Question

A tungsten filament at 25-degree celsius has a resistance of 0.350 ohms. What would be the resistance if the temperature is increased to 2850°C? The temperature coefficient of resistance for tungsten is 0.5*10^-3 /°C

Answer 1

R₂₈₅₀ = 0.838 ohms

Step-by-step explanation:

The resistance of an element at some other temperature than 0°C can be given by the following formula:

Rₓ = R₀(1 + ∝ΔT)

where,

Rₓ = Resistance at temperature x

R₀ = Resistance at 0°C

∝ = Coefficient of linear expansion of tungsten = 0.5 x 10⁻³ /°C

ΔT = Change in Temperature

So, for the resistance of tungsten wire at 25°C:

Rₓ = R₂₅ = 0.35 ohms

ΔT = 25°C

Therefore,

0.35 ohms = R₀[1 + (0.5 x 10⁻³ /°C)(25°C)]

R₀ = (0.35 ohms)/1.0125

R₀ = 0.345 ohms

Now, we find the resistance at 2850°C

R₂₈₅₀ = (0.345 ohms)[1 + (0.5 x 10⁻³ /°C)(2850°C)]

R₂₈₅₀ = 0.838 ohms