Physics Made Simple : Electrostatics : Electric Charge

Electric Charge

Electric Charge:

When a plastic comb is moved in dry hair,its starts to attract small pieces of paper.

Similarly,when a glass rod is rubbed with silk cloth ,the rods will start to attract small pieces of paper.

If an ebonite rod is rubbed with a woollen cloth,these rods will also begin to attract small particles.

In these circumstances,we will state that these substances have developed the property of attraction because they have acquired electric charge.

Experiment 1:

Take two glass rods and rub them with silk.

Suspend them horizontally in a line close to each other.

They will repel each other.

Experiment 2:

Take two ebonite rods and rub them with woollen cloth.

Suspend them in a manner similar to Experiment 1.

They will repel each other.

Conclusion:

Like charges repel each other hence,both glass rods have same charge after being rubbed with silk and  ebonite rods have same charge after being rubbed with woollen cloth.

 Experiment 3:

Suspend a glass rod rubbed with silk near to ebonite rod rubbed with woollen cloth.

Both rods will attract each other.

Conclusion:

The charge on ebonite and silk rods is opposite to each other and hence they attract each other.

Infact the glass rod has acquired positive charge by gaining a large number of positively charged particles (protons) after being rubbed with silk  and ebonite rod has acquired a large number of negative charged particles (electrons)/ negative charge after being rubbed with wool.

Mechanism of Charge gained by glass and ebonite rods:

Atom is the fundamental particle of matter.

The atom consists of two parts:

Central part called nucleus that consists of protons and neutrons.

The charge on proton is positive while neutron has no charge.

Second part of atom is called electron that has a negative charge and it moves around the nucleus in an orbit.The atom as a whole is neutral.The magnitude of negative charge of electron revolving around nucleus is equal to positive charge of proton in nucleus .

Due to this attraction between electron and proton,the electron remains attracted to nucleus and thus revolved around it in various orbits.

Number of protons is equal to number of electrons in an atom.

As the distance between electron in orbit increases from nucleus,the force of attraction between electron and proton decreases and hence even if a small external force is applied,the electron can be separated from their respective atom.

When ebonite rod is rubbed with wool,the loosely bound electrons from wool are transferred to ebonite rod and thus it becomes negatively charged.

When glass rod is rubbed with silk,the electrons from glass rod get transferred to silk and hence,glass rod becomes positively charged.

Free electrons:

In metals,electrons in last orbit are so loosely bound that they are not confined to their orbits but instead move freely through whole body of metal.

Such electrons are called as free electrons