If the ratio of the concentration of electrons to that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4, then what is the ratio of their drift velocities? (a) 5/8 (b) 4/5 (c) 5/4 (d) 4/7

Answer: (c). I = neAvd ⇒ vd ∝ I/n for the same sample. (ve)/(vh) = (Ie)/(Ih) × (nh)/(ne) = 7/4 × 5/7 = 5/4 So the answer is (c) 5/4.

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Intrinsic & Extrinsic Semiconductors

If the ratio of the concentration of electrons to that of holes in a semiconductor is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4},$ then what is the ratio of their drift velocities?

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Answer: (c)

$I = neAv_d \Rightarrow v_d \propto \dfrac{I}{n}$ for the same sample.
$\dfrac{v_e}{v_h} = \dfrac{I_e}{I_h} \times \dfrac{n_h}{n_e} = \dfrac{7}{4} \times \dfrac{5}{7} = \dfrac{5}{4}$
So the answer is (c) $\dfrac{5}{4}$ .

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