Section 2 - Electricity P2

Question 1

What are the rules about charges?

Answer 1

• opposite charges attract
• the same charges repel
• the forces get weaker as the distance between the two things increases

Question 2

What are the rules about electrical conductors and insulators?

Answer 2

Electrical conductors-conduct charge easily, current can flow
Electrical insulators-don’t conduct charge well, current can’t flow

Question 3

What is a static charge?

Answer 3

A charge which builds up in one place and is not free to move. This is common in insulators.

Question 4

What is a common cause of static electricity, and what does this result in?

Answer 4

Friction- when two insulating materials are rubbed together electrons will move from one to the other.
Resulting in a positive electrostatic charge on one and a negative on the other

Question 5

What sub-atomic particle moves to create a difference in charge?

Answer 5

Electrons(-ve charge)

Question 6

Can static charges occur on conductors?

Answer 6

Yes, cars often get static charges because of the air rushing past losing or gaining electrons

Question 7

How can a charged conductor be discharged safely?

Answer 7

By connecting it to earth with a metal strap, this allows the electrons to even out the charge to neutral

Question 8

What is also built up as static electricity is built up?

Answer 8

The voltage between the object and the earth

Question 9

When is a spark caused?

Answer 9

When the voltage gets large enough, electrons can jump the gap(generally small) between the charged object and the earth(or any earthed conductors nearby).

Question 10

How can you charge acetate and polythene rods?

Answer 10

By rubbing them with a cloth duster

• Polythene rod electrons move from the duster to it
• Acetate rod electrons move from it to the duster

Question 11

What’s a practical using the Gold-Leaf Electroscope which shows if an object carries a charge or not?

Answer 11

• If an object is charged and put near the metal disc the electrons will either be attracted or repelled
• this induces a charge in the metal disc which charges the gold leaves, both gold leaves with have the same charge and therefore will repel each other
• if the leaves don’t move the object isn’t charged

Question 12

What is the Gold-Leaf Electroscope?

Answer 12

The Gold-Leaf Electroscope has a metal disc connected to a metal rod, which has two thin pieces of gold leaf attached.

Question 13

How can you use a suspended rod to test if an object is charged?

Answer 13

-suspend a rod of an unknown charge on a thread and see if there’s attraction or repulsion when you bring your test object close to it

Question 14

What’s the Van de Graaff generator and what is it made up of?

Answer 14

It’s used to demonstrate electrostatic charges.
It’s made up of a rubber belt moving around plastic rollers underneath a metal dome. Therefore a charge is built up on the dome as the belt goes round.

Question 15

Why does the Van de Graaff generator make your hair stand on end?

Answer 15

If you stand on an insulated block and place your hands on the dome, electrons will move between your body and the dome giving your body a charge.
Like charges repel so the charges will spread out as much as possible in your body, the charge is strong enough to make your hairs stand on end and repel each other

Question 16

How is static electricity used in an inkjet printer?

Answer 16

• ink is forced out of a fine nozzle(making it electrically charged)
• these droplets of ink then pass between two oppositely charged metal plates
• the droplets are attracted to one plate and repelled from the other
• the size and direction of the voltage across the two plates change so each droplet hits different places on the paper
• loads of tiny dots make the image

Question 17

How is static electricity used in a photocopier?

Answer 17

• image plate is positively charged, an image of what you’re copying is projected onto it
• white bits make the light fall on the plate and the charge leaks away
• the charged dark areas attract negatively charged black powder which is transferred onto positively charged paper
• the paper is heated to set the powder(so it sticks)

Question 18

Why do synthetic clothes crackle?

Answer 18

When they’re rubbed together, electrons get scrapped off leaving static charges on both items, this leads to them attracting and little sparks form as the charges rearrange themselves

Question 19

How does static electricity cause lightening?

Answer 19

-rain drops and ice bump together in storm clouds, knocking off electrons and leaving the top of the cloud positively charged and the bottom of the cloud negatively charged. This creates a huge voltage and a big spark.

Question 20

How does static electricity create problems with fuel filling?

Answer 20

• as fuel flows out of a filler pipe static can build up

- this can lead to a spark, which can cause an explosion in dusty places

Question 21

How can the problems with fuel filling and static electricity be solved?

Answer 21

• make the nozzles out of metal so the charge is conducted away instead of building up
• have earthing straps between the fuel tank and the fuel pipe