Unit of emf is

Options

A. `"joule"//"ampere"`
B. `"volt"//"ampere"`
C. `("henry-ampere")/("second")`
D. `"joule"//"coulomb"`

Explanation

To find the unit of electromotive force (emf), we can start by recalling the relationship between emf and other physical quantities.

### Step-by-Step Solution:

1. **Understand the Definition of EMF**:
Electromotive force (emf) is defined as the energy provided per unit charge by a source of electrical energy.

2. **Use the Formula**:
The formula that relates emf (E) to inductance (L) and the rate of change of current (di/dt) is given by:
\[ E = L \frac{di}{dt} \]

3. **Identify the Units**:
- The unit of inductance (L) is Henry (H).
- The unit of current (I) is Ampere (A).
- The unit of time (t) is second (s).

4. **Substituting Units into the Formula**:
Now, substituting the units into the formula:
\[ \text{Unit of } E = \text{Unit of } L \times \text{Unit of } \left(\frac{di}{dt}\right) \]
This gives us:
\[ \text{Unit of } E = \text{Henry} \times \left(\frac{\text{Ampere}}{\text{Second}}\right) \]

5. **Simplifying the Units**:
Therefore, we can express the unit of emf as:
\[ \text{Unit of } E = \text{Henry} \cdot \frac{\text{Ampere}}{\text{Second}} = \text{Henry Ampere per Second} \]

6. **Conclusion**:
Thus, the unit of electromotive force (emf) is Henry Ampere per Second.

### Final Answer:
The unit of emf is **Henry Ampere per Second**.

---