Question

In the following circuit, the reading of the ammeter will be: (Take Zener breakdown voltage = 4 V)

• A. 24 mA
• B. 80 mA
• C. 10 mA
• D. 60 mA

Hint:

When dealing with Zener diodes in circuits, the voltage across the diode remains constant at the breakdown voltage. Use Ohm's law to find the current through the rest of the circuit.

Answer 1

The Correct Option is C

Given:

• Supply voltage \( V_s = 12 \, \text{V} \)
• Series resistor \( R_s = 100 \, \Omega \)
• Zener breakdown voltage \( V_Z = 4 \, \text{V} \)
• Load resistor \( R_L = 400 \, \Omega \)

Step 1: Zener Diode Operation
The supply voltage (\( V_s = 12 \, \text{V} \)) exceeds the Zener breakdown voltage (\( 4 \, \text{V} \)). Consequently, the Zener diode operates in its breakdown region, maintaining a stable \( 4 \, \text{V} \) across itself.
Step 2: Voltage Across Load Resistor
The Zener diode and load resistor are connected in parallel. Thus, the voltage across the load resistor equals the Zener voltage: \[ V_{R_L} = V_Z = 4 \, \text{V} \] 
Step 3: Current Through Load Resistor (Measured by Ammeter)
The current through the load resistor is calculated using Ohm's Law: \[ I = \frac{V}{R} = \frac{4}{400} = 0.01 \, \text{A} = 10 \, \text{mA} \] 
Step 4: Ammeter Reading
The ammeter is placed in series with the \( 400 \, \Omega \) load resistor, directly measuring the current flowing through it. 
Therefore, the ammeter reading is: \[ 10 \, \text{mA} \]