JEE Main 2022 · 30 Jun · Shift 1 · Physics Q45

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PhysicsSingle correct+4 / -1Question 45 of 90

An electric cable of copper has just one wire of radius 9 mm. Its resistance is 14 $\Omega$ . If this single copper wire of the cable is replaced by seven identical well insulated copper wires each of radius 3 mm connected in parallel, then the new resistance of the combination will be :

\Omega

\Omega

\Omega

126

\Omega

Answer and worked solution

Official answer: B

Area. One wire $81\pi$ , seven wires $63\pi$ mm². $R\propto\frac1A$ : $14\times\frac{81}{63}=18$ Ω.

(B)

Topics:Ohm's law and resistivity

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JEE Main 2022 · 30 Jun · Shift 1, Physics question 45