A Point Charge in an Electric Field

Bismillah..

This sub topic will tell you about what happen to a charged particle (q) when it is in electric field by other stationary or slowly moving charges.

So, this is actually happen to the charged particle. there is an electrostatic force acting on that particles. We can know the electrostatic force by:

F = qE

where:

F : electrostatic force

q : charge of the particle

E : electric field

This equation told us:

The F acting on charged particle located in external E has direction of E if charge q of particle is +ve and has opposite direction if q is 

-ve

• Measuring the elementary charge

Milikan experiment proof that charge is quantized. It is also can determine the effect of charge q

Value of q can always determine using equation :

q = ne

where:

q : charged particle

n : 0, +- 1, +-2, +-3, ... ,

e : elementary charge (1.60 × 10^-19 C)

This is the video that show the Millikan experiment, enjoy it!

To understand the experiment of Millikan’s we would learn how he performed things one by one step taken by him:

1. Initially he uses an atomic sprayer to spray the tiny oil particle in the first chamber.
2. He lets these oil drop falls under the influence of the gravitational field, until they acquire the terminal velocity.
3. Using the terminal velocity as input he calculated the mass of the oil drop.
4. Next he illuminated the second chamber with the X rays and allowed the oil drop to fall freely. Due to the X rays the chamber is illuminated and the air gets ionized. This ionized air comes in contact with the oil drop.
5. The electron on the air particle attaches itself to the oil drop and hence now the oil drop is charged.
6. He then attached the battery to the two electrodes and apply the enough voltage to counter balance the force of gravity.
7. By using the value of the applied uniform electric field, he was able to estimate the charge associated the oil drop.
8. He then repeated the same experiment with different charge density and always finds that the charge of oil drop(s) obtained is the multiple of the 1.59 x 10^-19 C.
9. He then concluded that the charge of the electron is equal to 1.59 x 10^-19 C.

• Electrical breakdown and sparking

If electric field, E exceed its critical value, the air undergoes electrical breakdown,
where electrical breakdown is a process where the field remove electrons from atoms in air
The air then begin to conduct electric current. As they move, they collide with any atoms cause the atoms to emit lights. The path is called sparks.