Current Electricity and Electrical InstrumentMedium
Question
A wire of radius r has resistance R. If it is stretched to a radius 
, its resistance will be :
, its resistance will be :Options
A.16 R
B.2 R
C.4 R
D.zero
Solution
Let length & cross sectional area of wire be l &a respectively. ρ br the specific resistance, then
R = ρ
If radius becomes half, area becomes
th or cross sectional area after4 the stretch 
.
Let its legth increases to l′. Since volume remains the same in the process,
l a = l′ × ⇒ l′ = 4l
Let R′ be the resistance of streched wire
R′ = ρ ×
= 16 × ρ 
16 R
R = ρ
If radius becomes half, area becomes
th or cross sectional area after4 the stretch .Let its legth increases to l′. Since volume remains the same in the process,
l a = l′ ×
⇒ l′ = 4l Let R′ be the resistance of streched wire
R′ = ρ ×
= 16 × ρ 16 RCreate a free account to view solution
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