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CBSE Class 12 Physics 2020 Outside Delhi Set 2 Paper

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Question : 8
Total: 11
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 10V. If a current of 5A 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 Req
‌
1
R‌eq ‌
‌=‌
1
2
11
R
+‌
1
3
11
R
+‌
1
6
11
R
∴‌‌R‌eq ‌‌=‌
11
R
‌ Current ‌‌=I=5A
V‌=10V
Applying Ohm's law,
10‌=5×‌
11
R
∴‌‌R‌=5.5Ω
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