JEE Main 2017 · 9 Apr · Shift 1 · Physics Q16

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A uniform wire of length l and radius r has a resistance of 100 Ω. It is recast into a wire of radius $\dfrac r2$ . The resistance of new wire will be :

1600 Ω

400 Ω

200 Ω

100 Ω

Answer and worked solution

Official answer: A

The volume is fixed, so halving the radius makes the length 4 times. $R\propto\dfrac l{r^2}$ grows by $4\times4=16$ : 1600 Ω.

Topics:Ohm's law and resistivity

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JEE Main 2017 · 9 Apr · Shift 1, Physics question 16