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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism Edexcel IGCSE Physics pages 179 to 186 Content applying to Triple Science only is shown in ... – PowerPoint PPT presentation

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Title: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism


1
EDEXCEL IGCSE / CERTIFICATE IN PHYSICS
6-1 Magnetism and Electromagnetism
  • Edexcel IGCSE Physics pages 179 to 186

Content applying to Triple Science only is shown
in red type on the next slide and is indicated on
subsequent slides by TRIPLE ONLY
September 19th 2012
2
Edexcel Specification
  • Section 6 Magnetism and electromagnetism
  • b) Magnetism
  • understand that magnets repel and attract other
    magnets and attract magnetic substances
  • describe the properties of magnetically hard and
    soft materials
  • understand the term magnetic field line
  • understand that magnetism is induced in some
    materials when they are placed in a magnetic
    field
  • describe experiments to investigate the magnetic
    field pattern for a permanent bar magnet and that
    between two bar magnets
  • describe how to use two permanent magnets to
    produce a uniform magnetic field pattern.
  • c) Electromagnetism
  • understand that an electric current in a
    conductor produces a magnetic field round it
  • describe the construction of electromagnets
  • sketch and recognise magnetic field patterns for
    a straight wire, a flat circular coil and a
    solenoid when each is carrying a current

Red type Triple Science Only
3
Magnets and magnetic materials
TRIPLE ONLY
  • Magnets attract objects made of magnetic
    materials
  • Magnetic materials include the elements iron,
    nickel, cobalt, alloys containing some of these
    such as steel and some of their compounds.

4
Hard and soft magnetic materials
TRIPLE ONLY
  • Permanent magnets are made of magnetically HARD
    materials such as steel. These materials retain
    their magnetisation once magnetised.

Magnetically SOFT materials, such as iron, lose
their magnetisation easily. They suitable for
temporary magnets such as electromagnets.
5
Magnetic poles
TRIPLE ONLY
  • Magnetic poles are the parts of a magnet that
    exert the greatest force.
  • Magnetic poles occur in pairs usually called
    north (N) and south (S)

6
Why poles are called north and south
TRIPLE ONLY
  • A magnet suspended so that it can rotate freely
    horizontally will eventually settle down with one
    pole facing north and the other south.
  • This is pole is therefore called the north
    seeking pole, usually shortened to just north
    pole.
  • The magnet has been orientated by the Earths
    magnetic field.
  • A compass is an application of this effect.

7
The law of magnets
TRIPLE ONLY
  • Like poles repel unlike poles attract

8
Magnetic fields
  • A magnetic field is a volume of space where
    magnetic force is exerted.
  • All magnets are surrounded by magnetic fields.
  • The shape of a magnetic field can be shown by
    iron filings or plotting compasses.

9
Magnetic field around a bar magnet
10
Magnetic fields between two bar magnets
11
Producing a uniform magnetic field
  • A uniform magnetic field exerts a constant force
    over a region.
  • Such a field will consist of parallel equally
    spaced magnetic field lines.
  • This type of field can almost be found between a
    north and south magnetic pole.

12
The Earths magnetic field
  • The earths magnetic field is similar in shape to
    that around a bar magnet.
  • It is thought to be caused by electric currents
    flowing through the molten outer core of the
    Earth.
  • At the present the field pattern is like that
    with a magnetic SOUTH pole situated somewhere
    below northern Greenland

13
Induced magnetism
TRIPLE ONLY
  • Magnetism can be induced in a magnetic material
    if it is placed within a magnetic field.
  • If the material is magnetically hard it will
    retain its magnetism once removed from the field.
  • Certain rocks in the Earths crust such as
    lodestone have been magnetised in this way by the
    Earths magnetic field.

iron bar
14
TRIPLE ONLY
Choose appropriate words to fill in the gaps
below Magnetic materials are either hard or
______. Hard magnetic materials such as ______
retain their magnetisation once magnetised. A
magnetic _____ is a region where the magnetic
force is greatest. Magnetic poles always occur in
______. Like poles _______, unlike attract. A
magnetic ______ is a region where magnetic force
is exerted. The ________ of the magnetic field
around a bar magnet is from north to south.
soft
steel
pole
pairs
repel
field
direction
WORD SELECTION
soft
repel
field
steel
direction
pole
pairs
15
Electromagnetism
  • In 1820 Hans Ørsted noticed that a wire carrying
    an electric current caused a compass needle to
    deflect.

16
Magnetic field patterns around wires 1. Straight
wire
TRIPLE ONLY
The magnetic field consists of concentric circles
centred on the wire. The magnetic field is
strongest near the wire. This is shown by the
field lines being closest together near to the
wire. The strength of the field increases if the
electric current is increased.
17
The right-hand grip rule (for fields)
TRIPLE ONLY
Grip the wire with the RIGHT hand. The thumb is
placed in the direction of the electric
current. The fingers show the direction of the
circular magnetic field.
18
Complete the diagrams below
TRIPLE ONLY
Add field arrows
Add field arrows
Add current direction
Add current direction
Electric current out of the page
Electric current into the page
19
2. Flat circular coil
TRIPLE ONLY
20
3. Solenoid
TRIPLE ONLY
  • A solenoid is a coil of wire carrying an electric
    current.
  • The magnetic field is similar in shape to that
    around a bar magnet.
  • The strength of the field increases with
  • the electric current
  • the number of turns in the coil

21
The right-hand grip rule (for poles)
TRIPLE ONLY
Grip the coil with the RIGHT hand. The fingers
are placed in the direction that the eclectic
current flows around the coil. The thumb points
towards the north pole end of the coil.
N
S
22
Complete the diagrams below
TRIPLE ONLY
1. Locate north
3. Add current direction
2. Locate south
S
N
N
4. Add coils
23
Electromagnets
TRIPLE ONLY
  • An electromagnet consists of a current carrying
    coil wrapped around an iron core.

24
Uses of electromagnets
TRIPLE ONLY
  • 1. Scrap yard crane
  • The iron core of the electromagnet is a SOFT
    magnetic material.
  • When current flows the iron becomes strongly
    magnetised and so picks up the scrap iron and
    steel.
  • When the current is turned off the iron loses its
    magnetisation and so releases the scrap.

25
2. The electric bell
TRIPLE ONLY
  • When the push switch is closed current flows
    around the circuit turning on the electromagnet.
  • The soft iron armature is pulled towards the
    electromagnet and the hammer hits the gong.
  • This causes the contact switch to open cutting
    off the electric current.
  • The spring now pulls the armature back again
    closing the contact switch.
  • Current now flows again and the hammer hits the
    gong again.

push switch
spring
electromagnet
contact switch
soft iron armature
hammer
gong
26
Label the diagram of the electric bell below
TRIPLE ONLY
Contact switch
27
3. The relay switch
TRIPLE ONLY
switch A
  • A relay switch is a way of using a low voltage
    circuit to switch remotely a high voltage (and
    possibly dangerous) circuit.
  • When switch A is closed, the small current
    provided by the cell causes the electromagnet to
    become magnetised..
  • The iron armature is then attracted to the
    electromagnet causing the springy contact switch
    B to close in the high voltage circuit.

iron armature
electromagnet
hinge
springy contact switch B
to high voltage circuit
28
4. Circuit breaker
TRIPLE ONLY
  • Current normally flows between terminals A and B
    through the contact and the electromagnet.
  • When the current in a circuit increases, the
    strength of the electromagnet will also increase.
    This will pull the soft iron armature towards the
    electromagnet.
  • As a result, spring 1 pulls apart the contact and
    disconnecting the circuit immediately, and
    stopping current flow.

2
1
The reset button can be pushed to bring the
contact back to its original position to
reconnect the circuit
29
TRIPLE ONLY
Choose appropriate words to fill in the gaps
below A wire carrying an electric ______
produces a magnetic field. This field increases
in ________ if the current is increased. A
________ is a coil of wire carrying an electric
current. The field produced increases in strength
if the number of _____ in the coil is increased
or if _____ is placed inside the coil. An
____________ consists of a coil of a solenoid
wrapped around an iron core. Iron is a ______
magnetic material that loses its magnetisation
once the current in the coil is switched off.
current
strength
solenoid
turns
iron
electromagnet
soft
WORD SELECTION
solenoid
strength
iron
soft
turns
current
electromagnet
30
Online Simulations
  • Bar magnet field - Fendt
  • Faraday Electromagnetic Lab - PhET - Play with a
    bar magnet and coils to learn about Faraday's
    law. Move a bar magnet near one or two coils to
    make a light bulb glow. View the magnetic field
    lines. A meter shows the direction and magnitude
    of the current. View the magnetic field lines or
    use a meter to show the direction and magnitude
    of the current. You can also play with
    electromagnets, generators and transformers!
  • Field around a straight conductor - Fendt
  • Magnetic field around a straight wire / coil /
    solenoid - NTNU
  • Relay demonstration - Freezeway.com
  • Electric Bell demonstration - Freezeway.com
  • BBC KS3 Bitesize Revision
  • Bar Magnets
  • Magnetic Fields
  • Electromagnets
  • Using Electromagnets - includes an applet showing
    how an electric bell works

31
Magnetism and Electromagnetism Notes questions
from pages 179 to 186
TRIPLE ONLY
  1. State what happens when different types of
    magnetic poles are placed near to each other.
    (see page 180)
  2. (a) What is the difference between magnetically
    soft and hard materials? (b) Give examples and
    uses of each type. (see page 180)
  3. (a) Draw the magnetic field patterns between and
    around magnets shown on page 181.(b) Explain what
    the magnetic field lines show about the magnetic
    fields.
  4. Explain how a uniform magnetic field can be
    produced. (see page 181)
  5. Draw the magnetic field patterns around and
    inside (a) a straight conducting wire (b) a
    flat coil (c) a solenoid. (see pages 182 and
    183)
  6. Draw a labelled diagram showing the construction
    of an electromagnet. (see page 183)
  7. Draw a diagram and explain the operation of an
    electric bell. (see page 183)
  8. Draw a diagram and explain the operation of a
    circuit breaker. (see page 184)
  9. Draw a diagram and explain the operation of a
    relay. (see page 185)
  10. Answer the questions on page 186.
  11. Verify that you can do all of the items listed in
    the end of chapter checklist on page 186.

32
Magnetism and Electromagnetism Notes questions
from pages 179 to 186
DOUBLE SCIENCE ONLY
  1. (a) Draw the magnetic field patterns between and
    around magnets shown on page 181.(b) Explain what
    the magnetic field lines show about the magnetic
    fields.
  2. Explain how a uniform magnetic field can be
    produced. (see page 181)
  3. Draw the magnetic field patterns around a
    straight conducting wire (see page 182)
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