Question

In the following electrical circuit, the reading in the milliammeter is
(Take knee voltage of silicon diode \(= 0.7\) V)

• A. \(25.5\) mA
• B. \(21.5\) mA
• C. \(18.5\) mA
• D. \(15.8\) mA

Hint:

The diode is forward biased, so subtract the knee voltage from the battery voltage before applying Ohm's law.

Answer 1

The Correct Option is B

Step 1: Read the circuit
The figure shows a 5 V battery in series with a silicon diode, a \(200\ \Omega\) resistor and a milliammeter. The diode symbol points from the positive terminal side toward the resistor, so the diode is forward biased.

Step 2: Account for the diode
A forward-biased silicon diode conducts once the voltage across it reaches the knee voltage of \(0.7\) V, and then it drops about \(0.7\) V. So the voltage across the resistor is \(5 - 0.7 = 4.3\) V.

Step 3: Apply Ohm's law
\[ I = \frac{4.3}{200} = 0.0215\ \text{A} = 21.5\ \text{mA} \]

Step 4: Check
Option (B). The value 25 mA would be \(5/200\), which ignores the diode drop.

Final Answer:
The milliammeter reads 21.5 mA. This is option (B). \[ \boxed{\text{(B) }21.5\ \text{mA}} \]