Electric Charge And Electrification - Practice Questions & MCQ

Conductors and insulators: 

When a plastic rod rubbed with cat fur and is connected with a neutral pith ball via a copper wire,  it is observed that pith ball gets negatively charged. But when a plastic rod rubbed with cat fur is connected with a neutral pith ball via a rubber the pith ball remains neutral. That is copper allows passage of charge and rubber does not. The materials which allows passage of electricity are known as conductors and the materials which do not allow passage of electricity is known as insulators.

Methods of charging 

1. By Friction: When two bodies rub together both positive and negative charges in equal amounts appears simultaneously due to transfer of electrons. When a glass rod is rubbed with a silk cloth, the electrons are transferred from glass rod to silk. The glass rod becomes positively charged and the silk rod becomes negatively charged.

2. By induction: When a charged body is brought near an uncharged body, one side of the neutral body becomes oppositely charged while the other side has the same charge. For example, when a positively charged glass rod is brought near a paper the paper gets attracted, this is because of the rod attracts the electrons of paper towards it so that the edge of the paper near the rod becomes negatively charged and the other end becomes positively charged due to deficiency of electrons. 

3. By conduction: When two conductors are brought in contact, the charges will spread over both the conductors. For example, when a negatively charged plastic rod is brought in contact with a neutral pith ball some of the electrons of the rod are transferred to the pith ball and the pith ball also becomes negatively charged.