Static Electricity

Question 1

SP11a Charges and static electricity

Explain how insulators can be charged via friction

Answer 1

• Plastics make good insulators as they can collect charge.
• The charges cannot flow through the plastic into other materials.
• When you rub an acetate rod onto a dry duster, some electrons move from the acetate to the duster.
• Since electrons are negatively charged, the duster gains a negative charge.
• When you rub a polythene rod with a duster, electrons move from the duster onto the polythene, and the opposite situation occurs.

Question 2

SP11a Charges and static electricity

Explain why hair strands stick up when charged.

Answer 2

• The charge is not able to flow away to surroundings.
• Since all the hairs have the same charge, they repel eachother.

Question 3

SP11a Charges and static electricity

Explain the process of charging by induction
( Use balloons for example )

Answer 3

Note: A charged object can affect the distrubition of charges on an uncharged object.

1. If a negatively charged balloon is brought near a wall, the negatively charged electrons in the wall are repelled.

2. This causes the surface of the wall to become positively charged.
- No charged have been transferred from the balloon and so we say the wall has been induced.

3. This is called charging by induction

Question 4

SP11b Dangers and uses of static electricity

Explain how shocks occur from everyday objects in terms of moving electrons.

Answer 4

This happens as;
- When you walk across some types of carpets, you may end up with an unbalanced electric charge.

• If you then touch a conductor, such as a metal tap, electrons flow between you and the tap. There may also be a spark and you may feel a small shock.
• The electrons flow in whichever direction removes the excess charge, so you can either be discharged or earthed

Question 5

SP11b Dangers and uses of static electricity

Explain the process of how lightning occurs in reference to the movement of electrons.

Answer 5

This happens as;
- Static electricty builds up in the clouds due to friction between particles of ice/water moved by air currents

• When the charge is large enough, charged particles travel through the air between the cloud and earth.
• This causes both lightning and thunder. Lightning can be dangerous so to discharge clouds safely, buildings are earthed by having lightning conductors made of thick metal.
• This works as it provides a path with a low resistance for the electrons to flow towards the metal rod and into the ground.

Question 6

SP11b Dangers and uses of static electricity

Describe some of the dangers of sparking and explain how earthing can be used to prevent these.

Answer 6

1. Fuel vapour ( Aircrafts )
- Sparking could be an issue when their is fuel vapour that could ignite.
- A charge could build up when fuel flows through the pipe.
- To prevent a spark between a fuel pipe and an air craft, a ‘bonding line’ is connected to earth the aircraft before refuelling.

2. Petrol filling
- Cars are earthed through their tyres, which contain a form of carbon that makes them conducting, and you are earthed when you touch the metal of the car, or the pump.

Question 7

SP11b Dangers and uses of static electricity

Describe some uses of static electricity

Answer 7

1. Electrostatic spraying
- For example, when spraying crops with insecticide, electrodes on the spray nozzle charge the spray droplets as they pass.

• The charged droplets spread out because they repel eachother and then they are attracted to the plant via induction
• This means the spray spreads all over the plants, even beneath it, meaning less spray has to be used as it won’t fall on the floor either.

Question 8

SP11c Electric fields

Describe what is ment by an electric field

Answer 8

• A charged object has a force field around it called an electric field.
• Another charged object placed in the field will experience a force.

Question 9

SP11c Electric fields

Describe the shape and direction of electrical fields;
A) Around a point charge
B) Between parrallel plates

Answer 9

A) Around a point charge the lines;
- Never cross
- Show where the field is strongest ( which is where the field lines are the closest )
- Face outwards if positive point charge, inwards if negative.

B) Between parrallel lines;
- The electric field between 2 parrallel place is uniform, they are the same in all place
- The field lines go from the positive top plate towards the negative bottom plate.

Question 10

-SP11c Electric fields

Explain how the existence of electrical fields explain the phenomena of static electricity

Answer 10

• When 2 electrical fields interact, if both the objects have the same charge, the field lines will be facing in different directions, causing them to repel.
• However, if they have opposite charges, the field lines will be facing in the same direction, allowing for the forces of attraction to occur.