JEE Main 2020 · 7 January · evening · Single correct · +4 / −1
In the figure, potential difference between A and B is :
- (a) 10 V
- (b) 5 V
- (c) zero
- (d) 15 V
Answer and solution
Answer (a) 10 V
Solution
Physics sir · 3 steps
First decide whether the diode conducts. Here it does, so the two 10 kΩ resistors share the current.
- Diode direction. The longer plate of the cell is on top, so the top wire is at the higher potential and current reaches A through the 10 kΩ resistor. The diode points from A to the right branch, so it is forward biased. Treat the ideal diode as a plain wire.
- Parallel pair. Between A and B there are now two 10 kΩ resistors in parallel. Together they give 5 kΩ. That 5 kΩ is in series with the first 10 kΩ.
V_(AB) = 30 V × (5 kΩ)/(10 kΩ + 5 kΩ) = 10 V
- So. The current is 30/15 kΩ = 2 mA. The drop across the 5 kΩ combination is 2 mA × 5 kΩ = 10 V, which is option (a).
The idea to keep. With a diode in a circuit, check its bias first. Forward biased (ideal) means a wire, and reverse biased means a break. Then it is an ordinary series-parallel potential divider.
Answer from the NTA final answer key. Solution by PrepWiser.