Final answer: B