A constant voltage is applied between the two ends of a uniform metallic wire, heat H is developed in it. If another wire of the same material, double the radius and twice the length as compared to original wire is used then the heat developed in it will be :
Resistance R∝ l/A , and for the new wire, R′ = R/4.Heat H ∝
1/R , so H′ = 4H.
Answer: (d) 4H.
Class 12th Science Physics NCERT MCQ Questions
NCERT Books MCQ Questions Session 2024-2025.
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The heat developed in a wire is given by H = V²t / R. Resistance R is given by R = ρL/A.For the new wire:
Length (L’) = 2L,
Radius (r’) = 2r, so A’ = 4A,
R’ = (ρ × 2L) / (4A) = R/2.
Since H ∝ 1/R, the heat developed H’ = 2H.
Thus, the correct answer is (c) 2H.
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