The resistance of a wire is R . It is bent at the middle by 180^ ^ and both the ends are twisted together to make a shorter wire. The resistance of the new wire is

Correct answer: C. R / 4 Resistance of wire (R)= (l)/(A) If wire is bent in the middle then l^ = (l)/(2), A^ =2 A New resistance, R^ = l^ A^ =( (l)/(2))/(2 A)=( l)/(4 A)=(R)/(4)

BITSAT 2015

Exam: BITSAT
Year: 2015
Subject: Physics
Chapter: Current Electricity

BITSAT 2015 · Physics · Current Electricity

The resistance of a wire is R . It is bent at the middle by 180^ ^...

The resistance of a wire is

R

. It is bent at the middle by

180^{{}^{\circ}}

and both the ends are twisted together to make a shorter wire. The resistance of the new wire is

Options

A $2 R$
B $R / 2$
C $R / 4$
D $R / 8$

Correct answer

C. $R / 4$

Step-by-step solution

Resistance of wire

(R)=\rho \frac{l}{A}

If wire is bent in the middle then l^{\prime}=

\frac{l}{2},

A^{\prime}=2 A

\therefore

New resistance,

\mathrm{R}^{\prime}=\rho \frac{l^{\prime}}{\mathrm{A}^{\prime}}=\frac{\rho \frac{l}{2}}{2 A}=\frac{\rho l}{4 A}=\frac{R}{4}

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