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Class 12 › Physics › Current Electricity
CBSE2022Class Class 12 · Physics3 Marks · Short✅ Verified
A coil contains $N$ turns of insulated copper wire of diameter $d$ and resistivity $\rho$ wound on a cylinder of diameter $D$. What is the total resistance between the two ends of the coil? (Given: $D \gg d$)
✅ Answer & Solution
Length per turn $= \pi D$, total length $L = N\pi D$
Cross-sectional area of wire $A = \pi d^2/4$
$$R = \frac{\rho L}{A} = \frac{\rho \cdot N\pi D}{\pi d^2/4} = \frac{4N\rho D}{d^2}$$
