Doubling rotation speed doubles induced EMF frequency.

Steps:

• Oscilloscope trace shows sinusoidal induced EMF from coil rotation in magnetic field.
• Faraday's law states induced EMF depends on flux change rate, producing AC waveform at rotation frequency.
• Original trace frequency matches initial rotation speed.
• Doubling speed doubles flux change cycles per second, doubling waveform frequency.

Why B is correct:

• B depicts waveform with twice the cycles in the same time, matching doubled rotation frequency per Faraday's law.

Why the others are wrong:

• A: Same frequency as original, ignores speed effect.
• C: Halved frequency, contradicts speed increase.
• D: Same frequency but altered amplitude, but amplitude unchanged while frequency doubles.

Final answer: B