A potential of 400 V is applied to a capacitor, the plates of which are 4 mm apart. The strength of electric field is

Let's break down this problem step-by-step to understand how to find the electric field strength.

What is Electric Field Strength?
The electric field strength (often denoted by 'E') tells us how strong the electric force is at a particular point.
Think of it like this: the higher the electric field strength, the stronger the force a charge would feel if placed there.

The Relationship Between Potential and Electric Field
When we have a uniform electric field (meaning the field is the same strength and direction everywhere), there's a simple relationship between the potential difference (voltage, 'V') and the electric field strength ('E'):

E = V / d

Where:
* 'E' is the electric field strength (what we want to find)
* 'V' is the potential difference (voltage) between the plates
* 'd' is the distance between the plates

Applying the Formula to Our Problem
We're given:
* V = 400 V (potential difference)
* d = 4 mm = 0.004 m (distance between plates - we need to convert mm to meters!)

Now, plug these values into the formula:
E = 400 V / 0.004 m
E = 100000 V/m
E = 100 kV/m (Kilovolts per meter)

Therefore, the correct answer is Option A: 100 kV/m