We have a capacitor let's say of capacitance C and is charged by Voltage say V. Then the voltage is disconnected and a dielectric of dielectric constant say k is inserted fully between the plates of parallel plate capacitor. We are asked to find the change in charge stored by the capacitor and change in voltage.
Now what I am not getting is why does charge stored in capacitor remain constant. The surface charge density decreases due to polarisation of dielectric and so the net charge on the plates should decrease yet we are considering charge to be constant.
Please correct me😶😶.
[Physics] Why does charge on a capacitor remain constant when dielectric is fully inserted between the plates of the capacitor
capacitanceconservation-lawselectric-circuitselectrostatics
Best Answer
Because you disconnected the voltage source. It's meant to be implied that the capacitor is disconnected from all external circuits. Therefore there's nowhere for the charge to go. And since charge is a conserved quantity, that means the charge on the capacitor plate must remain constant.
The charge associated with the polarization only compensates for some of the charge on the plate, it doesn't remove it. The charge associated with polarization is in the dielectric, and the charge on the plate is on the plate.