Frequency from CRO Period Measurement

Steps:

• Measure the screen distance for one complete signal cycle (4 cm).
• Calculate period T: 4 cm × 2.0 ms/cm = 8 ms = 0.008 s.
• Apply frequency formula: f = 1/T.
• Compute f = 1/0.008 = 125 Hz.

Why B is correct:

• 125 Hz matches f = 1/T, where T is the period derived from time-base scale (2.0 ms/cm) and cycle length.

Why the others are wrong:

• A: 50 Hz requires T = 20 ms (10 cm cycle), but trace shows 4 cm.
• C: 250 Hz requires T = 4 ms (2 cm cycle), but trace shows 4 cm.
• D: 500 Hz requires T = 2 ms (1 cm cycle), but trace shows 4 cm.

Final answer: B