Topic 11 - Static Electricity

Question 1

SP11a - Describe the movement of electrons and the charges involved when you rub an acetate rod with a cloth.

Answer 1

• Both objects start off as neutral.
• Electrons move from the acetate rod to the cloth so the acetate rod ends up positive and the cloth ends up negative.

Question 2

SP11a - Describe the movement of electrons and the charges involved when you rub an polythene rod with a cloth.

Answer 2

• Both objects start off as neutral.
• Electrons move to the polythene rod from the cloth so the polythene rod ends up negative and the cloth ends up positive.

Question 3

SP11a - Describe what will happen when you hang two rods next to each other with:

• Positive and positive charges
• Positive and negative charges
• Negative and negative charges

Answer 3

• Repel
• Attract
• Repel

Question 4

SP11a - Explain how charging with induction works. (Use a balloon a jumper and a wall as an example)

Answer 4

• If you rub a balloon against a jumper, the friction causes electrons to transfer from the jumper to the balloon.
• The balloon now has a negative charge
• When brought close to a wall, the negative charge of the balloon repels the electrons in the wall
• The protons are brought closer to the surface of the wall as they are attracted to the balloons negative charge
• The balloon is attracted to the positive charge on the surface of the wall causing it to stick
• The wall has an induced charge

Question 5

SP11b - How might you become charged while walking along a carpet?

Answer 5

Friction between your feet and the floor and slight friction between you and the air builds up charges.

Question 6

SP11b - After gathering charge, how may you become discharged?

Answer 6

• By touching something made of conducting material, the electrons will jump to the object and head to the ground.
• You may experience a small electric shock

Question 7

SP11b - Explain how lightning occurs.

Answer 7

• Static electricity builds up in clouds due to friction between ice and water particles in air currents.
• The negatively charged particle move towards the bottom of the cloud.
• As the ground is neutral, it is relatively positive to the cloud and so when the charge in the clouds is too great, they jump to the ground to discharge.
• This produces a spark which is lightning.

Question 8

SP11b - How may a tall building protect an area from lightning.

Answer 8

• A tall building may install a lightning conductor.
• This would be a metal structure that would be the tallest structure in an area that runs through the centre of the building to the ground.
• This means that a cloud will discharge through this which wont affect the surrounding areas.

Question 9

SP11b - Explain the safety feature that protects airline tankers and aircrafts.

Answer 9

• As high amounts of fuel pass through the nozzle at a fast rate, this build up friction which charges the fuel droplets.
• Once they have built up a great charge they want to discharge.
• This would create a spark which would light the fuel causing an explosion.
• The bonding line is attached which earths the aircraft so that the charge flows through easily to the ground without any spark.

Question 10

SP11b - Why don’t cars need a bonding line at petrol stations.

Answer 10

The pipes and the car’s tyres earth the car already.

Question 11

SP11b - Name some uses of static electricity.

Answer 11

• Electrostatic sprays:
  
  • Spray paint
  • Pesticide
• Printers
• Electrostatic precipitators

Question 12

SP11b - How do electrostatic sprays work?

Answer 12

The nozzle contains electrodes which negatively charge the spray droplets. This leads to two things:

1. The like charge between all droplets spread them out
2. The negative charge attracts to the relatively positive object/crop and then charges it by induction to stick

Question 13

SP11b - Name some advantages of electrostatic sprays

Answer 13

• Since they spread out there is wide coverage
• Since they attach through static induction there is even coverage
• Since all the droplets attach, less spray is wasted

Question 14

SP11c - What is a force field, and what is an electrostatic field?

Answer 14

• A force field is the area around an object in which an object will experience a force and so…
• An electrostatic field is the area around an object where a charged object will experience a force

Question 15

SP11c - What does a negative and a positive point charge diagram look like

Answer 15

• Both are a dot with equally spaced lines originating form the centre.
• In a positive one there are arrows away and in a negative one they are towards

Question 16

SP11c - What will be the difference between two field diagrams if one has a stronger charge

Answer 16

There will be more lines as they will be closer together

Question 17

SP11c How do you know where the field is strongest?

Answer 17

Where the lines are closest together

Question 18

SP11c - What are the four rules about field lines?

Answer 18

• Lines never cross
• The closer the lines are is where the field is strongest
• Start on the positive charge and end on the negative charge
• Shows the direction of force on an object

Question 19

SP11c - What do two oppositely charged parallel plates form?

Answer 19

A uniform parallel electrostatic field

Question 20

SP11c - If an alpha particle is placed into a uniform parallel field where will it move?

Answer 20

Towards the negatively charged plate.