# Electronic Devices and Circuits Questions and Answers – BJT Circuits at DC

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This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “BJT Circuits at DC”.

1. Which of the following condition is true for cut-off mode?
a) The collector current Is zero
b) The collector current is proportional to the base current
c) The base current is non zero
d) All of the mentioned

Explanation: The base current as well as the collector current are zero in cut-off mode.

2. Which of the following is true for the cut-off region in an npn transistor?
a) Potential difference between the emitter and the base is smaller than 0.5V
b) Potential difference between the emitter and the base is smaller than 0.4V
c) The collector current increases with the increase in the base current
d) The collector current is always zero and the base current is always non zero

Explanation: Both collector and emitter current are zero in cut-off region.

3. Which of the following is true for a typical active region of an npn transistor?
a) The potential difference between the emitter and the collector is less than 0.5 V
b) The potential difference between the emitter and the collector is less than 0.4 V
c) The potential difference between the emitter and the collector is less than 0.3 V
d) The potential difference between the emitter and the collector is less than 0.2 V

Explanation: Most commonly used transistors have Vce less than 0.4 V for the active region.
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4. Which of the following is true for the active region of an npn transistor?
a) The collector current is directly proportional to the base current
b) The potential difference between the emitter and the collector is less than 0.4 V
c) All of the mentioned
d) None of the mentioned

Explanation: The base current and the collector current are directly proportional to each other and the potential difference between the collector and the base is always less than 0.4 V.

5. Which of the following is true for the saturation region of BJT transistor?
a) The collector current is inversely proportional to the base current
b) The collector current is proportional to the square root of the collector current
c) The natural logarithm of the collector current is directly proportional to the base current
d) None of the mentioned

Explanation: The collector current is directly proportional to the base current in the saturation region of the BJT.

6. Which of the following is true for a npn transistor in the saturation region?
a) The potential difference between the collector and the base is approximately 0.2V
b) The potential difference between the collector and the base is approximately 0.3V
c) The potential difference between the collector and the base is approximately 0.4V
d) The potential difference between the collector and the base is approximately 0.5V

Explanation: The commonly used npn transistors have a potential difference of around 0.5V between he collector and the base.

7. The potential difference between the base and the collector Vcb in a pnp transistor in saturation region is ________
a) -0.2 V
b) -0.5V
c) 0.2 V
d) 0.5 V

Explanation: The value of Vcb is -0.5V for a pnp transistor and 0.5V for an npn transistor.

8. For a pnp transistor in the active region the value of Vce (potential difference between the collector and the base) is
a) Less than 0.3V
b) Less than 3V
c) Greater than 0.3V
d) Greater than 3V

Explanation: For a pnp transistor Vce is less than 0.3V, for an npn transistor it is greater than 0.3V.

9. Which of the following is true for a pnp transistor in active region?
a) CB junction is reversed bias and the EB junction is forward bias
b) CB junction is forward bias and the EB junction is forward bias
c) CB junction is forward bias and the EB junction is reverse bias
d) CB junction is reversed bias and the EB junction is reverse bias

Explanation: Whether the transistor in npn or pnp, for it be in active region the EB junction must be reversed bias the CB junction must be forward bias.

10. Which of the following is true for a pnp transistor in saturation region?
a) CB junction is reversed bias and the EB junction is forward bias
b) CB junction is forward bias and the EB junction is forward bias
c) CB junction is forward bias and the EB junction is reverse bias
d) CB junction is reversed bias and the EB junction is reverse bias

Explanation: Whether the transistor in npn or pnp, for it be in saturation region the EB junction must be forward bias the CB junction must be forward bias.

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