electric charge | quantization of charge | additivity | conservation of charge | Coulomb's law by advguruji

Electric charge

It is defined as the fundamental quantity of electricity.

Or,

It is referred as a particle which experience force when placed in an electric field or when it is moving in a magnetic field.

The SI unit of electric charge is coulomb 'C'. Its dimension is 'AT'.

It is of two types:

Note: In reality, the charge of a down quark is '-e/3' and charge of an upquark is '+2e/3', but they always found in collection and not in singular form.

Properties of electric charge

1. Additivity of charge

The net charge of any system is the algebraic sum of all the charges present in the system. For example, a body contains charges as shown in figure...

2. Conservation of charge

The total charge of any isolated system remains conserved i.e., it can neither be created nor be destroyed but it can only be transferred from one place to another inside the system.

For example,

when you rub a plastic scale on your scalp, the charge in the form of electrons is transferred from hairs to the scale but new charge is not created.

3. Quantization of charge

Any free charge is equal to the integral multiple of the fundamental unit of charge.

                   q = ne

Coulomb's law

According to this law, the electrostatic force between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.

(Similar to universal law of gravitation)

[   F = k.q1.q2/r²   ]

where,    k = 1/4πεο

                = 9 × 10⁹ Nm²/C² (constant)

Note :- Like charges repel each other and unlike charges attract each other.

Q2: Find the force of attraction between two charges of 5μC and -10μC separated by 10 cm.

Ans. (( DO YOURSELF ))

Q3: Find the ratio of electrostatic forces between two charges of 20nC and 5nC separated by 1 m.

Ans. (( DO YOURSELF ))

Q4: State the limitations of coulomb's law.

Ans. Limitations of coulomb's law :-

(1) It is only applicable when the charges are at rest.

(2) It is not applicable on irregular shape charges where distance between them is hard to calculate.

Coulomb's law in vector form

                      

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