Induced EMF Changes Due to Coil Length and Magnet Polarity

Steps:

• Identify that traces show induced EMF from changing magnetic flux as magnet passes through coil (Faraday's law).
• Note original trace: same pole enters, standard flux direction and coil length set peak duration.
• Compare new trace: differences in peak width (duration) and polarity (inversion) indicate coil length and pole changes.
• Match to option: longer coil extends flux change time; opposite pole reverses field direction, inverting trace.

Why A is correct:

• Longer coil increases time for flux change, broadening trace; opposite pole reverses B-field direction, inverting EMF sign per Lenz's law.

Why the others are wrong:

• B: Shorter coil narrows trace, not broadens; opposite pole inverts but doesn't match observed difference.
• C: Shorter coil narrows trace; same pole keeps polarity, no inversion.
• D: Longer coil broadens trace but same pole retains polarity, no inversion.

Final answer: A