Electronic Devices and Circuits Questions and Answers – The CB Characteristics

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

1. The input resistance in a CB transistor is given by _________
a) ∆VCE/∆IB
b) ∆VBE/∆IB
c) ∆VBE/∆IC
d) ∆VEB/∆IE

Explanation: The ratio of change in emitter base voltage (∆VEB) to resulting change in emitter current (∆IE) at constant collector base voltage (VCB) is defined as input resistance. This is denoted by ri.

2. The output resistance of CB transistor is given by _________
a) ∆VCB/∆IC
b) ∆VBE/∆IB
c) ∆VBE/∆IC
d) ∆VEB/∆IE

Explanation: The ratio of change in collector base voltage (∆VCB) to resulting change in collector current (∆IC) at constant emitter current (IE)¬ is defined as output resistance. This is denoted by ro.

3. Which one of the following depicts the output characteristics for a CB transistor?
a)
b)
c)
d)

Explanation: A graph of IC against VCB is drawn. The curve so obtained is known as output characteristics. The emitter current (IE) is kept constant.

4. The input characteristics of a CE transistor is_________
a)
b)
c)
d)

Explanation: A graph of IE against VEB is drawn. The curve so obtained is known as input characteristics. The collector base voltage (VBC) is kept constant.

5. A transistor is connected in CB configuration. The emitter voltage is changed by 200mV, the emitter by 5mA. During this transition the collector base voltage is kept constant. What is the input dynamic resistance?
a) 30Ω
b) 60Ω
c) 40Ω
d) 50Ω

Explanation: The ratio of change in emitter base voltage (∆VEB) to resulting change in emitter current (∆IE) at constant collector base voltage (VCB) is defined as input resistance. This is denoted by ri.
We know, ∆VEB/∆IE=ri
=200/5=40Ω.
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6. When the collector junction is reverse biased and emitter junction is forward biased, the operating region of the transistor is called_________
a) inverted region
b) active region
c) cut off region
d) cut in region

Explanation: In the active region, for small values of base current, the effect of collector voltage over collector current is small while for large base currents this effect increases. The shape of characteristic here is same as that of CB transistors.

7. Which of the following corresponds to the output circuit of a CB transistor?
a) VBE
b) IB
c) VCB
d) VCE

Explanation: Here, the quantity collector to base voltage corresponds to the output circuit of a CB transistor. The complete electrical behaviour of a transistor can be described by stating the relation between these quantities.

8. The input of a CB transistor is given between_________
a) collector and emitter terminals
c) ground and emitter terminals
d) emitter and base terminals

Explanation: The name of the CB transistor says that it’s a common based one. The input is given between the emitter and base terminals and the output is taken between collector and base terminals.

9. The current gain of the CB transistor is_________
a) less than or equal to unity
b) equal to unity
c) greater than unity
d) remains same

Explanation: The input current flowing into the emitter terminal must be higher than the base current and collector current to operate the transistor. Therefore the output collector current is less than the input emitter current.

10. The input characteristics of a CB transistor resembles_________
a) Forward biased diode
b) Illuminated photo diode
c) LED
d) Zener diode

Explanation: The input characteristics resemble the illuminated photo diode and the output characteristics resemble the forward biased diode. This transistor has low input impedance and high output impedance.

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

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