Question

Electric force of 80 N acts between two point charges. When these charges are placed in a dielectric medium, then electric force becomes 8 N. Dielectric constant of the medium will be

• A. 0.1
• B. 10
• C. 16
• D. 640

Hint:

For any medium other than a vacuum, the dielectric constant \(K\) is always greater than 1. This means the electric force between charges is always weakened when they are placed in a dielectric material. If you get an answer for K that is less than 1, you have likely inverted the formula.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The electric force between two point charges changes when they are placed in a dielectric medium instead of a vacuum (or air). The dielectric constant (K), also known as relative permittivity (\(\epsilon_r\)), is a measure of how much a dielectric material reduces the electric field strength. The force in the medium is inversely proportional to the dielectric constant.

Step 2: Key Formula or Approach:
The relationship between the electric force in a vacuum (\(F_{\text{vacuum}}\)) and the electric force in a dielectric medium (\(F_{\text{medium}}\)) is given by the formula: \[ K = \frac{F_{\text{vacuum}}}{F_{\text{medium}}} \] where \(K\) is the dielectric constant of the medium.

Step 3: Detailed Explanation:
We are given the following values:
The initial electric force in air (which is approximately a vacuum), \(F_{\text{vacuum}} = 80 \text{ N}\).
The electric force when placed in the dielectric medium, \(F_{\text{medium}} = 8 \text{ N}\).
Using the formula from Step 2, we can calculate the dielectric constant \(K\): \[ K = \frac{80 \text{ N}}{8 \text{ N}} \] \[ K = 10 \]

Step 4: Final Answer:
The dielectric constant of the medium is 10. Therefore, option (B) is correct.