Question

(a) Consider two identical metal plates of area A, separated by a non-conducting material which has a thickness d. They are connected in a circuit with a battery and a switch, as shown above. When the switch is open, there is no excess charge on either plate. The switch is then closed. What will happen to the amount of net excess charge on the metal plate that is attached to the negative terminal of the battery? What will happen to the amount of net excess charge on the plate that is connected to the positive terminal of the battery? Explain.

(b) Can excess charges on one plate of a charged parallel plate capacitor interact with excess charges on the other plate? If so how? Note: To say that two charges interact is to say that they exert forces on each other from a distance.

(c) Is there any limit to the amount of charge that can be put on a plate? Explain.

(d) Use qualitative reasoning to anticipate how the amount of charge a pair of parallel plate conductors can hold will change as the area of the plates increases. Explain your reasoning.

(e) Do you think that the amount of net excess charge a given battery can store on the plates will increase or decrease as the spacing, d, between the plates of the capacitor increases? Explain

Answer 1

1. Obviously, initially there can be no charge on the plates. After, the switch is closed

1.Charges on the plate which is connected to the negative terminal will have negative net charges.

               ie) Electrons from the battery are transferred to the plate     

2.Charges on the plate which is connected to the positive terminal will have positive net charges

               ie) Electrons from the plate are transferred to the battery.

(b) Yes, obviously it is possible. Because, there is a non conducting material between the plates, so that the material can allow the electric field passes through it, it means there can be forces between the charges on the plates.

(c.) Yes, definitely, there are limitations.

•     The parallel plate system can act as a parallel plate capacitor, and connected to a constant voltage source. Charge in the capacitor is given by ; where the V is voltage of the source. For a particular capacitor the above parameters are constant. Therefore, the amount of charge on the plates have a limit, which depends on the parameters of the parallel plate system.

(d) is the amount of charge that can be carried by a capacitor, from this relationship, it is obviously . So, that if we increase the area of the plate, the amount of charge in the capacitor or in other words amount of charge on the plate will increase.

(e) Yes, definitely it can be varied by changing the distance. From the formula , it is clear that the charge Q and the distance d are having a disproportional relationship.