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MCQEasyJEE 2023Transistors (BJT: Amplifier & Switch)

JEE Physics 2023 Question with Solution

Given below are two statements:

Statement I: In a typical transistor, all three regions emitter, base, and collector have same doping level. Statement II: In a transistor, collector is the thickest and base is the thinnest segment. In light of the above statements, choose the most appropriate answer from the options given below.

  • A

    Both Statement I and Statement II are correct

  • B

    Both Statement I and Statement II are incorrect

  • C

    Statement I is incorrect but Statement II is correct

  • D

    Statement I is correct but Statement II is incorrect

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: Two statements about the structure of a typical transistor.

Find: Which statement is correct.

Statement I: The doping levels of emitter, base, and collector are not the same. The emitter is heavily doped, the base is lightly doped, and the collector is moderately doped. Therefore, Statement I is incorrect.

Statement II: The collector is the thickest region because it has to dissipate more heat, and the base is the thinnest region to enable effective transistor action. Therefore, Statement II is correct.

Thus, the correct answer is Statement I is incorrect but Statement II is correct. Hence, the correct option is C.

The solution labels the correct option as D, but the written explanation matches option C in the given options.

Statement-wise Analysis

Given: A statement-based question on transistor construction.

Find: The most appropriate option.

For a typical transistor:

  • Emitter is heavily doped so that it can inject a large number of charge carriers.
  • Base is lightly doped and very thin so that recombination is minimal.
  • Collector is moderately doped and made thicker to collect carriers and withstand more heat.

So, the three regions do not have the same doping level. Hence Statement I is false.

Also, the collector being the thickest and the base being the thinnest is correct. Hence Statement II is true.

Therefore, the correct option is C.

Common mistakes

  • Assuming all three transistor regions have the same doping because they are part of one semiconductor device is incorrect. Each region is doped differently to perform a specific function. Remember: emitter is heavily doped, base is lightly doped, and collector is moderately doped.

  • Confusing thickness with doping level is a common error. The base is made very thin for carrier transport, while the collector is thicker mainly for heat dissipation and collecting carriers. Do not treat geometric thickness and doping concentration as the same property.

  • Following the option letter shown on the solution without checking the written explanation can lead to a wrong answer. Here, the explanation clearly supports option C, so always match the statement conclusion with the actual listed options.

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