It is much easier to measure the electrical conductivity of a material than to measure its thermal conductivity. Use the Wiedemann-Franz law to find the thermal conductivities of (a) an alloy that has an electrical resistivity p_e of 28 mu ohm cm. (b) tungsten of the kind used for lamp filaments that has an electrical conductivity k_e of 9.9 times 10^6 S/m (as S/m is 1/ohm m).

The Wiedemann-Franz law states that the ratio of the electrical conductivity (k_e) to the thermal conductivity (k_th) of a material is proportional to the temperature (T).

This relationship can be expressed as:

k_e / k_th = L * T

where L is the Wiedemann-Franz constant, which is a universal constant that is approximately equal to 2.44 x 10^-8 W/K^2.

To find the thermal conductivity of a material using the Wiedemann-Franz law, we can rearrange the equation as follows:

k_th = k_e / (L * T)

To find the thermal conductivity of an alloy that has an electrical resistivity p_e of 28 mu ohm cm, we can use the following equation:

k_th = 1 / (p_e * L)

Substituting the values given, we get:

k_th = 1 / (28 mu ohm cm * 2.44 x 10^-8 W/K^2)

= 14.6 W/K

To find the thermal conductivity of tungsten of the kind used for lamp filaments that has an electrical conductivity k_e of 9.9 x 10^6 S/m, we can use the following equation:

k_th = k_e / (L * T)

Substituting the values given, we get:

k_th = 9.9 x 10^6 S/m / (2.44 x 10^-8 W/K^2)

= 402 W/K

So, the thermal conductivity of the alloy is 14.6 W/K and the thermal conductivity of tungsten is 402 W/K.

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