Question

A pure germanium rod has a radius of 1cm and length 4cm. A p.d of 4V is applied across the ends of rod. The concentration of holes in the rod is 2.5 x 10¹⁹ m^-3. The mobility of electrons and holes is 0.36 m² V^-1 s^-1 and 0.18 m² V^-1 s^-1 respectively. The current in rod is

(1) 45.2 mA

(2) 22.6 mA

(3) 67.8 mA

(4) 56.3 mA

Answer 1

(3) 67.8 mA

The electric field in rod

Let v_e and v_h be the average drift speed accquired by electron and holes respectively under the applied electric field. Let μ_e and μ_n be mobility of electron and hole. Then

The current, I_e ; due to motion of electrons is