static electricity

Question 1

State the law of electrostatics

Answer 1

Like charges repel and unlike charges attract. The force of attraction and repulsion increases as distance between charges decreases.

Question 2

What can you conclusively say if two objects attract or repel each other?

Answer 2

attract: at least one of the objects is charged
repel: both objects are charged and have like charges

Question 3

State the 2 factors affecting the strength of forces between 2 objects

Answer 3

• amount of charge in both objects
• distance between the centres of both objects

Question 4

How do you explain whether an object will be attracted/repelled by a positively charged object X? (if the object has two oppositely charged hemispheres)

Answer 4

The object will be repelled/attracted as the attractive force between the positive charges on X and the negative charges on the object is weaker/stronger than the repulsive force between the positive charges on X and the positive charges on the object, since the positive/negative charges on the object are closer to the positive charges on X than the negative/positive charges on the object are.
As such, the net force acting on the object is repulsive from/attractive toward X.

Question 5

Distinguish conductors and insulators

Answer 5

conductor: allow electric charges to flow through them easily
insulator: do not allow electric charges to flow through them easily

Question 6

Define electric field

Answer 6

a region where an electric charge experiences a force

Question 7

Define electron affinity

Answer 7

tendency to acquire more electrons

Question 8

Explain charging by friction

Answer 8

Electrons are rubbed off from object A which becomes positively charged and deposited on object B which becomes negatively charges

Question 9

Explain how a bunsen burner can neutralise charge

Answer 9

the flame ionises the air which serves as a conductor. the charges will be neutralised by the ionised air.

Question 10

Explain the process of charging 2 insulated metal spheres

Answer 10

1. two neutral spheres are on insulating stands touching each other
2. when a negative (polythene) strip is brough near A, electrons on A are repelled away from strip and move into B, leaving excess positive charges at the end of A nearer to strip
3. while the strip is kept in position, A and B are separated,
4. remove the strip. A is now positively-charged, B is negatively-charged, as they have an equal amount of opposite charges redistributed throughout A and B when far apart

Question 11

Explain how to obtain positive charges by induction

Answer 11

1. negative (polythene) strip brought near neutral metal sphere mounted on insulating stand. as negative charges are repelled to other side leaving behind excess positive charges at the LHS, positive charges are induced on LHS and negative charges are induced on RHS
2. conductor is earthed by touching it with a finger. as positive charges in sphere are attracted to negative charges of strip, excess electrons at the other side of sphere flow down to earth
3. finger is removed from conductor
4. strip is removed
5. charges are redistributed due to law of electrostatics leaving behind a positively-charged sphere