What effect does a dielectric have on the capacitance of a capacitor?
Correct answer: A. Increases by k
- A. Increases by k
- B. Has no effect
- C. Decreases by k
- D. Increases by k/2
Explanation
Introducing a dielectric in a capacitor causes a decrease in the electric field, and hence the voltage. The charge stored on the plate remains unchanged.As C = Q/V,decreasing V causes an increase in capacitance.The capacitance of a parallel plate capacitor is given by:capacitance C = (area of plate) (permittivity of free space) / (distance between the plates) = Aεo/d ..........(1)Introducing the dielectric, the capacitance becomes:capacitance Cm = (area of plate) (permittivity of medium) / (distance between the plates) = Aεm/d .......... (2)The relative permittivity is given by:k = εm/εoor εm = kεoPutting (εm = kεo ) in equation 2:Cm = Akεo/d = Aεo/d x kCm = C x kHence, the introduction of dielectric causes the capacitance to increase by k times.
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Electrostatics describes forces between charges through Coulomb's law, electric fields and field intensity, then uses electric potential to measure energy per unit charge. Capacitors store charge and electrical energy, with capacitance depending on geometry and dielectric material, not simply on the amount of charge present.
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