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A thin circular loop of area A is placed with its plane perpendicular to a uniform magnetic field of magnitude B. The loop is then cut at one point, and a galvanometer is connected across the gap so that the resistance of the complete circuit is R. If the loop is suddenly compressed until its area becomes zero, the total charge that passes through the galvanometer is
- BR/A
- AB/R
- ABR
- B²A²/R²
Correct answer: AB/R
Solution
q = d(Phi)/R = B*(A_final - A_initial)/R = B*A/R as the area collapses from A to 0.
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