Question

Why capacitors doesnot allow rate of change of voltaga?

Answer 1

No current ever flow through capacitor. When a voltage is applied, dielectric gets polarized, and resulting dipoles orient themselves under the effect of electric field. Positive poles if these dipoles are attracted towards negative plate, and negative poles towards positive plate.

This creates a net positive charge layer near positive terminal plate. To maintain equilibrium, positive charges accumulate on the electrode. Similarly negative charge gets accumulated near negative plate — which is effectively same as removal of positive charges. So an observer will see this as current entering from one terminal znd exiting from the other.

This process takes some time before a voltage appears across capacitor, depending upon the rate of charge flow (current). Voltage develops across capacitor as charge appears on its plates

Capacitor thus does not change voltage across its terminals due to this process of maintaining charge equilibrium. Higher the current, faster is voltage rise across capacitor.

Answer 2

Because every half cycle capacitorcharge is replenished and when incoming voltage decreases capacitortakes over and gives out it's charge as per demand. ... Rate of electrical charge transfer is equivalent to electrical current, so to cause an instantaneous change in the voltageacross a capacitor.