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A wire of resistance 4 Omega is used to ...

A wire of resistance `4 Omega` is used to wind a coil of radius 7 cm. The wire has a diameter of 1.4 mm and the specific resistance of its material is `2xx10^(-7) Omega m`. Find the number of turns in the coil.

A

50

B

40

C

60

D

70

Text Solution

Verified by Experts

The correct Answer is:
D
Let n be the number of turns in the coil.
Then the total length of wire used. `l=2pir xx n=2pixx7xx10^(-2)xxn`
Total resistance, `R=rho(l)/(A)`
or `4=(2xx10^(7)xx2pixx7xx10^(-2)xxn)/(pi(0.7xx10^(-3))^(2))therefore n=70`
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