Magnetism Basics

Magnetism

• Magnets attract or repel other magnets and magnetic materials. Like poles repel, and opposite poles attract.
• Non-magnetic materials are not attracted to magnets and cannot be magnetized (e.g., glass, plastic).
• Magnetic materials are attracted to magnets and can be magnetized (e.g., iron, steel, cobalt, nickel).
• Magnetism can be induced in magnetic materials by placing them in a magnetic field.
• Magnetically hard materials can be permanently magnetized (e.g., steel).
• Magnetically soft materials are only temporarily magnetized (e.g., soft iron).
• Magnetic field lines represent the magnetic force on a north pole at a given point. The direction of a magnetic field line shows the direction of the force. The closer the field lines are to each other, the stronger the force.
• Field lines from magnets point from north to south.
• Between opposite poles of magnets placed close together, the field is uniform, the field lines are parallel and evenly spaced.

Electromagnetism

• An electric current passing through a conductor produces a magnetic field around it.
• Electromagnets consist of a coil of wire wrapped around a magnetically soft core; they can be turned on and off.
• The right-hand grip rule determines the direction of the magnetic field produced by a current-carrying wire.
• The magnetic field created by a solenoid (a coil of wire) is similar to that of a bar magnet.
• The magnetic field created by a flat circular coil has a specific pattern.

DC Motors

• DC motors have a coil of wire in a magnetic field.
• Current flows through the wire, creating forces that cause the coil to turn.
• Increasing the current, using a stronger magnetic field, or increasing the number of turns on the coil increases the turning effect.
• A split-ring commutator reverses the current every half-turn, ensuring continuous rotation.

Loudspeakers

• Loudspeakers use a coil attached to a cone in a magnetic field.
• Alternating current causes the cone to move, producing sound.
• Changing the alternating current changes the frequency of the sound.

Electromagnetic Induction

• Movement between a conductor and a magnetic field induces a voltage.
• This effect, known as electromagnetic induction, can be used to generate electricity. Factors affecting the induced voltage and current are increased speed, strength of the magnetic field, or size of the loops of the conductor in the field.

Transformers

• Transformers use two coils wrapped around a soft iron core to change voltage.
• A step-up transformer increases voltage, while a step-down transformer decreases voltage.
• The ratio of the number of turns in the primary coil to the number of turns in the secondary coil determines the voltage ratio.
• Transformers are used to transmit electrical power efficiently over long distances.