What must be the potential difference across the plates of the capacitor filled with a dielectric so that it stores the same amount of electrical energy as the empty capacitor?

Explanation:

The electrical energy stored in the empty capacitor is defined as:

Where is the potential difference across the plates of the capacitor and is its capacitance.

The capacitance of the capacitor with a dielectric is given by:

The electrical energy stored in the capacitor filled with a dielectric is:

We have . Thus:

Replacing (1) and solving for :

v=ir = 3x15 =45 v

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explanation: