The SI unit of electric field intensity is

Options

A. netweon/coulomb
B. joule/coulomb
C. volt-metre
D. newton/metre

Answer

To determine the SI unit of electric field intensity, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electric Field Intensity**:
Electric field intensity (E) at a point in space due to a charge (Q) is defined as the force (F) experienced by a unit positive charge placed at that point. Mathematically, it is expressed as:
\[ E = \frac{F}{q} \]
where \( F \) is the force acting on the charge \( q \).

2. **Force Between Charges**:
According to Coulomb's law, the force between two point charges \( Q_1 \) and \( Q_2 \) separated by a distance \( r \) is given by:
\[ F = \frac{1}{4 \pi \epsilon_0} \frac{Q_1 Q_2}{r^2} \]
Here, \( \epsilon_0 \) is the permittivity of free space.

3. **Substituting Force in Electric Field Intensity**:
If we consider a unit positive charge \( q = 1 \, \text{C} \), the electric field intensity can be rewritten as:
\[ E = \frac{F}{1} = F \]
Therefore, the unit of electric field intensity is the same as the unit of force.

4. **Unit of Force**:
The SI unit of force is the Newton (N). Thus, we have:
\[ E = \text{Newton} \]

5. **Unit of Charge**:
The SI unit of electric charge is the Coulomb (C).

6. **Final Expression for Electric Field Intensity**:
Since electric field intensity is defined as force per unit charge, we can express the unit of electric field intensity as:
\[ E = \frac{\text{Newton}}{\text{Coulomb}} = \text{Newton per Coulomb} \, (N/C) \]

7. **Conclusion**:
Therefore, the SI unit of electric field intensity is:
\[ \text{Newton per Coulomb} \, (N/C) \]