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NEET 2006 (AIPMT) · Biot-Savart Law & Circular Coils

Biot-Savart Law & Circular Coils question from NEET 2006 (AIPMT)

Q104NEET 2006 · AIPMTMedium

Biot-Savart Law & Circular Coils

Two circular coils 1 and 2 are made from the same wire but the radius of the 1st coil is twice that of the 2nd coil. What ratio of potential difference in volts should be applied across them so that the magnetic field at their centres is the same?

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Answer: (c)

Equal field $\frac{\mu_0 I}{2r}$ at the centres needs $I \propto r$ .
Same wire: resistance $\propto$ circumference $\propto r$ .
$V = IR \propto r^2 \Rightarrow \frac{V_1}{V_2} = 2^2 = 4$
So the answer is (c) 4.

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