Question

A dielectric slab is inserted between the plates of an isolated capacitor. The force between the plates will

• A. increase
• B. remain unchanged
• C. decrease
• D. become zero

Hint:

Inserting a dielectric increases capacitance but decreases the force between the plates, as the electric field is reduced.

Answer 1

The Correct Option is C

Step 1: Recall the effect of a dielectric.
When a dielectric material is inserted between the plates of a capacitor, it increases the capacitance by a factor of the dielectric constant (\( \kappa \)). For an isolated capacitor, the charge \(Q\) remains constant.
Step 2: Force between the plates.
The force \(F\) between the plates of a capacitor is given by: \[ F = \frac{1}{2} \frac{Q^2}{A \epsilon_0} \left( \frac{1}{d^2} \right) \] When a dielectric is inserted, the electric field between the plates decreases, thus reducing the force between the plates. Step 3: Conclusion.
Thus, the force between the plates will decrease.
Final Answer: \[ \boxed{\text{decrease}} \]