In the Zener-diode circuit shown in the original figure, the supply is 12 V, the series resistor is 100 Ω, the load branch contains 400 Ω and the Zener breakdown voltage is 4 V. The ammeter reading is:

Question

G1 Physics · Accepted Answer

First check whether the Zener conducts. Without Zener action, the voltage across the 400 Ω load would be V l o a d V_load V l ​ o a d = 12×400/(100+400) = 9.6 V. Since 9.6 V > 4 V, the Zener enters breakdown and clamps the load voltage to 4 V. Therefore the load current measured by the ammeter is I = V/R = 4/400 = 0.01 A = 10 mA. Correct option: C.