Magnetic fields

Magnetic fields

1. What are they?

   • Magnetic fields are areas where a magnetic force acts
     • A MAGNETIC FIELD is a region where MAGNETIC MATERIALS and also WIRES CARRYING CURRENTS experience A FORCE acting on them

2. The magnetic field round a current-carrying wire

   • 1. When a current flows through a wire, a magnetic field is created around the wire
     • 2. The field is made up of CONCENTRIC CIRCLES with the wire in the centre
       • 3. FLEMING'S RIGHT HAND RULE

3. The magnetic field round a coil of wire

   • 1. The magnetic field INSIDE a coil of wire is STRONG AND UNIFORM
     • 2. OUTSIDE the coil, the magnetic field is just like the one round a BAR MAGNET
       • 3. You can increase the STRENGTH of the magnetic field around a coil of wire by adding a MAGNETICALLY 'SOFT' IRON CORE through the middle of the coil. It's then called an ELECTROMAGNET
         • 4. A MAGNETICALLY SOFT material MAGNETISES and DEMAGNETISES very easily. So, as soon as you TURN OFF the current through the coil of wire, the magnetic field DISAPPEARS- the iron doesn't stay magnetised
           • 5. This is what makes it USEFUL for something that needs to be able to SWITCH its magnetism ON and OFF
             • Electromagnets are useful as their magnetism can be turned off
               • An electromagnet must be CONSTANTLY SUPPLIED with current-as that's what produces the MAGNETIC FIELD. So if the current stops, it stops being magnetic. Magnets you can switch off at your whim can be really useful...
                 • Example
                   • Cranes used for lifting iron and steel
                     • 1.Magnets can be used to ATTRACT and PICK UP things made from MAGNETIC MATERIALS, such as iron and steel
                       • 2. Electromagnets are used in some cranes e.g. in scrap yards and steel works