CBSE Class 12 Physics 2020 Outside Delhi Set 2 Paper

Question : 8 of 11

Marks: +1, -0

SECTION - B

A uniform wire is cut into three parts with their lengths in the ratio

2: 3: 6

. The ends of each of these three parts are connected across an ideal battery of

10 {\V}

. If a current of

5 {\A}

is drawn from the battery, find the initial resistance of the wire.

Solution:

Consider that the resistance of a wire is

{\R}

So, the resistance of the three parts are

\;{2}/{11} R, \;{3}/{11} R

and

\;{6}/{11} R

, respectively.
They are now connected in parallel combination across a source of voltage.
So, the equivalent resistance

R_{ {\eq}}

\;{1}/{R_{\;\text "eq "\;}}\;=\;{1}/{{2}/{11} R}+\;{1}/{{3}/{11} R}+\;{1}/{{6}/{11} R}

∴ \;\; R_{\;\text "eq "\;}\;=\;{11}/{R}

\;\text " Current "\;\;=I=5 {\A}

V\;=10 {\V}

Applying Ohm's law,

10\;=5 × \;{11}/{ {\R}}

∴ \;\; {\R}\;=5.5 Ω

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