In the following circuit, the reading of the ammeter will be (Take Zener breakdown voltage = 4 V) [figure]
- 60 mA
- 80 mA
- 10 mA
- 24 mA
Answer
(3) 10 mA
Solution
The Zener diode's cathode is connected to the positive terminal side of the 12 V source, so it is reverse biased.
∵ The voltage available (12 V) is more than the breakdown voltage, the Zener conducts and holds the voltage across it at 4 V.
The 400 resistor (with the ammeter) is in parallel with the Zener:
V400 = 4 V
⇒ I = 4400 A = 0.01 A = 10 mA
(Check: current through 100 = 12 - 4100 = 80 mA > 10 mA, so the Zener carries 70 mA and stays in breakdown.)
Answer: (3)