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In a semiconductor, the ratio of electron current to hole current is 7/4, and the ratio of the drift velocity of electrons to that of holes is 5/4. What is the ratio of the electron concentration to the hole concentration?

1. 5/7
2. 7/5
3. 25/49
4. 49/25

Correct answer: 7/5

Solution

Current I = n*e*vd*A, so Ie/Ih = (ne/nh)*(vde/vdh). Thus 7/4 = (ne/nh)*(5/4), giving ne/nh = 7/5.

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