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 positve

(iv) When B is positive and C is neagtive

(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.

Explanation

(a) In `V - I` graph of condition (i), a reverse characteristics 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 characteristics is shown in fig. (d), where `0.7 V` is the knee voltage of `p - n` junction `11//`slope `= (1//1000) Omega`.
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 characteristics is shown in figure (e), where `0.7V` 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` junction `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.