JEE MainPhysicsCurrent ElectricityMCQ+4 / −1
A wire of resistance R1 is drawn out so that its length is increased by twice of its original length. The ratio of new resistance to original resistance is :
- A9 : 1
- B1 : 9
- C4 : 1
- D3 : 1
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Correct answer: A
-
Use the resistance formula
For a wire, where:
- = resistivity (constant for same material)
- = length
- = cross-sectional area
-
Interpret the statement
“Its length is increased by twice of its original length” means the new length becomes:
-
Use conservation of volume
When a wire is drawn out, its volume remains constant:
Since ,
-
Find the new resistance
Original resistance:
New resistance:
-
Compute the ratio
-
Check options
- A: ✅
- B: ❌
- C: ❌
- D: ❌
Therefore, the correct answer is A.
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