Question:

The forward resistance for silicon diode carrying a current of \(20~mA\) is

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For silicon diodes, \[ V_F \approx 0.7V \] and for germanium diodes, \[ V_F \approx 0.3V. \] These values are frequently used in numerical problems.
Updated On: Jun 25, 2026
  • \(15~\Omega\)
  • \(35~\Omega\)
  • \(50~\Omega\)
  • \(20~k\Omega\)
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The Correct Option is B

Solution and Explanation

Concept: The DC forward resistance of a diode is defined as \[ R_f=\frac{V_F}{I_F} \] where \[ V_F=\text{forward voltage} \] and \[ I_F=\text{forward current}. \] For a silicon diode, \[ V_F \approx 0.7V. \]

Step 1:
Write the given values.
\[ V_F=0.7V \] \[ I_F=20mA=0.02A \]

Step 2:
Apply the forward resistance formula.
\[ R_f = \frac{V_F}{I_F} \] \[ = \frac{0.7}{0.02} \] \[ = 35\Omega \]

Step 3:
State the result.
Therefore, \[ \boxed{R_f=35\Omega} \]
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