AQA GCSE Physics 2-4 Static Electricity

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AQA GCSE Physics 2-4Static Electricity

• GCSE Physics pages 160 to 169

July, 2010
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AQA GCSE Specification

• STATIC ELECTRICITY
• 12.5 What is static electricity, how can it be
  used and what is the connection between static
  electricity and electric currents?
• Using skills, knowledge and understanding of how
  science works
• to explain why static electricity is dangerous
  in some situations and how precautions can be
  taken to ensure that the electrostatic charge is
  discharged safely
• to explain how static electricity can be
  useful.
• Skills, knowledge and understanding of how
  science works set in the context of
• When certain insulating materials are rubbed
  against each other they become electrically
  charged. Negatively charged electrons are rubbed
  off one material onto the other.
• The material that gains electrons becomes
  negatively charged. The material that loses
  electrons is left with an equal positive charge.
• When two electrically charged bodies are
  brought together they exert a force on each
  other.
• Two bodies that carry the same type of charge
  repel. Two bodies that carry different types of
  charge attract.
• Electrical charges can move easily through
  some substances, eg metals.
• The rate of flow of electrical charge is
  called the current.
• A charged body can be discharged by connecting
  it to earth with a conductor. Charge then flows
  through the conductor.
• The greater the charge on an isolated body the
  greater the potential difference between the body
  and earth. If the potential difference becomes
  high enough a spark may jump across the gap
  between the
• body and any earthed conductor which is brought
  near it.
• Electrostatic charges can be useful, for
  example in photocopiers and smoke precipitators
  and the basic operation of these devices.

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Electric charge

• Electric charge can be either positive or
  negative.
• In an atom an electron has a negative charge that
  is of the same size as the positive charge of a
  proton.
• Neutrons have no electric charge.
• As an atom has the same number of electrons as
  protons it is uncharged.

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Static and current electricity

• Static electricity describes the situation when
  electric charges remain stationary.
• This occurs best with insulators, for example
  plastic.
• An electric current occurs when electric charges
  are moving from one place to another.
• This occurs best with conductors, for example a
  metal.

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Charging materials

• When certain insulating materials are rubbed
  against each other they become electrically
  charged.
• Electrons are rubbed off one material onto the
  other.
• The material that gains electrons becomes
  negatively charged.
• The material that loses electrons is left with an
  equal positive charge.

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Force and charge

• When a charged object is brought close to an
  uncharged one the two objects attract each other.

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Attraction and repulsion

• Two bodies that carry different types of charge
  attract.
• Two bodies that carry the same type of charge
  repel.
• The law of charges
• LIKE CHARGES REPEL, UNLIKE ATTRACT.

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Choose appropriate words to fill in the gaps
below Static electricity occurs when electric
________ remains ____________ on an object. An
__________ object can be charged by __________ it
with another insulator. One of them gains
________ and becomes negatively charged. The
other becomes equally __________ charged. The law
of charges states that like charges _______,
unlike _________.
charge
stationary
insulating
rubbing
electrons
positively
repel
attract
WORD SELECTION
insulating
attract
repel
stationary
electrons
positively
charge
rubbing
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Electrical chargesNotes questions from pages 160
161

1. Give two examples of static electricity.
2. Explain how atoms may become charged.
3. Draw diagrams and explain how polythene and
   perspex rods can become charged by friction.
4. With the aid of a diagram describe an experiment
   to show that like charges repel and unlike
   charges attract.
5. Copy and answer questions (b) and (c) on page
   161.
6. Copy the Key Points on page 161.
7. Answer the summary questions on page 161.

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Electrical charges ANSWERS

• In text questions
• (b) It loses electrons
• (c) The electron is negative. The nucleus is
  positive. So there is a force of electrostatic
  attraction between them

• Summary questions
• (a) gains, to, from
• (b) loses, from, to
• (a) attraction
• (b) attraction
• (c) repulsion

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Electric current

• An electric current is equal to the rate of flow
  of electrical charge through a conductor.
• In metallic conductors (e.g. copper wire)
  electrons carry negative charge from the negative
  side of a power supply, around a circuit and back
  into the positive side.

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Discharging an object
negatively charged object

• A charged body can be discharged by connecting it
  to the ground with a conductor.
• Charge then flows through the conductor.
• This process is also called earthing.
• A person is usually a good enough conductor to
  enable an object to be discharged.

object discharged
negative charge flows to earth
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Sparks

• The greater the charge on an isolated body the
  greater the potential difference (voltage)
  between the body and earth.
• If the potential difference becomes high enough a
  spark may jump across the gap between the body
  and any earthed conductor which is brought near
  it.

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Choose appropriate words to fill in the gaps
below The greater the _______ on an object the
greater is the potential difference (or
_________) between the object and the earth. An
electric current will flow when a ________ is
used to link a charged object and the ______.
This is called earthing and results in the
object becoming ___________. Electric current is
the rate of _____ of electric charge. If the
potential difference is high enough a ____ may
occur between the object and the earth. _______
is an example of this.
charge
voltage
conductor
earth
discharged
flow
spark
lightning
WORD SELECTION
discharged
voltage
conductor
spark
earth
lightning
charge
flow
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Charge on the moveNotes questions from pages 162
163

1. What does electric current consist of?
2. Explain, in terms of electrons, how a metal
   conducts electricity.
3. Copy and answer question (a) on page 162.
4. Explain how a conductor can become (a) charged
   and (b) discharged.
5. Copy and answer questions (b) and (c) on pages
   162 and 163.
6. When do sparks occur?
7. Copy the Key Points on page 163.
8. Answer the summary questions on page 163.

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Charge on the move ANSWERS

• In text questions
• The positive end
• electrons transferred to the can pass through it
  to the ground.
• It gains electrons

• Summary questions
• 1. (a) The rate of flow of charge
• (b) Electrons that move about freely
• (c) Negatively charged
• 2. (a) Any charge supplied to it flows to Earth.
• (b) Charge leaks off the dome form the tip of
  the pin into the air.

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Uses of static electricity 1. Photocopier
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2. Smoke precipitator
An electrostatic precipitator is used to prevent
the dust and ash produced by coal fired power
stations from entering the atmosphere. The ash
and dust becomes charged as it passes through the
charged grid of wires. The ash and dust is then
attracted to the oppositely charged metal
plates. When the plates are shaken the
accumulated ash and dust falls down to be
collected and removed.
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3. Paint spraying
The spray nozzle is connected is connected to the
positive terminal of an electrostatic
generator. As the paint droplets leave they repel
each other and spread out to form a fine cloud of
paint. The metal panel to be painted is connected
to the negative terminal. The negatively charged
metal panel attracts the positively charged paint.
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Hazards of static electricity

• The main danger of static electricity is in
  situations where a spark can cause a fire or an
  explosion.
• The Buncefield oil depot explosion (opposite) in
  December 2005 was thought to have been caused by
  a spark.

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Pipe problems

• When oil or petrol is pumped along pipes a static
  charge can build up on the pipe which could
  result in a spark.
• This could cause an explosion when the fuel
  vapour reacts with oxygen in the air.

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Antistatic floors

• In operating theatres it is important that the
  doctors to do not become statically charged when
  walking around.
• This is because some of the anaesthetic gases
  used are explosive.
• Antistatic material is used for the floor surface
  so that any charge is conducted to earth.

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Uses and dangers of static electricityNotes
questions from pages 164 165

1. Explain how static electricity is used in (a) a
   paint sprayer and (b) an electrostatic
   precipitator (draw a diagram)
2. Copy and answer questions (a), (b) and (c) on
   page 164.
3. Explain three hazards of static electricity.
4. Copy and answer questions (d) and (e) on page
   165.
5. Copy the Key Points on page 165.
6. Answer the summary questions on page 165.

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Uses and dangers of static electricity ANSWERS

• In text questions
• So that droplets are charged as they leave the
  spray nozzle and attracted to the panel.
• Most of the particles would pass straight through
  it.
• The powder transfers charge onto the paper from
  the photocopier drum. The charge stays on the
  paper sometimes.
• So that it conducts charge away from the pump
  nozzle to Earth.
• So their clothing doesnt become charged and
  produce sparks.

• Summary questions
• (a) repelled, gain
• (b) lose, attracted
• 2. (a) To conduct any charge on the pipe nozzle
  to the ground, so it cant cause sparks which
  would ignite the fuel.
• (b) To conduct any charge to the ground so
  it cant cause sparks, which would cause gases
  used in the theatre to explode.

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Virtual Physics Laboratory SimulationsNOTE
Links work only in school

• Electrometer.exe Electroscope
• Electrostatic Induction.exe Does not work in
  all cases
• Electrostatic Pendulum.exe - Shows how current
  is produced by charge flow
• Van der Graaf.exe

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Online Simulations

• Balloons Static Electricity - PhET - Why does a
  balloon stick to your sweater? Rub a balloon on a
  sweater, then let go of the balloon and it flies
  over and sticks to the sweater. View the charges
  in the sweater, balloons, and the wall.
• Electric Magnetic Forces - 'Whys Guy' Video
  Clip (330mins) - Shows Charged Balloon Effect
  of a magnet on a TV screen.
• John Travoltage - PhET - Make sparks fly with
  John Travoltage. Wiggle Johnnie's foot and he
  picks up charges from the carpet. Bring his hand
  close to the door knob and get rid of the excess
  charge.

• Fuel Ignition While Refuelling A Car - Word
  document with embedded video clip
• Charged Rod Pith Ball - Iona
• Electric Force Tutorial - Science Trek
• How photocopying works - University of Delaware
• BBC KS3 Bitesize Revision
• Electrical Charge
• BBC AQA GCSE Bitesize Revision
• Attraction Repulsion
• Uses of static electricity
• Charge, current, energy and time relationships

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Static issues Notes questions from pages 166
167

1. Answer questions 1, 2 and 3 on pages 166 and 167.

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Static issues ANSWERS

• 1. (a) All charged objects either attract or
  repel each other. You only need two types to
  fit the force rule.
• (b) All the extra electrons carrying the
  negative charge would make up for the deficit of
  electrons in the positive charge.
• 2. Electrons transfer to the electroscope so the
  leaf and the stem both become positively charged.
  The leaf therefore goes up. The charge stays on
  the electroscope so the leaf stays up.
• 3. They would not be deflected by the correct
  amount.

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How Science Works ANSWERS

1. To ensure that the results are valid, i.e. it is
   a type of control for different people carrying
   out the testing.
2. When lightning was striking.
3. The air temperature.
4. As many people as possible (e.g. a minimum of 50
   as there is likely to be a wide range of
   temperatures.)
5. Microseconds are used to time the response of the
   lightning conductor.
6. The lightning conductor may have been damaged.
7. It could be done by both. However, a potential
   buyer would want to be assured of its reliability
   and therefore an independent company would be
   better. The testing will probably be monitored by
   an independent company.