Effect of rotation speed on AC waveform period

Steps:

• AC generator frequency equals rotation speed in cycles per second.
• Slowing rotation decreases frequency, increasing the waveform period.
• Oscilloscope time base unchanged, so decreased frequency stretches the waveform horizontally across the screen.
• Amplitude remains the same as voltage output is unaffected by speed alone.

Why B is correct:

• B shows a stretched sine wave with longer period, directly following the inverse relationship between frequency and period (T = 1/f).

Why the others are wrong:

• A: Unchanged waveform, ignores frequency decrease.
• C: Compressed waveform, implies increased frequency.
• D: Altered amplitude, but speed affects only period, not peak voltage.

Final answer: B