A constant current of `2.8 A` exists in a resistor. The rms current is

Options

A. `2.8 A`
B. about `20 A`
C. `1.4 A`
D. undefined for a direct current

Answer

To find the RMS (Root Mean Square) current when a constant current is given, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of RMS Current**:
- The RMS current is a measure of the effective current that delivers the same power to a resistor as a direct current (DC) of the same value.

2. **Identify the Given Information**:
- We are given a constant current of `2.8 A`.

3. **Apply the Definition of RMS Current**:
- For a constant current, the RMS value is equal to the value of the current itself. This is because the RMS value is calculated using the formula:
\[ I_{RMS} = \sqrt{\frac{1}{T} \int_0^T I(t)^2 dt} \]
For a constant current \( I \), this simplifies to:
\[ I_{RMS} = I \]

4. **Calculate the RMS Current**:
- Since the current is constant at `2.8 A`, we can directly state:
\[ I_{RMS} = 2.8 A \]

5. **Conclusion**:
- Therefore, the RMS current is `2.8 A`.

### Final Answer:
The RMS current is **2.8 A**.

---