Time-base setting from wave frequency and screen distance

Steps:

• Calculate period T = 1/f = 1/270 ≈ 0.0037 s for the 270 Hz wave.
• Observe waveform: approximately 2.7 cycles across 10 cm screen width.
• Total time for 10 cm = number of cycles × T = 2.7 × 0.0037 s = 0.01 s.
• Time per cm = 0.01 s / 10 cm = 0.001 s/cm = 1 ms/cm.

Why B is correct:

• 1 cm^{-1} equals 1 ms/cm, matching the calculated time per cm from frequency and observed cycles via T = 1/f.

Why the others are wrong:

• A: 0.1 cm^{-1} = 0.1 ms/cm yields ~27 cycles in 10 cm, but waveform shows fewer.
• C: 10 cm^{-1} = 10 ms/cm yields ~0.27 cycles in 10 cm, but waveform shows more.
• D: 100 cm^{-1} = 100 ms/cm yields ~0.027 cycles in 10 cm, too few for visible waves.

Final answer: B