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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6- 1 Magnetism and Electromagnetism Edexcel IGCSE Physics pages 179 to 186 September 19 th 2012 Content applying to Triple Science only is shown in red type on the next slide and is indicated on subsequent slides by ‘TRIPLE ONLY

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

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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism. Content applying to Triple Science only is shown in red type on the next slide and is indicated on subsequent slides by ‘ TRIPLE ONLY ’. Edexcel IGCSE Physics pages 179 to 186. September 19 th 2012. - PowerPoint PPT Presentation

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

EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1

Magnetism and Electromagnetism

Edexcel IGCSE Physics pages 179 to 186

September 19th 2012

Content applying to Triple Science only is shown in red type on the next slide and is indicated on

subsequent slides by ‘TRIPLE ONLY’

Page 2: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Edexcel Specification

Section 6: Magnetism and electromagnetism b) Magnetismunderstand that magnets repel and attract other magnets and attract magnetic substancesdescribe the properties of magnetically hard and soft materialsunderstand the term ‘magnetic field line’understand that magnetism is induced in some materials when they are placed in a magnetic fielddescribe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnetsdescribe 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

Page 3: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnets and magnetic materials

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.

stainless steel

cobaltnickeliron

TRIPLE ONLY

Page 4: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Hard and soft magnetic materialsPermanent 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.

TRIPLE ONLY

Page 5: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetic poles

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)

Iron filing are attracted mostly to the poles of

a magnet

TRIPLE ONLY

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

Why poles are called north and southA 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 Earth’s magnetic field.

A compass is an application of this effect.

north

TRIPLE ONLY

Page 7: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

The law of magnets

Like poles repel unlike poles attract

TRIPLE ONLY

Page 8: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetic fieldsA 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.

Page 9: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetic field around a bar magnetmagnetic field line Arrows on the field

lines show the direction of the force on a free to move north pole

The stronger the magnetic field the denser the magnetic field lines.

Page 10: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetic fields between two bar magnets

Page 11: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Producing a uniform magnetic fieldA 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.

Page 12: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

The Earth’s magnetic fieldThe earth’s 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

Page 13: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Induced magnetismMagnetism 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 Earth’s crust such as lodestone have been magnetised in this way by the Earth’s magnetic field.

TRIPLE ONLY

N S

iron bar

Page 14: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

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.

softrepel fieldsteel directionpole pairs

WORD SELECTION:

TRIPLE ONLY

soft

repel

field

steel

direction

pole

pairs

Page 15: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Electromagnetism

In 1820 Hans Ørsted noticed that a wire carrying an electric current caused a compass needle to deflect.

No current, compass

points to north

Current, compass deflected

Page 16: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetic field patterns around wires1. 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.

Page 17: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

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.

Page 18: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Complete the diagrams below:

TRIPLE ONLY

Electric current out of the page

Electric current into the page

Add field arrows

Add field arrows

Add current direction

Add current direction

Page 19: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

2. Flat circular coil

TRIPLE ONLY

Plan view

Page 20: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

3. Solenoid

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:

1. the electric current

2. the number of turns in the coil

TRIPLE ONLY

N S

Page 21: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

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

Page 22: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Complete the diagrams below:

TRIPLE ONLY

1. Locate north

4. Add coils

3. Add current direction2. Locate south

N

N

S

N

Page 23: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Electromagnets

An electromagnet consists of a current carrying coil wrapped around an iron core.

TRIPLE ONLY

Page 24: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Uses of electromagnets1. 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.

TRIPLE ONLY

Page 25: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

2. The electric bellWhen 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.

TRIPLE ONLY

gong

hammer

electromagnet

push switch spring

contact switch

soft iron armature

Page 26: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Label the diagram of the electric bell below:TRIPLE ONLY

1

2

3

4

5

6

Contact switch7

8

Page 27: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

3. The relay switchA 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.

TRIPLE ONLY

switch A

springy contact switch B

iron armature

hinge

electromagnet

to high voltage circuit

Page 28: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

A

B

4. Circuit breakerCurrent 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.

The reset button can be pushed to bring the contact back to its original position to reconnect the circuit

1

2

Domestic circuit

breakers

TRIPLE ONLY

Page 29: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

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.

solenoid strengthiron softturns currentelectromagnet

WORD SELECTION:

TRIPLE ONLY

solenoid

strength

iron

soft

turns

current

electromagnet

Page 30: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Online SimulationsBar 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 - NTNURelay demonstration - Freezeway.com Electric Bell demonstration - Freezeway.comBBC KS3 Bitesize Revision: Bar Magnets Magnetic Fields Electromagnets Using Electromagnets - includes an applet showing how an electric bell works

Page 31: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetism and Electromagnetism Notes questions from pages 179 to 186

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.

TRIPLE ONLY

Page 32: EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 6-1 Magnetism and Electromagnetism

Magnetism and Electromagnetism Notes questions from pages 179 to 186

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)

DOUBLE SCIENCE ONLY