# Electronic Devices and Circuits Questions and Answers – The Unijunction Transistors

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Unijunction Transistors”.

1. How many terminals are there in a unijunction transistor?
a) 1
b) 2
c) 3
d) 4

Explanation: A unijunction transistor consists of three terminals. It is a semiconductor device that displays negative resistance and switching characteristics. It is used as a relaxation oscillator in phase control applications.

2. What are unijunction transistors used for?
a) Amplifying a circuit
b) Circuit breaker
c) Splitting device
d) On-Off switching device

Explanation: Unlike bipolar transistors or field effect transistors these unijunction transistors cannot be used to amplify a circuit. The unijunction transistors are used as an on-off switching transistor. They have unidirectional conductivity.

3. Unijunction transistors have unidirectional conductivity and positive impedance characteristics.
a) True
b) False

Explanation: Unijunction transistors have unidirectional conductivity and negative impedance characteristics. During circuit breakdown, they function more as a variable voltage divider. They are used in gate pulse, timing circuits and trigger generation.

4. What is the generalized value for the voltage across resistor RB1 in a unijunction transistor?
a) VRB1 = (RB2 / RB1 + RB2) × VBB
b) VRB1 = (RB2 / RB1 – RB2) × VBB
c) VRB1 = (RB1 / RB1 + RB2) × VBB
d) VRB1 = (RB1 / RB1 – RB2) × VBB

Explanation: The generalized value for the voltage across resistor RB1 is (RB1 / RB1 + RB2) × VBB. Where, RB1 and RB2 are the resistance across two terminals B1 and B2. The voltage VBB is the voltage across the two terminals.

5. What is the intrinsic stand-off ratio(η) of a unijunction transistor when RB1 = 10kΩ and RBB = 15kΩ?
a) 0.67
b) 0.55
c) 0.80
d) 0.44

Explanation: The intrinsic stand-off ratio(η) is equal to the ratio RB1 / RBB. Standard values of η range from 0.5 to 0.8. Given RB1 = 10kΩ and RBB = 15kΩ:
η = RB1 / RBB = 10 / 15 = 0.67
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6. Which type of material is the channel of a unijunction transistor made up of?
a) PN type
b) It doesn’t affect the working
c) P type
d) N type

Explanation: The core conducting component is the N-type channel of the transistor. Unijunction transistor consists of a single solid piece of N-type semiconductor material forming the main current carrying channel.

7. What are the terminals of a unijunction transistor?
a) Collector, Base and Emitter
b) Emitter, Base 1 and Base 2
c) Gate, Drain and Source
d) Gate, Drain, Body and Source

Explanation: The unijunction transistor consists of a single solid piece of N-type channel with its two outer connections marked as Base 2 and Base 1. The third connection is the Emitter and it is located along the channel. The emitter lies closer to base 2 as compared to base 1.

8. What are the working regions of a unijunction transistor?
a) Linear region
b) Negative Resistance region
c) Saturation region
d) Cut-off region

Explanation: As soon as the transistor reaches the triggering voltage the unijunction transistor will turn on. If the applied voltage increases to the emitter lead, the peak voltage is achieved. The voltage drops from peak voltage to Valley Point. This happens in spite of the current increasing; this is because of the negative resistance.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.