Question

In the circuit shown in figure, if the diode forward voltage is $0.3\,V$ , the voltage difference between $A$ and $B$ is:

A) $1.3\,V$
B) $2.3\,V$
C) $0$
D) $0.5\,V$

Answer 1

Use the formula of the ohm’s law, find the potential difference across the circuit. From the obtained answer and the given forward diode voltage, calculate the total potential difference across the point $A$ and $B$ by using the below formula.

Useful formula:
(1) The potential difference between two points is given by
$V = v + {v_d}$
Where $V$ is the potential difference, $v$ is the potential across the circuit and ${v_d}$ is the diode voltage.
(2) The ohm’s law is given by
$v = IR$
Where $I$ is the current flowing through the circuit and $R$ is the resistance in the circuit.

Complete step by step solution:
From the diagram, the given data, ${v_d} = 0.3\,V$
The current flowing through the circuit, $I = 0.2\,mA$
The resistance in the circuit,
${R_1} = 5\,K\Omega \\\ {R_2} = 5\,K\Omega \\\$
The total resistance in the circuit is calculated by adding the resistance of the resistors present in the circuit.
$R = {R_1} + {R_2} = 5 + 5 = 10\,k\Omega$
By using the ohm’s law,
$v = IR$
Substituting the values in the above equation
$v = \left( {0.2 \times {{10}^{ - 3}}} \right) \times \left( {10 \times {{10}^3}} \right)$
$v = 0.0002 \times \left( {10000} \right)$
By performing the simple arithmetic operations,
$v = 2\,V$
The forward voltage from the circuit is obtained by subtracting the total voltage entering the circuit and the voltage that is used by the circuit. Using the formula (1) for calculating the potential difference
$V = v + {v_d}$
$V = 2 + 0.3$
By performing addition in the above step,
$V = 2.3\,V$
Hence the potential difference across the point $A$ and $B$ is $2.3\,V$.

Thus the option (B) is correct.

Note: The forward diode voltage is the amount of the voltage that is used by the diode to allow the current flow in it. When the forward voltage is positive, the diode is considered as on and the current flow through the diode. If not, the current does not flow.