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CBSE Class 12 Physics 2023 Outside Delhi Set 3 Paper

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Question : 12
Total: 13
A potential difference V is applied across a conductor of length l and cross-sectional area A. Briefly explain how the current density j in the conductor will be affected if
(a) the potential difference V is doubled. reduce
(b) the conductor were gradually stretched to its cross- sectional area to ‌
A
2
 and then the same potential difference V is applied across it.
Solution:     👈: Video Solution
Initial current =I=‌
V
R
=‌
V
ρ⋅‌
L
A
=‌
VA
ρL

Initial current density =J=‌
V
ρL

(a) Final current density =J′=‌
2V
ρL
=2J
So the current density becomes double.
(b) When area of cross section becomes ‌
A
2
,
The length becomes 2L.
So, final current density =J′′=‌
V
ρL′

J′′=‌
V
2ρL
=‌
1
2
J
So, the current density becomes half
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