Static Electricity

Question 1

How are materials given an electric charge?

Answer 1

transfer of electrons from place to place

Question 2

Examples of good conductors

Answer 2

• metals (copper/silver/gold)

- carbon

Question 3

atomic structure of conductors

Answer 3

• outer electrons held loosely by nucleus

- electrons easily drift towards positive charge

Question 4

examples of good insulators

Answer 4

• plastic
• air
• rubber
• glass
• dry cut wood

Question 5

atomic structure of insulators

Answer 5

• outer electrons held tightly by nucleus

- electrons cannot drift easily

Question 6

what force charges polyethene when rubbed with a woollen cloth?

Answer 6

friction

Question 7

how does friction affect the charges of polyethene/cloth?

Answer 7

• friction pulls electrons from cloth onto polyethene
• polyethene gains negative charge
• cloth becomes positive: doesn’t have enough electrons to balance out protons

Question 8

how does friction affect the charges of acryclic/cloth?

Answer 8

• friction pulls electrons from acryclic to cloth
• acryclic becomes positive: not enough electrons to balance the protons
• cloth gains negative charge

Question 9

why are rods placed on watchglass?

Answer 9

reduces friction

acts as an insulator to stop electrons leaving the rod

Question 10

uses of static electricity

Answer 10

• electrostatic precipitators
• spray painting
• photocopiers/printers

Question 11

What are electrostatic precipitators used for?

Answer 11

• clean dust particles from chimney to preven them entering atmosphere

Question 12

How is static electricity used in electrostatic precipitators ?

Answer 12

• dust particles pass through positively charged mesh
• particles become positive
• pass by negative charged plates so stick to plates

Question 13

How is static electricity used in spray painting a bike frame?

Answer 13

• bike frame = (+)
• nozzle given a (-) charge so the droplets are (-) and repel and disperse
• droplets attract to bike frame and reach all areas of bike

Question 14

How is static electricity used in photocopiers/laser printers?

Answer 14

• corona wire sprays electrons onto drum
• laser shines onto drum which gives energy to electrons it hits to escape
• pattern of electrons left in shape of electrons
• positively charged toner dust sticks to charged part of drum
• toner rolled onto printing paper and is heated to bond toner particles onto paper
• discharge lamp removes electrons from drum to start cycle again

Question 15

Dangers of static electricity

Answer 15

• electric shock
• sparks passing through flammable materials
• microchips

Question 16

How are sparks formed?

Answer 16

electrons jump through air if there is a high p.d.

• 10kV is needed for electrons to pass through a centimetre of dry air
• 100 MV is needed for a lightning bolt to occur

Question 17

examples of flammable materials

Answer 17

• aircraft fuel/ petrol vapour
• fine powdered flour in a mill (have a lot of energy so can easily react with oxygen)
• anaesthetic gases used in operating theatres

Question 18

how are fires prevented when fuelling aircraft?

Answer 18

• aircraft is electrically earthed to discharge them

Question 19

how are micro-chips affected by static electricity?

Answer 19

• compononents easily charged by static which can destroy components

Question 20

how is static components prevented?

Answer 20

• wear earthing straps

- work on earthed metal benches

Question 21

what is the effect of eathing strips?

Answer 21

prevent large charges building up