What do magnets produce?
- all magnets produce a magnetic field (a region where other magnetic maturely experience a force)
- the field lines go from north to south
- the magnetic fields are strongest at the poles of a magnetic so the magnetic force is too
- Close field lines are together the stronger the force
What magnets attract each other?
Unlike magnetic pole attract and like magnetic poles repel
How do you create a uniform field?
- Placing the north and south poles of two bar magnets near each other creates a uniform field between two poles
- placing two north’s or souths towards each other leads to repulsion
How can plotting compasses be used to show magnetic fields?
- inside a compass there is a needle (small bag magnet)which always lime up with the magnetic field it’s in
- put the magnet on paper and draw around it
- place the compass on the paper near the magnet and the needle will point in the direction of the field line at this position
- mark the direction of the needle by drawing two dots either end
- switch the direction of the compass needle and put a dot, repeat and join up the marks made
What do plotting compasses point when not near a magnet and what is this proof of?
They will always point towards the earths’s North Pole as the earth generates its own magnificent field (North Pole is magnetic South Pole)
-this shows the inside of the earth (core) must be magnetic
What is the difference between permanent and induced magnets?
Permanent magnets product their own magnetic field all the time
- induced magnets only produce a magnetic field while they’re in another magnetic field
- therefore by putting any magnetic material in a magnetic field it becomes an induced magnet
What happens when you take away the magnetic field of an induced magnet?
- they return to normal and stop producing a magnetic field, how quickly depend on their material
- magnetically soft materials e.g. pure Iron and nickel loose magnetism very quickly
- magnetically hard materials like steel lose magnetism slowly (permanganate magnets are made from this)
What are some uses of magnets?
- Fridge doors to keep them permanently closed
- cranes use induced electromagnets to attract and move magnetic materials
- maglev trains use magnetic repulsion to make trains float slightly above the track reducing friction losses and to propel them along
What happens when a current flows through a long straight conductor?
A magnetic field is created around it
- the field is mad duo of concentric circles to the perpendicular wire through the centre
- the larger the current or the closer you at the the wire the stronger the field is
What is the right hand thumb rule?
When your right thumb points in The direction of conventional current the direction your fingers turn shows the direction of the magnetic field
-changing the direction of current changes the direction of the magnetic field
What happens when a current carrying wire is out between two magnetic fields?
The two magnetic fields interact and results in a force on the wire
-the wires also exert and equal and opposite force on the magnet
What is Flemings left hand rule?
- used to find direction of the force on a current carrying wire
- your thumb, first finger and second finger must all be 90° perpendicular to each other
- first finger is field, second is current and thumb is motion/Force
How can you find the size of the force?
F= BIL
- B is the magnetic flux density showing the strength of the magnetic field
- L is length of the conductor and I is the size of the current
How could the force on the wire be increased or reversed?
- stronger magnet, greater current, more voltage
- to reverse the force on the wire change the direction of the current or swap the poles around
What is a solenoid?
- a loop of current carrying wire (this increases the strength)
- inside the centre you get lots of field lines pointing in the same direction, forming a very long almost uniform field, so they reinforce so is stronger
- outside the overlapping field lines cancel out so it is weaker
How do you increases the strength of a solenoid?
- placing a block of iron in the centre of the coil which become an induced magnet
- more turns of the coil
What is electromagnetic induction?
Then induction of a potential different which induces a surreal in a wire which is experiencing a change in magnetic field
How do you get electromagnetic induction?
- moving/rotating a magnet in a coil of wire or a conductor in a magnetic field (small local scale in lab)
- if you move or rotate the magnet in the opposite direction then the current will be reversed or if the polarities switch
- if you continually move the magnet /coil backwards and forwards in the same direction it produces an alternating current
What do we mean when the current opposes the change made to it?
- when a current is induced in a wire that current produces its own magnetic field
- the algebraic fie,d created by an induced current always acts against the change
- this creates a changing magnetic field
How do power stations do a large scale generation of electrical energy?
- burn fossil fuels to heat water into steam which turns a turbine
- the turbine is connected to a powerful magnet inside a generator
- as the turbine spins the magnet spins inducing a large PD and a.c. In the coils
- the coils are joined in parallel to produce a single output
How do we used the force on a conductor in a magnetic field to produce rotational movement?
- forces act on the two side arms of the current carrying coil of wire
- these forces act in opposite direction (FLHR) so the coil rotates
What is a dynamo?
- we rotate a coil of wire sitting in a mag.field.
- this produces a current which changes every half term with EM induction
- therefore we use a split ring commutator to switch the polarities every half term so the current travels in one direction (d.c.)
What is an alternator?
- work in the same way as a dynamo by generate a.c.
- so instead of a split ring they use slip rings and brushes so the contacts don’t swap so generate a.c.
What are microphones?
- sound waves but a diaphragm meaning it moves. This moves a coil of wire sitting in a magnetic field
- Louder sound waves move the diaphragm further
- this induces a current in the wire
