The first junction on transistor consisting of two back to back P-N junction was invented in 1951 by William Shockley. Later new Bipolar Junction Transistor (BJT) were invented. Transistor has three doped regions forming two P-N junction between them. There are two types of transistors (i) P-N-P and (ii) N-P-N. Each transistor has three segments (i) Emitter (ii) Base (iii) Collector. The size and level of doping is different of all three segments. For connecting in the circuit three terminals of a transistor are available - emitter, base and collector and it can be connected in three configuration Common Emitter (CE), Common Base (CB) and Common Collector (CC). The transistor can be used as a device application depending on configuration used, the biasing done to the segments and operate in the region namely cut off, Active and Saturation. It can work as an amplifier, a switch and an oscillator too. Based on transistor knowledge give answer.
Match List 1 with List 2
| List 1 | List 2 |
| (A) Transistor used as an amplifier | (I) Output signal is a self sustained AC signal |
| (B) Transistor used as a switch | (II) Base current \( I_B \) is an input current with \( V_{CE} \) as an output voltage |
| (C) Transistor used as an oscillator | (III) Transistor works only in Active region |
| (D) Transistor in CE configuration | (IV) Transistor does not exist in active region |
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-(III), B-(IV), C-(I), D-(II)
The use of a transistor depends on the region of operation.
(A) Transistor used as an amplifier — this matches (III) Transistor works only in Active region. Amplification needs the output to follow the input linearly, which happens only in the active region.
(B) Transistor used as a switch — this matches (IV) Transistor does not exist in active region. As a switch it is driven between cut-off (OFF) and saturation (ON) and is not left in the active region.
(C) Transistor used as an oscillator — this matches (I) Output signal is a self sustained AC signal. An oscillator uses positive feedback to produce an AC output without any external input signal.
(D) Transistor in CE configuration — this matches (II) Base current \( I_B \) is an input current with \( V_{CE} \) as an output voltage. The input is the base current \( I_B \) and the output is taken between collector and emitter.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Transistor as a Device – “… When the transistor is used in the cutoff or saturation state it acts as a switch. On the other hand for using the transistor as an amplifier, it has to operate in the active region.”