Question

a wire of resistance 1 Om is stretched so as to change its diameter by 0.25 %.the percentage change in its resistance is
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Answer 1

Answer:

R = ρ X L / A - [1]

WHEN THE WIRE is stretched its volume is constant

since volume is constant and question is based on diameter multiply both numerator and denominator with A so the formula will be R = ρ x v / A^2

v is volume = A x L

so R is inversely proportional to A^2 area = pi x d^2/4

so R is inversely proportional to d^4

so, percentage change in its resistance ΔR x 100 / R = 4 x Δd x 100 / d

but given that Δd x 100 / d = 0.25 %

so ΔR x 100 / R  = 4 x 0.25 % = 1 %