Question

12. The temperature coefficient of resistance of a
wire is 0.00125 per °C. At 20°C, its resistance
is 1 ohm The resistance of the wire will be 2 ohm at
(a) 800 °C
(b) 700 °C
(c) 850 °C
(d) 820 °C​

Answer 1

Answer :

Temp. coefficient = 0.00125 °C‾¹

Resistance at 20°C = 1Ω

We have to find that temperature when resistance will become 2Ω$.$

★ Resistance of conductor depends upon length of conductor, area of cross section and temperature.

Change in resistance of conductor is directly proportional to the change in temperature.

• ∆R ∝ ∆T

Putting proportionality constant, we get

• ∆R = R × α × ∆T

R denotes resistance at initial temperature

α denotes coefficient of temperature

By substituting the values,

➝ (R₂ - R₁) = R₁ × α × (T₂ - T₁)

➝ (2 - 1) = 1 × 0.00125 × (T - 20)

➝ T - 20 = 1/0.00125

➝ T = 800 + 20

➝ T = 820°C

∴ (D) is the correct answer.