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3. current electricity — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics3. current electricity1 Mark
MCQ
If a wire is stretched to make it $0.1 \%$ longer, its resistance will
  • A
    increase by $0.05 \% $ 
  • ✓
    increase by $0.2 \%$
  • C
    decrease by $0.2 \%$  
  • D
    decrease by $0.05 \% $
✓

Answer

Correct option: B.
increase by $0.2 \%$
b
Resistance of wire

$R=\frac{\rho l}{A}=\frac{\rho l^{2}}{C}(\text { where } A l=C)$

$\therefore $ Fractional change in resistance

$\frac{\Delta R}{R}=2 \frac{\Delta l}{l}$

$\therefore $ Resistance will increase by $0.2 \%$

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