Physics · Series and parallel combinations of resistors, temperature dependence of resistance
The resistance of an iron wire is and its temperature coefficient of resistance
The resistance of an iron wire is \( 10 \Omega \) and its temperature coefficient of resistance is \( 5 \times 10^{-3} /^{o} C . \) A current of \( 30 \mathrm{mA} \) is flowing in it at \( 20^{\circ} \mathrm{C} \). Keeping potential difference across its ends constant, if its temperature is increased to \( 120^{\circ} \mathrm{C} \) then the current flowing in the wire will be (in \( \mathrm{mA} \) )
- A. 20
- B. 35
- C. 10
- D. 40
Step-by-step solution
Using R = R₀[1 + α(T - T₀)], we find R at 120°C = 10 Ω [1 + (5×10⁻³)(100)] = 15 Ω. Since V is constant, I₂ = (I₁R₁)/R₂ = (30 mA × 10 Ω)/15 Ω = 20 mA.
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