The time required for a current to attain the maximum value in a d.c circuit containing L and R depends upon :

Options

A. R only
B. L only
C. L/R
D. none of these

Answer

To solve the question regarding the time required for a current to attain its maximum value in a DC circuit containing an inductor (L) and a resistor (R), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Circuit**:
- In a DC circuit with an inductor (L) and a resistor (R), when the circuit is closed, the current does not instantly reach its maximum value. Instead, it gradually increases.

2. **Current Equation**:
- The current (I) in an LR circuit can be expressed as:
\[ I(t) = I_{\text{max}} \left(1 - e^{-\frac{R}{L}t}\right) \]
- Here, \(I_{\text{max}}\) is the maximum current, \(R\) is the resistance, \(L\) is the inductance, and \(t\) is the time.

3. **Finding Maximum Current**:
- As time \(t\) approaches infinity, the exponential term \(e^{-\frac{R}{L}t}\) approaches zero. Thus, the current approaches its maximum value:
\[ I(t) \to I_{\text{max}} \quad \text{as} \quad t \to \infty \]

4. **Time to Reach Maximum Current**:
- Theoretically, the current never actually reaches \(I_{\text{max}}\) in a finite amount of time. It asymptotically approaches \(I_{\text{max}}\) as \(t\) becomes very large.

5. **Conclusion**:
- Therefore, the time required for the current to attain its maximum value in a DC circuit containing L and R is theoretically infinite.

### Final Answer:
The time required for the current to attain the maximum value in a DC circuit containing an inductor (L) and a resistor (R) is infinite. Hence, the correct option is **(d) none of these**.