Ncert Exercises & Solutions

Consider a box with three terminals on top of it as shown in figure.

Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement.

A student performs an experiment in which any two of these three terminals are connected in the circuit shown in figure.

The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit. The graphs are,

(i) when A is positive and B is negative

(ii) when A is negative and B is positive

(iii) when B is negative and C is positive

(iv) when B is positive and C is negative

(v) when A is positive and C is negative

(vi) when A is negative and C is positive

From these graphs of current-voltage characteristic shown in fig. (c) to (h), determine the arrangement of components between A, B and C.

Hint: The arrangement of A, B and C depends on the characteristics of the p-n junctions.

Step 1: Identify the arrangement in each case.

(a) In V-I graph of condition (i), a reverse characteristic is shown in fig. (c). Here A is connected to n-side of p-n junction I and B is connected to p-side of p-n junction I with a resistance in series.

(b) In V-I graph of condition (ii), a forward characteristic is shown in fig. (d), where 0.7 V is the knee voltage of p-n junction I, 1/slope=(1/1000)

Ω

It means A is connected to n-side of p-n junction I and B is connected to p-side of p-n junction I and resistance R is in series of p-n junction I between A and B.

(c) In V-I graph of condition (iii), a forward characteristic is shown in figure (e), where 0.7 V is the knee voltage. In this case p-side of p-n junction II is connected to C and n-side of p-n junction II to B.

(d) In V-I graphs of conditions (iv), (v), (vi) also concludes the above connection of p-n junctions I and II along with a resistance R.

Step 2: Draw the arrangement.

Thus, the arrangement of p-n I, p-n II and resistance R between A, B and C will be as shown in the figure.

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