The I-V characteristics of an electronic device shown in the figure. The device is :

Solution

Physics sir · 4 steps

Look at the left end of the graph: that sharp vertical drop in reverse bias is the zener breakdown.

1. Forward bias. On the right of the origin the current rises slowly, then faster. This is the usual p-n junction forward characteristic.
2. Reverse bias. On the left only a tiny current flows, of the order of μA, until one particular reverse voltage. There the current shoots up almost vertically.
3. Why it regulates. On that vertical part the current can change a lot while the voltage stays almost fixed. A device that holds its voltage constant while the current varies is a voltage regulator. This is exactly how a zener diode is used, in reverse bias.

   Device	What its graph looks like	Matches?
   Solar cell	Curve shifted into the fourth quadrant; current is not zero at V = 0	No, this curve passes through the origin
   Transistor	A family of output curves, one for each base current	No, there is only one curve here
   Rectifier diode	Forward conduction, small reverse current; never meant to work in breakdown	No, the graph is built around the breakdown
   Zener diode	Forward conduction plus a sharp, vertical reverse breakdown	Yes

4. So. The device is a zener diode used as a voltage regulator, option (d).

The idea to keep. A sharp, nearly vertical rise in reverse current at a fixed voltage means zener breakdown. Constant voltage over a wide range of current is what makes it a voltage regulator.

Answer from the NTA final answer key. Solution by PrepWiser.