MODES OF CHARGING OF A BODY
A body can be charged by various means such as –
1). Charging by friction
2). Charging by conduction
3). Charging by induction
4). Thermionic emission
5). Photoelectric effect
6). Field emission
In this topic we will discuss about these charging methods in detail so tuned with us till end.
CHARGING BY FRICTION
This is one of the simple way of Charging of a body. If we rub a neutral body with other neutral body (at least of then should be insulator) then some electrons will transfer from one body to another body. The body which gains electrons are said to be negatively charged and the body which losses electrons are said to be positively charged.
When we rub a pen in our hairs the same thing occurred as we discussed above, during rubbing some electrons are transferred to the pen and it becomes negatively charged.
CHARGING BY CONDUCTION
There are three types of material in the nature on the basis of numbers of free electrons.
1). CONDUCTOR – These are those materials which have a large numbers of free electrons. Such as – gold , copper , silver etc.
2). INSULATOR OR DIELECTRICS – Insulator or dielectrics are those materials which do not have free electrons. Such as – plastic , wood , paper etc.
3). SEMICONDUCTORS – These are those materials which have less amount of free electrons. Their conductivity are intermediate to conductor and insulators. Such as – CdS , GaAs silicon , germanium etc
When we connect a charged conductor with a neutral conductor then the charge starts flowing from one body to another body. Flow of charge will stop when they attain equal electric potential.
If we connect two charged conductors with each other then the charges start flowing from higher potential energy to the lower potential energy. And the Charge stops flowing when the potential difference between them become zero.
If two identical shaped conductor are kept at large distance and they are connected then they will finally have equal Charges.
CHARGING BY INDUCTION
When a positively charged conductor is taken near to a neutral body then the part which is nearer to the positively charged body became negatively charged and the part which is away from the positively charged body became positively charged. The charged develops in the neutral body is such as the sum of all the charges will zero.
The charging of a body by this method is called charging by induction and the charge produced in this process is called induced charge.
A body can be charged by the process of induction by the following two methods –
METHOD – 1
We know that when we bring a neutral body near to a positively charged body then the part which is away from the positively charged body is positively charged and the part which is nearer to the positively charged body is negatively charged, see figure below.
If we want to make neutral body negatively charged then we have to make earthing from side of positively charged for few seconds. Earthing makes positively charged side neutral.
As positively charged side become neutral then disconnect the earthing and take the positively charged body away. By doing this negatively charge will spread all over the surface and the body becomes negatively charged.
Instead of giving earthing to positively charged side, connect the positively charged side to a another neutral body, by doing this the positive charge will transfer to the neutral body. And that neutral body becomes positively charged.
As shown above
When any metal is heated at high temperatures then some surface electrons are get excited and then they ejected from the metal surface, this ejection of electrons make metals positively charged.
When light of sufficient high frequency is incident on the surface of the metals then some electrons ejected from the metal surface and makes metal positively charged.
When electric field of high magnitude is applied on the surface of the metals then some electrons are ejected from the metal surface and makes metals positively charged.