1 of 14

16.2 How do we charge objects?

Charging Objects by Rubbing

Illustration of charging by rubbing

When an amber rod is rubbed with fur, it results in the transfer of a certain amount of negative charge (electrons) from the fur to the amber as shown above
Hence the amber becomes negatively charged
On the other hand, the fur has lost the same amount of electrons and becomes positively charged. At no time during this process is charge ever created or destroyed.

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

2 of 14

Illustration of charging by rubbing

When charge is transferred from one object to another, it is generally due to the movement of electrons
As a piece of fur rubs across an amber rod, some of the electrons that were originally part of the fur are separated from their atoms and deposited onto the amber

16.2 How do we charge objects?

Charging Objects by Rubbing

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

3 of 14

Illustration of charging by rubbing

The atom that loses an electron is now a positive ion, and the atom that gains an electron is a negative ion
This is known as charging by rubbing

16.2 How do we charge objects?

Charging Objects by Rubbing

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

4 of 14

Charging Objects by Induction

To induce a negative charge on a conductor	To induce a positive charge on a conductor
Step 1: Two neutral, insulated metal spheres, P and Q, are placed touching each other	Step 1: Two neutral, insulated metal spheres, P and Q, are placed touching each other

Table below shows how objects can be charged by induction

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

5 of 14

To induce a negative charge on a conductor	To induce a positive charge on a conductor
Step 2: When a negatively charged rod is brought near P, the electrons (negatively charged) on P are repelled away from the rod. They move onto Q. Thus P is left with a positive charge	Step 2: When a positively charged rod is brought near P, the electrons (negatively charged) from Q are attracted to the rod. They move onto P. Thus P is left with a negative charge

16.2 How do we charge objects?

Charging Objects by Induction

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

6 of 14

To induce a negative charge on a conductor	To induce a positive charge on a conductor
Step 3: Q is then separated from P while the negatively charged rod is kept in position	Step 3: Q is then separated from P while the positively charged rod is kept in position

Charging Objects by Induction

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

7 of 14

To induce a negative charge on a conductor	To induce a positive charge on a conductor
Step 4: The rod is then removed. P and Q now possess equal amounts of opposite charge. P and Q have been charged by induction	Step 4: The rod is then removed. P and Q now possess equal amounts of opposite charge. P and Q have been charged by induction

Charging Objects by Induction

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

8 of 14

Charging Objects by Earthing

To obtain a negative charge on a conductor	To obtain a positive charge on a conductor
Step 1: A positively charged rod is brought near to a neutral, insulated conductor. The electrons (negatively charged) are attracted towards the rod at end P leaving a positive charge at the other side of the conductor	Step 1: A negatively charged rod is brought near to a neutral, insulated conductor. The electrons (negatively charged) are repelled, leaving a positive charge at the side of the conductor near the rod

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

9 of 14

To obtain a negative charge on a conductor	To obtain a positive charge on a conductor
Step 2: The conductor is then earthed by touching it with a finger. This closed path allows electrons to flow from the Earth to neutralise the positive charge at Q	Step 2: The conductor is then earthed by touching it with a finger. This closed path allows electrons to flow from the conductor to the Earth.

Charging Objects by Earthing

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

10 of 14

To obtain a negative charge on a conductor	To obtain a positive charge on a conductor
Step 3: Finger is removed. The conductor is left with a negative charge.	Step 3: Finger is removed. The conductor is left with a positive charge

Charging Objects by Earthing

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

11 of 14

To obtain a negative charge on a conductor	To obtain a positive charge on a conductor
Step 4 : The positively charged rod is then removed. The negative charge is redistributed evenly on the conductor	Step 4 : The negatively charged rod is then removed. The positive charge is redistributed evenly on the conductor

Charging Objects by Earthing

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

12 of 14

Crazy Action of Paper

Earlier on, we learnt that unlike charges attract

To explain the attraction between a charged body and an uncharged (neutral) body, we use the process of induction

16.2 How do we charge objects?

Illustration of the erratic movement of paper under a charged Perspex rod

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

13 of 14

A Perspex rod is charged positively by rubbing it with a woollen cloth.

When the rod is held above a small piece of paper which is neutral, a negative charge is induced at the end of the paper nearer to the rod while a positive charge is induced at the other end

Since unlike charges attract and like charges repel, an attractive force F₁ and repulsive force F₂ both act on the paper

As the negative charge is nearer to the rod than the positive charge, F₁ is greater than F₂

Crazy Action of Paper

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity

14 of 14

Illustration of the erratic movement of paper under a charged Perspex rod

Thus, the paper moves towards the rod
When the paper touches the rod, it loses its negative charge to the rod and becomes positively charged
Since like charges repel, the paper is repelled from the rod. This explains the erratic movement of the paper under the rod

Crazy Action of Paper

16.2 How do we charge objects?

Section 5 ❘ Electricity and Magnetism

16

Static Electricity