Page 103 - Physics - XII

Q15. What constitutes the reverse current?
Ans. It is due to the minority charge carriers.

Q16. What is the order of magnitude of forward and reverse current?
Ans. Forward current is in milliampere while reverse current is in microampere.
Q17. Defi ne knee voltage.
Ans. The forward voltage beyond which the current starts to increase rapidly is called knee voltage.

Q18. How can you operate diode as a switch or as a rectifi er? (NCERT)
Ans. A diode can be used as a switch in certain circuits due to its unidirectional conduction property.
When a diode is forward-biased (positive voltage applied to the anode and negative to the cathode),
it allows current to fl ow easily, behaving like a closed switch. However, when the diode is reverse-
biased (negative voltage applied to the anode and positive to the cathode), it blocks the fl ow of
current, eff ectively acting as an open switch.

Q19. What is the diff erence between a diode and a resistor?
Ans. A diode is a type of electrical device that allows the current to move through it in only one direction.
A resistor is an electric component that is used to provide resistance to current in the circuit.

Q20. If a resistor of higher value (greater than the resistor connected in the circuit) is connected in
series with diode, then comment on the slope of linear region of I-V characteristics. (NCERT)
Ans. There will be no change in the slope of the linear region of the I-V characteristics.

Q21. What do you mean by doping?
Ans. The process of adding an impurity deliberately to the pure semiconductor is called doping.

Q22. How is p-n junction formed?
Ans. On heating a small pellet of indium placed on a piece of n-type Ge, some of the Indium melts and

penetrates into the n-type Ge, and p-n junction is formed.
Q23. What is a depletion layer?
Ans. A region near the p-n junction depleted of electrons and holes is termed as a depletion layer.

Q24. What do you mean by the term potential barrier?
Ans. Diff usion of electrons from n-region and holes from p-region towards the p-n junction gives rise to
the formation of barrier which opposes further diff usion, and is called potential barrier.

COMPETENCY BASED QUESTIONS

Multiple Choice Questions

Q1. In an unbiased p-n junction, holes diff use from the p-region to n-region because

(a) free electrons in the n-region attract them.
(b) they move across the junction by the potential diff erence.

(c) hole concentration in p-region is more as compared to n-region.
(d) all of these

101