Question

Consider a box with three terminals on top of it as shown in figure (a):

(a)

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 (b).

(b)

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

(c)

(ii) when A is negative and B is positive

(d)

(iii) When B is negative and C is positive

(e)

(iv) When B is positive and C is negative

(f)

(v) When A is positive and C is negative

(g)

(vi) When A is negative and C is positive

(h)

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

Answer 1

The V-I characteristics of these graphs are discussed in points:

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

(b) In the V-I graph of condition (ii), a forward characteristic is shown in figure (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 the n-side of p-n junction I and B is connected to the p-side of p-n junction I and resistance R is in a series of p-n junction I between A and B.

(c) In the 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 the 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.

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.