Question

Which of the PN junctions is forward biased?

Answer 1

For solving this question, first we need to know the difference between forward bias and reverse bias. In forward biased PN junction, p-type is connected to positive terminal with higher voltage; whereas in reversed biased PN junction, p-type is connected to negative terminal with lower voltage compared to the terminal connected with n- type.

Complete step by step answer:
In this problem, we are asked to find a PN junction which is forward biased.

As shown in diagram, the PN junction is called forward biased if p-type is connected with higher voltage than n-type which is connected with lower voltage. And if p-type is connected with lower voltage than n-type which is connected with higher voltage, then it is called
reversed biased.Now, if we take into consideration the given options, it is clearly observed that the PN junction given in option C is forward biased because in that p-type is connected with $0V$ and n-type is connected with $- 2V.$ As p-type is connected to higher voltage than n-type it is a forward biased PN junction.

Hence, option C is the right answer.

Note: If we consider other options, then
In option A, p-type is connected to $10V$ and n=type is connected with $20V$.Clearly, $10V$ is less than $20V$, therefore, this PN junction is reversed biased.Similarly, in option B, p-type is connected to $- 10V$ and n=type is connected with $- 5V$.Clearly, $- 10V$ is less than $- 5V$, therefore, this PN junction is reversed biased.Thus, we can say that whether the PN junction is forward or reversed biased is dependent on the voltage value with which the p-type and n-type are connected relatively.