Concept:Faraday's Law of Electromagnetic Induction calculates the average induced EMF based on the rate of change of magnetic flux.
Formula:$$ \varepsilon = -N \frac{\Delta \phi}{\Delta t} $$
Solution:- Given: Number of turns \( N = 100 \).
- Initial flux \( \phi_i = 20 \text{ mWb} \). Because it is "reversed", the final flux is \( \phi_f = -20 \text{ mWb} \).
- Change in flux: \( \Delta \phi = \phi_f - \phi_i = -20 - 20 = -40 \text{ mWb} = -40 \times 10^{-3} \text{ Wb} \).
- Time interval \( \Delta t = 2 \text{ ms} = 2 \times 10^{-3} \text{ s} \).
- Substitute values into the formula:
$$ \varepsilon = -100 \times \frac{-40 \times 10^{-3}}{2 \times 10^{-3}} $$
- Simplify:
$$ \varepsilon = 100 \times \frac{40}{2} = 100 \times 20 = 2000 \text{ V} $$
Why other options are incorrect:A common mistake is failing to realize that "reversed" means moving from \( +20 \) to \( -20 \) (a total change of \( 40 \)), not just dropping to zero. Using \( 20 \) instead of \( 40 \) leads to the incorrect answer of 1000 V.
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