Magnetism

• The magnetic fields are the strongest at the poles of a magnet
• When two magnets are brought close together, they repel if their like poles are facing each other or attract if unlike poles face each other.
• Attraction and repulsion of two magnetic poles are non-contact forces
• Non-contact force is a force that does not involve physical contact between two objects.
• Permanent magnet produces its own magnetic field
• Induced magnet becomes a magnet when placed in a magnetic field
• Induced magnets always have a force of attraction
• If the permanent magnet is taken away from the induced magnet, it will lose its magnetism very quickly
• The strength of an electromagnet can be increased by increasing the current through the coil or using more turns on the coil
• A solenoid is a long wire wound into a spiral shape to create a strong magnetic field inside the coil
• When a current flows through a solenoid, it creates a magnetic field around the coil
• The four types of magnetic materials are iron, steel, cobalt and nickel. They can become permanent or induced magnets.
• A magnetic field is a region around a magnet where a force acts on another magnet or on a magnetic material.
• The strength of the magnetic field depends on the distance from the magnet. The closer the magnet, the stronger the magnetic field.
• The strength of a magnetic field depends on the size of current in a circuit.
• The magnetic field is the strongest closer to the wire, and decreases as you move away from the wire
• If the direction of current changes, the magnetic field direction also changes
• According to the right-hand grip rule, the thumb points in the direction of the conventional current, while the fingers point in the direction of the magnetic field.
• To increase the strength of the magnetic field produced by a solenoid, you can increase the size of current, increase the number of turns in the coil, or you can place an iron inside the solenoid.
• Solenoids with an iron core inside it is an electromagnet.
• Electromagnets are used in electric motors, generators, transformers, relays, and loudspeakers.
• Electromagnets can be turned on or off
• The motor effect is the force a wire with current will experience when placed between two magnets producing their own magnetic field.
• Force (N) = Magnetic flux density (T) × Current (A) × length (m)

  Applies to wires which are at right angles to magnetic fields.
• Force depends on magnetic flux density, current, and length
• Flemming's left hand rule states that the first finger points to the direction of the magnetic field (North to south), the second finger points to the direction of the conventional current (+ to -), and the thumb points to the direction of force.
• If the wire is parallel to the magnetic field between two magnets, it will experience no force.