JEE Main 2022 · 28 June · morning · Single correct · +4 / −1
Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : n-p-n transistor permits more current than a p-n-p transistor.
Reason R : Electrons have greater mobility as a charge carrier.
Choose the correct answer from the options given below :
- (a) Both A and R are true, and R is correct explanation of A.
- (b) Both A and R are true but R is NOT the correct explanation of A.
- (c) A is true but R is false.
- (d) A is false but R is true.
Answer and solution
Answer (a) Both A and R are true, and R is correct explanation of A.
Solution
Physics sir · 4 steps
Ask who carries the current: in n-p-n it is electrons, and electrons move faster than holes.
- Main carriers. In an n-p-n transistor the emitter is n-type, so electrons carry most of the current. In a p-n-p transistor the emitter is p-type, so holes carry it.
- Check R. Electrons move freely in the conduction band. Holes move only when bound electrons hop from one bond to the next, which is slower. So in silicon, electron mobility is about 3 times hole mobility. R is true.
- Check A. Current depends on how fast the carriers drift: I = neAv_d and v_d = μ E. With higher mobility, an n-p-n transistor gives more current under the same conditions. A is true.
- So. A is true because of R: the larger current comes straight from the higher mobility of electrons. The answer is (a).
The idea to keep. To compare n-p-n with p-n-p, first ask which carrier does the work. Electrons have higher mobility than holes, so n-p-n devices are faster and carry more current.
Answer from the NTA final answer key. Solution by PrepWiser.