Which of the following circuits is reverse - biased?

Solution

Physics sir · 3 steps

Do not judge by the signs alone: compare the anode's potential with the cathode's in every circuit.

1. Read the symbol. In the diode symbol the triangle side is the p-side (anode) and the bar is the n-side (cathode). A resistor in series does not change which side is at the higher potential.
2. The bias rule. If the anode is at a higher potential than the cathode, the diode is forward biased. If the cathode is higher, it is reverse biased.

   Circuit	Anode (p-side)	Cathode (n-side)	Bias
   (a)	+2 V	-10 V (via R)	forward
   (b)	0 V (ground)	-5 V (via R)	forward
   (c)	+2 V (via R)	0 V (ground)	forward
   (d)	+2 V	+4 V (via R)	reverse

3. So. Only in (d) is the n-side at a higher potential (+4 V) than the p-side (+2 V), so circuit (d) is reverse biased.

The idea to keep. Bias depends only on which side is at the higher potential. A negative number or a positive number on its own tells you nothing. Compare the p-side with the n-side every time.

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