# Hall Effect

1. Sep 10, 2007

### tigigi

Could anyone gives me some hints of how to solve these problems ?

1. a sample of Ge has both electrons and holes carrying the current. When a hall measurement is done, there's no hall effect. If the mobility of electrons in Germanium is 3500 cm^2/V.s and that of holes is 1500 cm^2/V.s, show that 30% of the current is carried the electrons.

2. a well lagged wire (no heat enters or leaves except at the ends) length L and cross sectional area A has its ends maintained at T1 and T2. The thermal conductivity of the wire K=B+CT where B and C are constants. Show that the rate of flow of heat along the wire is given by dQ/dt = A/L(T1-T2) {B+C/2 (T1+T2)}

Thank you. I appreciate it.

2. Sep 10, 2007

### Staff: Mentor

For 1, can one convert mobility into current.

Incidentally 1500/(1500 + 3500) = 0.3 or 30%, but 3500 cm^2/V.s is the mobility of electrons and 1500 cm^2/V.s the mobility of holes, so the electrons move much more readily.

for 2, think about Fourier's law in one dimension.

dQ/dt = - k A dT/dx

and remember k = k(T)