SP12? physics

• Materials can be magnetised to become permanent or temporary magnents
• Magnetic materials include
• 1.COBALT
• 2.STEEL
• 3.IRON
• 4.NICKEL
• A permanent magnet has poles which are S and N all of the time, they are made from steel or magnadur
• A temporary magnet can be magnetised by bringing a permanent magnet near to it, when the magnet is removed the magnetism is removed.
• Like magnetic poles repel and unlike poles attract eachother
• The magnetic field is strongest at the poles in a bar magnet! shown in the diagram

Uniform field 

• The field is constant, this is shown by parrallel equally spaced lines

plotting compasses

• Is used to plot the shape and direction of magnetic lines of a force.
• You can do this by laying a bar magnet on a piece of paper then put the plotting compass by one pole of the magnet, draw a dot by the needle away from the magnet
• Move the plotting compass so that the other point is by the dot that has just been drawn, contine to do this until all the way around the magnet is mapped
• The Earths magnetic field has the same pattern as that of a bar magnet and can be plotted using a plotting compass.
• The behaviour of compasses is evidence that the earth has a magnetic field.

An electric current will create a magnetic field, the field is made up of concentric circles perpendicular to the wire. The shape, direction and strength of the field depend on a number of factors.Changing the direction of the current changes the direction of the magnetic field. The larger the current through the stronger the magnetic field.

remember to use the right hand right thumb and finger rule, thumb=current, curling of fingers=direction of the field

The solenoid 

The magnetic field lines of the individual coils in a solenoid add up to give a very strong, uniform field along the centre of a solenoid.However the field lines cancel to give a weaker field outside of the solenoid

A current-carrying conductor, placed near a magnet will experience a force due to the interaction of their magnetic fields.

The motor effect

An electric current flowing through a wire has a magnetic field. If you put the wire in to a field of another magnet then it will experience a force this is called the Motor effect.

The maximum force on the wire occurs when the current is at right angles to the lines of the magnetic field.

Fleming's left hand rule 

• There is no force if the CURRENT is PARRALLEL to the FIELD LINES.
• If the direction of either the CURRENT of the MAGNETIC FIELD is reversed the direction of the FORCE is REVERSED
• The size of the FORCE can be INCREASED by INCREASING the STRENGTH of the MAGNETIC FIELD, or INCREASING the SIZE of the CURRENT.