Question

Explain why capacitance ?C depends neither on the stored charge ?q nor on the potential difference ?V between the plates of a capacitor.

Capacitance is determined only by the physical properties of the capacitor.

The stored charge ?q and the potential difference ?V are independent of the size and shape of the capacitor.

The net charge on a capacitor is zero, and therefore the potential difference ?V cancels.

The stored charge ?q is inversely proportional to the potential difference ?.

A defibrillator containing a 10.7 ?F10.7 μF capacitor is used to shock the heart of a patient by holding it to the patient's chest. Just prior to discharging, the capacitor has a voltage of 12.5 kV12.5 kV across its plates. How much energy is released into the patient?

Answer 1

The expression for the capacitance of the capacitor is, c=보 Here, Eo is the permittivity of the free space, Ά is the area of the plates and d is the distance between the plates Hence, from the above equation, the capacitance is independent of charge and the voltage. The capacitance is also defined as, TV The ratio increases, to keep the ratio is constant. It the voltage in the capacitor is increased, the voltage also constant.

Hence, the capacitance of the capacitor is determined by the physical characteristics of the capacitor The expression for the energy stored in the capacitor is, Cr2 Substitute the values in the above equation. Cr2 (10.7x10 F)(12.5x10' v) 835.93 J