Magnetism

Magnetism

1. HOW DO OBJECTS BECOME CHARGED

   • Atoms have the same number of protons as electrons, which means the overall charge is zero
     • When two materials are rubbed together, the electrons are passed between the materials.
       • One of the materials gains more electrons than normal and the other ends up with fewer electrons
         • This means that one has an overall negative charge and the other has an overall positive charge

2. Three magnetic elements - Nickel, Cobalt and Iron

3. THREE METHODS OF MAGNETISING METALS

   • 1. Take a magnetic material and stroke a permanent magnet along it in the same direction each time
   • 3. Heat up a magnetic material. Put it in a strong electromagnetic field. The E.F will line up all the magnetic domain.
   • 2. Heat up a magnetic material. Line it up in the Earths magnetic field. Tap it gently with a hammer. This will line up the magnetic domains

4. MAGNETIC FIELD LINES

   • Always go N to S
   • Describe the same amount of force
   • Never touch
   • Are more dense at the poles where the field is the strongest

5. HARD AND SOFT MAGNETISM MATERIALS

   • Iron is a soft magnetic material and is useful for electromagnets where we want the magnetism to be removed quickly (eg scrapheap)
     • East to magnetise but lose magnetism easily
   • Steel is a hard magnetic material and is useful for making permanent magnets.
     • Does not lose magnetism easily

6. ELECTROMAGNETS

   • When a current flows through a wire, a magnetic field is created around the wire.
   • A solenoid can be made by wrapping a length of insulated wire into a coil and connecting it to a source of electricity
   • Electric Bells
     • 1. When the switch is closed and the circuit is completed, a current flows through the electromagnet
     • 2.The coil become magnetic and attracts the steel hammer, which hits the bell.
     • 3. Because the steel has moved, the circuit is broken, whih means that the steel hammer goes back as it is no longer attracted to the coil as it is not magnetised
     • 4. The circuit reconnets and the process repeats
   • The strength of the magnetic field can be increased by inserting an iron nail into the wire coil.
   • Relay
     • It is made up of a coil of wire wound on an iron core.
     • When a current is passed through the coil, the core becomes magnetised
     • The core then attracts the iron armature, which is pivoted, causing it to close the contacts
     • When the current is switched off, the armature loses its magnetism and the contacts are released

7. HOW TO FIND THE SHAPE OF A MAGNETIC FIELD LINE WITH A COMPASS

   • 1.Start with the compass near one end of the magnet and mark the needle position using two dots
     • 2. The compass is then moved so that the needle lines up with the dot that you have already drawn.
       • 3. You carry this on until all the dots are joined up