Question
A magstripe reader used to read a credit card number or a card key for a hotel room has a tiny coil that detects a changing magnetic field as tiny bar magnets pass by the coil. Calculate the magnitude of the induced emf in a magstripe card reader coil. Assume that the magstripe magnetic field changes at a constant rate of $500 \mathrm{mT} / \mathrm{ms}$ as the region between two tiny magnets on the stripe passes the coil. The reader coil is $2.0 \mathrm{mm}$ in diameter and has 5000 turns.
Step 1
Given that $1 \mathrm{mT} = 10^{-3} \mathrm{T}$ and $1 \mathrm{ms} = 10^{-3} \mathrm{s}$, we have \[ \frac{dB}{dt} = 500 \mathrm{mT/ms} = 500 \times 10^{-3} \mathrm{T/s} = 500 \mathrm{T/s}. \] Show more…
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