Question: Q. 1. (i) Explain with the help of a diagram, how a depletion layer and barrier potential are formed in a junction diode.
[Delhi & Delhi Comptt. I, II, III 2014] (ii) Draw a circuit diagram of full-wave rectifier. Explain its working and draw input and output waveforms.
U] [Delhi Comptt. I, II, III 2014; O.D. I, II, III 2013; Delhi I, II, III 2012; O.D. I, II, III, 2011]
Due to the diffusion of electrons and holes, from their majority zone to minority zone, a layer of positive and negative space charge region on either side on the junction is formed. This is called the depletion region.
The loss of electrons, from n-region and the gain of electrons by the $p$-region, cause a difference of potential across the junction. This tends to prevent the movement of charge carriers across the junction and is, therefore, termed as barrier potential.
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(ii) Try yourself, Similar to Q. 1 (ii), Short Answer Type Question-II.
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[CBSE Marking Scheme, 2014, 13, 12, 11]
Q. 2. (i) Draw the circuit arrangement for studying the $I-V$ characteristics of a $p-n$ junction diode in (a) forward and (b) reverse bias. Briefly explain how the typical $I-V$ characteristics of a diod are obtained and draw these characteristics.
[Delhi I, II, III, O.D. Comptt. I, II, UI 2014]
(ii) With the help of necessary circuit diagram explain the working of a photodiode used for detecting optical signals.
U] [O.D. Compt. 1, II, III 2014, 2013]
Show Answer
Solution:
Ans. (i) Forward biasing
Reverse biasing
Biasing
The $V$-I characteristics are obtained by connecting the battery, to the diode, through a potentiometer (or rheostat). The applied voltage to the diode is changed. The values of current, for different values of voltage, are noted and a graph between $V$ and $I$ is plotted. The $V-I$ characteristics of a diode, have the form shown here.
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$1 / 2+1 / 2$
(ii) Try yourself Similar to Q. 12, Short Answer Type Questions-II)
[CBSE Marking Scheme 2014, 13]
