Question

The ratio of concentration of electrons and holes in a semi-conductor is (7/5) and the ratio of currents is (7/4), then what is the ratio of their drift velocities? 

(A) (4/5) 

(B) (5/6) 

(C) (4/5) 

(D) (5/4)

Answer 1

The correct option is (D) (5/4).

Explanation:

(n₁ / n₂) = {(concentration of e) / (concentration of hole)}

= (7/5) and (I₁ / I₂) = (7/4)

 we know I = ne AV where V is drift velocity.

∴ I₁  = n₁ e AV₁

I₂ = n₂ e AV₂

∴ (I₁ / I₂) = (n₁ / n₂) (V₁ / V₂)

 ∴ (7/4) = (7/5) (V₁ / V₂)

∴ (V₁ / V₂) = (5/4)