Magnetism Test (Physics #2)

Magnetism

• Magnet: an object that can exert a pull or force on a piece of iron.
• Magnetic energy is composed of lines of force. Each magnet has two poles: north and south. The lines of force go out of the north and into the south.
• These lines of force make a magnetic field.
• A Permanent Magnet: a material whose magnetic domain (the small region within a magnetic substance) are aligned in the same direction and retain their alignment for long periods of time.
• A compass placed along a line of force indicates the direction of a force. The north pole of the needle will point in the direction of the magnetic line of force.
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Magnetism Continued

• When domains are randomly arranged, they are not magnetic. When domains are arranged with all poles facing the same direction, they are strongly magnetic!
• Magnetic Substances: Iron, Nickel, Cobalt, Gadolinium
• Types of Magnets:
• Permanent Magnets: magnetic materials whose magnetic domains are aligned in the same direction and retain this alignment for long periods of time
• Temporary Magnets: objects that become magnetic only as long as they are within a magnetic field
• Electromagnets: objects (coils of wire) that become magnetic when an electric current is applied
• The geomagnetic poles of the Earth are the magnetic poles to which magnets are attracted. The North pole of a compass points to the magnetic South pole of the Earth (geomagnetic north pole.)
• The geographic poles indicate the center of the Earth's rotation.
• Examples of Types of Magnets:
• Permanent Magnets: fridge magnet, speaker magnet, compass, magnetic door holder
• Temporary Magnets: nail attached to a magnet, paperclip
• Electromagnets: car lifter, speaker magnet, energized coil of wire, magnetic door holder

Destroying a Permanent Magnet

• How can you damage or destroy a permanent magnet?
• Disrupting the direction of magnetic domains will reduce or destroy the magnetic field.
• Storing multiple magnets together with magnetic fields that repel (similar poles together)
• Striking or dropping the magnet
• Heating the magnet
• Keep in mind: Cutting the magnet will only create smaller magnets!

Electromagnetism

• Electromagnetism is the magnetic field caused by current electricity.
• Discovered by Hans Oersted in 1820s
• The field around a current-carrying wire is circular. The direction of the current determines the direction of the magnetic field.
• Conventional current flows from positive to negative
• A compass needle will point in the direction of the magnetic field lines
• **Remember: downright. If the current goes right, the arrows of the circular magnetic fields point down.
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Electromagnetism Continued

• Compasses under and over straight wires. Use the Right-Hand Rule...
• Point your pencil as shown in the drawing of the wire. The tip should point negative.
• Point the thumb of your right hand in the direction of conventional current flow: so it faces the negative end.
• Determine whether it is under or over. Move your fingers accordingly. The direction of your fingers will indicate the direction of the magnetic field.
• Magnetic fields around a current coming towards you or moving away from you
• If the wire has a small dot, it is coming towards you. If the wire has an x, it is moving away from you.
• X is clockwise. Dot is counter-clockwise. Or: point your thumb in the proper direction and see which way your fingers move.

The Wonderful World of Solenoids

• Solenoid: a wire coiled around a piece of metal which develops a magnetic field when current electricity is applied.
• To Make a Stronger Solenoid:
• More wire wraps
• Stronger current/voltage
• Metal core
• Quality of the conductor
• It consists of a piece of metal, a coil of wire, the direction of conventional flow, North and South poles, and + and - symbols.
• Use the Right-Hand Rule! Wrap your fingers around the pencil in the direction of current flow and your thumb will point north.
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The Electric Motor

• An electric motor is a device that converts electrical energy into mechanical energy. A generator does the reverse.
• How does it work?
• Motors use a permanent magnet with fixed north and south poles and a coil of wire.
• Current alternates direction in the coil of wire, causing the electromagnetic poles to alternate.
• The alternating attraction between the shifting poles on the coil and the poles on the magnet causes movement of the coil or the magnet.
• Parts of an Electric Motor:
• The coil wrapped around Armature - where current flows
• Brushes - electrical contacts
• Commutator - split ring
• Stator - permanent magnet
• How to make a stronger motor:
• Increase the number of wraps in the coil.
• Use more powerful permanent magnets.
• Increase the flow of current electricity.