Wednesday, July 26, 2017

Capacitors and capacitance (physics)

CAPACITORS AND CAPACITANCE  
A combination of two conductors placed close to each other is called a capacitor. One of the conductors is given positive charge and the other is given negative charge. The conductor with the positive charge is called positive plate and the other is called negative plate. The charge on positive plate is called the charge on the capacitor and the potential difference between the plates is called the potential of the capacitor. 
For a given capacitor,the charge Q on the capacitor is directly proportional to the potential difference V between the plates. 
   Q=CV
The proportionality constant C is called the capacitance of the capacitor. It depends on the shape, size and geometrical placing of the conductors and the medium between them. 
The SI unit of capacitance is coulomb per volt which is written as farad. The symbol F is used for it. This ia large unit on normal scales and microfarad is used more frequently. 
To put equal and opposite charges on the two conductors they may be connected to the terminals of a battery .Here we state the following properties of an ideal battery. 
(a) A battery has two terminals.
(b)  The potential difference V between the terminals is constant for a given battery. The terminal with higher potential is called the positive terminal and that with lower potential is called the negative terminal. 
(c)  The value of this fixed potential difference is equal to the electromotive force or emf of the battery. If a conductor is connected to a terminal of a battery ,the potential of the conductor becomes equal to the potential of the terminal.