A potential divider circuit is connected with a dc source of 20 V, a light emitting diode of glow in voltage 1.8 V and a zener diode of breakdown voltage of 3.2 V. The length (PR) of the resistive wire is 20 cm. The minimum length of PQ to just glow the LED i $s ______$ cm.

Question

G1 Physics · Accepted Answer

Image For the LED to just glow, the required potential difference between P and Q is: V(PQ) = 1.8 + 3.2 = 5.0 V The entire resistive wire PR has 20 V across 20 cm. Therefore voltage is proportional to length: V(PQ)/V(PR) = PQ/PR 5/20 = PQ/20 Hence: PQ = 5 cm

A potential divider circuit is connected with a dc source of 20 V, a light emitting diode of glow in voltage 1.8 V and a zener diode of breakdown voltage of 3.2 V. The length (PR) of the resistive wire is 20 cm. The minimum length of PQ to just glow the LED i s ______ cm.