Electromagnetism + magnets +motors

• Permanent magnets


  Produce their own magnetic field
• Induced magnets


  Magnetic materials that turn into a magnet when they're put into a magnetic field
• Permanent and induced magnets


  The force between them is always attractive
• When you take away the magnetic field, induced magnets quickly lose their magnetism (or most of it) and stop producing a magnetic field</b>
• Magnetism


  1. Permanent magnets

  2. Induced magnets
• Magnetic field lines go from north to south pole of a magnet
• The closer together the magnetic field lines, the stronger the magnetic field
• The magnetic field is strongest at the poles of a magnet
• A moving charge creates a magnetic field around the wire, made up of concentric circles perpendicular to the wire
• Changing the direction of the current changes the direction of the magnetic field
• The strength of the magnetic field produced changes with the current and the distance from the wire
• Solenoid


  A coil of wire that increases the strength of the magnetic field
• The magnetic field inside a solenoid is strong and uniform
• The ends of a solenoid act like the north and south poles of a bar magnet
• Putting an iron core in the centre of a solenoid increases the field strength even more
• Electromagnet


  A solenoid with an iron core, where the magnetic field can be turned on and off with an electric current
• Motor effect


  1. Current-carrying wire in a magnetic field experiences a force

  2. Force acts at right angles to the magnetic field and the direction of the current

  3. Force increases with magnetic field strength and current
• Fleming's left-hand rule


  Used to determine the direction of the force on a current-carrying conductor in a magnetic field
• Electric motor


  1. Current-carrying coil of wire in a magnetic field experiences forces that cause it to rotate

  2. Spring commutator keeps the rotation in the same direction

  3. Direction of rotation can be reversed by reversing the current or the magnetic field
• The speed of the motor can be increased by increasing the current, adding more turns to the coil, or increasing the magnetic flux density