magnets

• magnets produce...


  magnetic fields
• all magnets have a ... and ... pole

  north, south
• magnetic field


  the region around a magnet where the magnetic force is exerted on other magnets or magnetic materials
• magnetic materials


  Iron, steel, nickel and cobalt
• magnetic field lines


  lines that map out the invisible magnetic field around a magnet - they always go from north to south and show which way a force would act on north pole if it was put at that point in the field
• the closer together the lines, the ... the magnetic field is

  stronger
• the further away the lines, the ... the magnetic field is

  weaker
• the force between a magnet and a magnetic material is always...

  attractive, no matter the pole
• what happens if two poles of a magnet are put near each other?

  they will exert a force on each other - this force can be attractive (if they are unlike poles) or repulsive (if they are like poles)
• like poles


  same poles, two north poles or two south poles
• unlike poles


  different magnetic poles, a north pole and a south pole
• what do compasses show of a magnetic field?


  the direction
• how do compasses show the direction of magnetic fields?

  inside a compass is a tine bar magnet (the needle) - the north pole of this magnet is attracted to the south pole of any other magnet it is near, so the compass needle point in the direction of the magnetic field it is it
• magnetic field lines with a compass


  you can move a compass around a magnet and trace the needle's position on paper to create a sketch of what the magnetic field looks like
• which direction to compass needles point when not near a magnet and why?

  north - because the Earth generates its own magnetic field, which shows that the inside (core) of the Earth must be magnetic
• a bar magnet's magnetic field lines go from...

  north to south, no matter which direction the magnet is pointing
• magnets can be ... or ...

  permanent, induced
• permanent magnets


  objects that keep their magnetic properties for a long time and produce their own magnetic field
• induced magnets


  magnetic materials that become magnetised when placed into a magnetic field - when you remove the magnetic field, it quickly loses most of its magnetism
• the force between a permanent and an induced magnet is always...

  attractive
• a moving charge creates a...

  magnetic field
• what happens when current flows through a wire?

  a magnetic field is created around the wire - this field is made up of concentric circles perpendicular to the wire, with the wire in the centre
• what happens when you place a compass near a wire that is carrying a current?

  as you move the compass, it will trade the direction of the magnetic field
• what does changing the direction of a the current flowing through a wire do?

  it changes the direction of the magnetic field
• the right hand thumb rule

  using your right hand, point your thumb in the direction of current and curl your fingers. The direction of your fingers is the direction of the field
• the strength of the magnetic field produced by a wire with current flowing through it changes with...

  the current and the distance from the wire: the larger the current through the wire, or the closer to the wire you are, the stronger the field is
• electromagnets can be...


  switched on and off
• electromagnets


  a type of magnet whose magnetic field is produced by the flow of electric current.
• a solenoid is a coil of...

  wire
• how can you increase the strength of a magnetic field that a wire produces?

  by wrapping the wire into a coil called a solenoid
• solenoid


  a coil of wire that produces a magnetic field when carrying an electric current
• how does a solenoid increase the strength of a magnetic field?

  because the field lines around each loop of wire line up with each other, resulting in lots of field lines pointing in the same direction that are very close to each other and the closer together the field lines are, the stronger the field is
• the magnetic field inside a solenoid is...

  strong and uniform (it has the same strength and direction at every point in that region)
• outside the solenoid, the magnetic field is...

  just like the one around a bar magnet
• how does putting a block of iron in the centre of the coil increase the solenoid's field strength?

  because the iron core becomes an induced magnet whenever current is flowing
• a solenoid with an iron core is an...

  electromagnetic, meaning that its magnetic field can be turned on and off with an electric current
• how are electromagnets used in planes?

  they are used in some planes to attract and pick up things made from magnetic materials like iron and steel, e.g. in scrap yards - using an electromagnet means that the magnet can be switched on when you want to pick stuff up and switched off when you want to drop it
• how can electromagnets be used in other circuits to act as switches?

  when a large current flows in the wire around the electromagnet, the magnetic field of the electromagnet is strong enough to attract the iron catch. The catch moves down and this breaks the circuit