MAGNETISM AND ITS MAGNETISM AND ITS USESUSES

CHAPTER 8CHAPTER 8

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The Greeks found a The Greeks found a mineral, they called mineral, they called (lode stone), now (lode stone), now called magnetite. It called magnetite. It had natural had natural magnetic propertiesmagnetic properties..

What explanations do What explanations do you think they gave you think they gave for the behavior of for the behavior of magnetite?magnetite?

SECTION 1:SECTION 1: MAGNETISMMAGNETISMA. Magnetism – the properties an A. Magnetism – the properties an

interactions of magnetsinteractions of magnets

1. Interaction between two magnets1. Interaction between two magnets

called magnetic force increases called magnetic force increases asas

magnets move closer together.magnets move closer together.

2. A magnetic field, which exerts the 2. A magnetic field, which exerts the

magnetic force, surrounds a magnetic force, surrounds a magnet, and is strongest magnet, and is strongest

closest closest to the magnet. to the magnet.

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B.B. Magnetic poles – the Magnetic poles – the regions of a magnet regions of a magnet where the magnetic force where the magnetic force exerted by the magnet is exerted by the magnet is strongeststrongest

1. All magnets have a 1. All magnets have a northnorth

pole and a south pole.pole and a south pole.

2. Like poles repel. 2. Like poles repel. Unlike poles attract. Unlike poles attract.

The magnetic field The magnetic field lines around lines around horseshoe and disk horseshoe and disk magnets are magnets are closest together at closest together at the magnet’s poles.the magnet’s poles.

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SLIDE 4SLIDE 4Magnets can attract or Magnets can attract or repel each other.repel each other.

Unlike poles attract. When Unlike poles attract. When unlike poles are brought unlike poles are brought together, their magnetic together, their magnetic field lines seem to field lines seem to connect with each other.connect with each other.

Like poles repel. When Like poles repel. When like poles are brought like poles are brought together, their magnetic together, their magnetic field lines seem to push field lines seem to push away from each other.away from each other.

SLIDE 5SLIDE 5C.C. Magnetic materials – iron, cobalt, and Magnetic materials – iron, cobalt, and nickelnickel1. The magnetic field created by each1. The magnetic field created by each atom exerted a force on nearby atoms.atom exerted a force on nearby atoms.2. Magnetic domains – groups of atoms2. Magnetic domains – groups of atoms

with aligned magnetic poles.with aligned magnetic poles. a. In a magnet, the like poles of all a. In a magnet, the like poles of all the domains point in the same the domains point in the same direction.direction. b. Permanent magnets are made by b. Permanent magnets are made by placing a magnetic material in a placing a magnetic material in a strong magnetic field, forcing a strong magnetic field, forcing a

large large number of magnetic number of magnetic domains to line domains to line up. up.

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3.3. Earth has magneticEarth has magnetic

poles.poles.

a.a. A compass A compass needle is aneedle is a

small bar magnet small bar magnet that can freely that can freely rotate.rotate.

b. A compass b. A compass needle always needle always points north.points north.

A normal iron nail is made up of billions of domains that are A normal iron nail is made up of billions of domains that are arranged randomly.arranged randomly.

The domains will align themselves along the magnetic field lines The domains will align themselves along the magnetic field lines of a nearby magnetof a nearby magnet..

Each piece of a broken magnet still has a north and a south pole.Each piece of a broken magnet still has a north and a south pole.

SECTION 2: SECTION 2: ELECTRICITY & ELECTRICITY & MAGNETISMMAGNETISM

A.A. Moving charges and magnetic fields.Moving charges and magnetic fields.1. Moving charges, like those in an electric current, 1. Moving charges, like those in an electric current,

produce magnetic fields. produce magnetic fields.a. The magnetic field around a current-carrying a. The magnetic field around a current-carrying wire forms a circular pattern about the wire. wire forms a circular pattern about the wire.b. The direction of the field depends on the b. The direction of the field depends on the direction of the current. direction of the current.c. The strength of the magnetic field depends c. The strength of the magnetic field depends

on on the amount of current flowing in the wire the amount of current flowing in the wire

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B. Electromagnet – a temporary magnet made B. Electromagnet – a temporary magnet made by placing a piece of iron inside a current-by placing a piece of iron inside a current-carrying coil of wire.carrying coil of wire.1. Magnetic field is present only when 1. Magnetic field is present only when

current is flowing in the wire.current is flowing in the wire.2. Increase strength of the magnetic field 2. Increase strength of the magnetic field

by adding more turns to the wire coil orby adding more turns to the wire coil orincreasing the current passing through increasing the current passing through the wire.the wire.

3.3. Magnetic properties of electromagnets can Magnetic properties of electromagnets can be controlled by changing the electric be controlled by changing the electric current flowing through the wire.current flowing through the wire.

4. Converts electrical energy into mechanical 4. Converts electrical energy into mechanical energy to do workenergy to do work..

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A. Magnetic field lines circle around a loop of current-carrying wire.

B. When many loop of current-carrying wire are formed into a coil, the magnetic field is increased inside the coil. The coil has a north pole and a south pole.

C. An iron core inserted into the coil becomes a magnet.

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The electromagnet in a The electromagnet in a speaker turns speaker turns electrical energy into electrical energy into mechanical energy to mechanical energy to produce sound.produce sound.

SLIDE 4SLIDE 4A.A. When current flows When current flows

through the coil, an through the coil, an electromagnet is formed electromagnet is formed that is attracted to and that is attracted to and repelled by the poles of repelled by the poles of the permanent magnet.the permanent magnet.

B.B. The magnetic forces on The magnetic forces on the coil cause it to rotate, the coil cause it to rotate, aligning it with the field of aligning it with the field of the permanent magnet.the permanent magnet.

C. Galvanometer – a device that uses an C. Galvanometer – a device that uses an electromagnetic to measure electric current.electromagnetic to measure electric current.

SLIDE 5SLIDE 5D.D. Electric motor – a device that changes electrical energy into Electric motor – a device that changes electrical energy into mechanical energy.mechanical energy.1. Contains an electromagnet that is free to 1. Contains an electromagnet that is free to

rotate between the poles of a permanent, rotate between the poles of a permanent, fixed magnet. The coil in the electromagnet is fixed magnet. The coil in the electromagnet is connected to a source of electric current.connected to a source of electric current.

2. When a current flows through the electromagnet, a2. When a current flows through the electromagnet, amagnetic field is produced in the coil.magnetic field is produced in the coil.

3. Changing the direction of the current causes the coil in an electric 3. Changing the direction of the current causes the coil in an electric motor to motor to keep rotating.keep rotating.4. Rotation speed of electric motors can be controlled.4. Rotation speed of electric motors can be controlled.

a. Vary the amount of current flowing through the coil.a. Vary the amount of current flowing through the coil.b. When more current flows through the coil, the electromagnet’s b. When more current flows through the coil, the electromagnet’s magnetic field becomes stronger, the magnetic force between turns faster.magnetic field becomes stronger, the magnetic force between turns faster.

A. A battery causes an electric current to A. A battery causes an electric current to flow through the coil of the electromagnet.flow through the coil of the electromagnet.

B. Unlike poles of the two magnets attract each other, and the like B. Unlike poles of the two magnets attract each other, and the like poles repel. This causes the coil to rotate until the opposite poles are poles repel. This causes the coil to rotate until the opposite poles are next to each other.next to each other.

C. If the current in the coil is switched, the direction of the coil’s C. If the current in the coil is switched, the direction of the coil’s magnetic field also switches. The north and south poles of the magnet magnetic field also switches. The north and south poles of the magnet trade places.trade places.

D. The coil is repelled by and attracted once again to the poles of the D. The coil is repelled by and attracted once again to the poles of the permanent magnet. The coil rotates until it is again aligned with the permanent magnet. The coil rotates until it is again aligned with the permanent magnet’s field.permanent magnet’s field.

SECTION 3:SECTION 3: PRODUCING ELECTRIC CURRENTPRODUCING ELECTRIC CURRENTA.A. From mechanical to electrical energyFrom mechanical to electrical energy

1. Electromagnetic induction – the 1. Electromagnetic induction – the production of an electric current by production of an electric current by moving a lop of wire through amoving a lop of wire through a magnetic field or moving a magnet magnetic field or moving a magnet through a wire loopthrough a wire loop

2. Generator – a device that produces 2. Generator – a device that produces electric current by rotating a coil of electric current by rotating a coil of wire in a magnetic fieldwire in a magnetic field a. The wire coil is wrapped around an irona. The wire coil is wrapped around an iron

core and placed between the poles of acore and placed between the poles of apermanent magnet.permanent magnet.

b. Coil is rotated by an outside source of b. Coil is rotated by an outside source of mechanical mechanical energy. energy.

c. As the coil turns within the magnetic field of the c. As the coil turns within the magnetic field of the permanent magnet, an electric current flows permanent magnet, an electric current flows

through through the coil. the coil. d. Direction of the current in the coil in a generator d. Direction of the current in the coil in a generator changes twice with each revolution. changes twice with each revolution.

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The electromagnet The electromagnet in a generator is in a generator is rotated by some rotated by some outside source of outside source of mechanical energy. mechanical energy. In this setup, a In this setup, a student can rotate a student can rotate a crank to turn the crank to turn the electromagnet.electromagnet.

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The direction that The direction that current flows in a current flows in a wire coil depends on wire coil depends on how the wire coil is how the wire coil is aligned with the aligned with the permanent magnet.permanent magnet.

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3.3. Generating electricityGenerating electricity

a. Electricity used in the home comes from a a. Electricity used in the home comes from a power plant with huge generators.power plant with huge generators.

b. Coils of electromagnets in the generatorsb. Coils of electromagnets in the generators

usually connected to a turbine – a largeusually connected to a turbine – a large

wheel that rotates when pushed by wheel that rotates when pushed by water, wind, or steam.water, wind, or steam.