Consider a p-n junction diode which has a potential drop of 0.5 V which is to be taken independent of current (under forward bias). If we want to use 1.5 V cell to forward bias the diode then what should be the value of resistor (in `Omega`) used in series with the diode so that current may not exceed 10 mA, and hence may work safely.

Answer

To solve this problem, we need to determine the value of the resistor that should be used in series with a p-n junction diode to ensure that the current does not exceed 10 mA when a 1.5 V cell is used to forward bias the diode.

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Voltage of the cell (V_cell) = 1.5 V
- Voltage drop across the diode (V_diode) = 0.5 V
- Maximum current (I_max) = 10 mA = 0.01 A

2. **Calculate the Voltage Across the Resistor:**
The voltage across the resistor (V_R) can be calculated using the formula:
\[ V_R = V_{cell} - V_{diode} \]
Substituting the values:
\[ V_R = 1.5 V - 0.5 V = 1.0 V \]

3. **Use Ohm's Law to Find the Resistance:**
According to Ohm's Law, the resistance (R) can be calculated using the formula:
\[ R = \frac{V_R}{I} \]
Substituting the values for V_R and I_max:
\[ R = \frac{1.0 V}{0.01 A} = 100 \, \Omega \]

4. **Conclusion:**
The value of the resistor that should be used in series with the diode to ensure that the current does not exceed 10 mA is **100 Ω**.