Electricity: Static Electricity

Question 1

Why can insulators become electrically charged when rubbed together?

Answer 1

• electrons are rubbed from one material onto the other
• the material gaining electrons becomes negatively charged
• the material losing electrons becomes equally positively charged

Question 2

Explain how rubbing an acetate rod with a cloth causes the rod and cloth to become charged. (4)

Answer 2

• friction (between cloth and rod) causes
• electrons to move
• from the acetate rod (to the cloth)
• (net) charge on cloth is now negative
• (net) charge on rod is now positive

Question 3

What can happen when insulating materials are rubbed together?

Answer 3

They can become statically electrically charged.

Question 4

What happens when two identically charged objects are brought close together compared with two oppositely charged objects?

Answer 4

• like charges repel
• opposite charges attract

Question 5

What is an electric field?

Answer 5

A region in which a charged object will experience a non-contact electrical force.

Question 6

Where can electric fields be found?

Answer 6

Surrounding any charged object.

Question 7

Describe the strength of an electrical field in different areas surrounding a charged particle.

Answer 7

• strongest closest to the object
• strength decreases as you move away from the object

Question 8

What happens to the force between two charged objects when they are brought closer together?

Answer 8

The force between them becomes stronger.

Question 9

In situations where sparks are unwanted, what precautions must be taken to prevent the build up of static charge?

Answer 9

Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials.

Question 10

If you rub your hands all over a charged comb, why will it no longer attract your hair?

Answer 10

The electricity has gone to earth.

Question 11

How are sparks caused?

Answer 11

• when there is a high enough potential difference between a charged object and the earth (or an earthed object).
• a high potential difference causes a strong electric field between the charged object and the earthed object
• the strong electric field causes electrons in the air particles to be removed
• air is normally an insulator but when it ionised it is much more conductive, so a current can flow through it
• this is a spark

Question 12

What happens to an acetate rod when it is rubbed by a cloth? What happens to a polythene rod when it is rubbed by a cloth?

Answer 12

Acetate
- electrons move from the rod to the cloth

Polythene
- electrons move from the cloth to the rod