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The capacitance of a capacitor in which a dielectric of dielectric constant 5 has been used is $C$. If the dielectric is replaced by another with dielectric constant 20, the capacitance will become

1. 4C
2. C/4
3. 2C
4. C/2

Correct answer: 4C

Solution

For the same capacitor geometry, capacitance is proportional to the dielectric constant $K$. If $K$ changes from 5 to 20, the capacitance increases by a factor of $20/5=4$. Therefore the new capacitance is $4C$.

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