Which is not a unit of electric field

Options

A. `NC^(-1)`
B. `Vm^(-1)`
C. `JC^(-1)`
D. `JC^(-1)m^(-1)`

Explanation

To determine which option is not a unit of electric field, we need to understand the units associated with electric fields and analyze the provided options.

### Step-by-Step Solution:

1. **Understanding Electric Field**: The electric field (E) is defined as the force (F) experienced by a unit charge (Q) placed in the field. The formula for electric field can be expressed as:
\[ E = \frac{F}{Q} \]

2. **Units of Force**: The unit of force (F) is Newton (N). The unit of charge (Q) is Coulomb (C). Therefore, the unit of electric field can be derived as:
\[ \text{Unit of Electric Field} = \frac{\text{Unit of Force}}{\text{Unit of Charge}} = \frac{\text{N}}{\text{C}} = \text{N C}^{-1} \]

3. **Alternative Expression**: The electric field can also be expressed in terms of voltage (V) and distance (d):
\[ E = \frac{V}{d} \]
The unit of voltage is Volt (V), and the unit of distance is meter (m). Thus, we can express the unit of electric field as:
\[ \text{Unit of Electric Field} = \frac{\text{V}}{\text{m}} = \text{V m}^{-1} \]

4. **Energy and Electric Field**: The potential energy (U) per unit charge is given in Joules per Coulomb (J/C), which can also be expressed in terms of electric field:
\[ \text{Unit of Electric Field} = \frac{\text{J}}{\text{C m}} = \text{J C}^{-1} \text{ m}^{-1} \]

5. **Identifying the Incorrect Unit**: Now, we need to analyze the options provided. The valid units of electric field include:
- Newton per Coulomb (N C^{-1})
- Volt per meter (V m^{-1})
- Joule per Coulomb per meter (J C^{-1} m^{-1})

If one of the options is "Joule per Coulomb" (J C^{-1}), this is not a unit of electric field but rather a unit of electric potential.

6. **Conclusion**: Based on the analysis, the option that is not a unit of electric field is "Joule per Coulomb" (J C^{-1}).

### Final Answer:
The option that is not a unit of electric field is **Joule per Coulomb (J C^{-1})**.