(Electro)- Magnetism/ Magnetism Flashcards
Where are the magnetic forces of a magnet?
The poles of a magnet
What are the 2 poles of a magnet?
North/ South poles
What happens when we bring 2 magnets close to each other?
They exert a force on each other
What do 2 like poles do?
Repel each other ( force of repulsion- which forces magnets apart)
What do 2 unlike poles do?
Attract each other (force of attraction- which attracts the magnets)
What type of forces are the attraction/ repulsion caused by? How do we know this?
Non Contact Forces- as the magnets dont have to touch to experience the forces
What is a permeant magnet?
A magnet that produces its own magnetic field i.e bar magnet
What can happen if we bring 2 permeant magnets close to each other?
Can attract or repel the other magnet
What is an induced magnet?
An object that becomes a magnet when placed in a magnetic field— if a magnet is induced, it will only ever be attracted to a permanent magnet
Give an example of how to make induced magnets work
Place permeant magnet between 2 induced magnets which causes a magnetic field around the magnetic field- which causes the 2 objects to become magnets- so they are now induced magnets
What type of force does induced magnetism ALWAYS cause?
Force of attraction as it can only attract magnetic metals NOT repel them
What happens when we take away the permanent magnet from the induced magnet?
Induced magnet loses most/all magnetism quickly
What are the 4 types of magnetic material?
Iron, Steel( an alloy of iron), cobalt, nickel and they can all be made into permeant or induced magnets
What is a magnetic field?
A region around a magnet where a force acts on another magnet or on a magnetic material
What factor does the strength of the magnetic field depend on?
The distance from the magnet ( so the closer the magnets are, the better the strength of the magnetic field)
Where is the magnetic field the strongest at?
Poles of the magnet
How can we find the direction of a magnetic field?
Using a compass
What do magnetic compasses contain? What does this allow?
A small bar magnet so if we place the compass near the bar magnet, we can plot the magnetic field
Explain the proccess of drawing the magnetic field line using just a compass and bar magnet
Get a bar magnet and place the south pole of the compass near the north pole of the magnet. Then draw a cross at the north pole of the compass. Move the compass so that the south pole of the compass is on the previous cross drawn and draw a cross all the way round to the south pole of the bar magnet and connect. Repeat at different points of the north pole of the bar magnet
What does the arrow of on the lines of the magnetic field show us?
Direction of field line
What direction do field lines run?
ALWAYS from the north pole to the south pole
How do we know where the field is the strongest? And where is the strongest part of the field?
Where the lines are closer together and the strongest part of the field= the poles of the magnet
How do we know the earth has its own magnetic field?
If we hold a compass away from any magnets, the needle ALWAYS points in the north south direction.
What causes the earths magnetic field?
The Earths core
What type of force is ALWAYS between a magnet and a magnetic material?
Force of attraction
What direction will a compass needle ALWAYS point in?
Direction of the Earths magnetic field
Describe where the earths southern and northern poles are ( TRICKY)
The earths southern magnetic pole is at the Northern Hemisphere and the earths northern magnetic pole is at the Southern hemisphere
How does the above theory describe why the north pole of a compass’ needle points towards GEOGRAPHIC north?
As its attracted to the Earths south magnetic pole and 2 unlike poles attract
What is convectional current?
Conventional current is the flow of a positive charge from positive to negative
REMEMBER- electrons flow the other way IRL
How can we prove that there is a magnetic field around a wire using a compass?
When the current is turned off, then the compass needle lines up with the Earths Magnetic Field. However, if we turn the current on again then the compass needle deflects which proves their is a magnetic field around the wire.
What is 2 factor that causes the strength of the magnetic field and give examples?
Size of the current so a larger current produces stronger magnetic field.
Magnetic field is strongest closer to wire so as we move further from wire the strength of the MF decreases
What happens if we change the direction of the current?
We change the direction of the magnetic field
direction of current is directly proportional to direction of magnetic field
What rule do we use to work out the direction of the magnetic field produced by a wire?
Right hand grip rule
Place RIGHT HAND on pencil so thumb points in direction of conventional current (upwards). Now the fingers are pointing in direction of the magnetic field
What is another way to increase the strength of the magnetic field?
Coils in the wire (solenoid) so that when we turn on the current we get a strong magnetic field inside the solenoid
What are 3 ways we can increase the strength of the magnetic field produced by a solenoid?
1) Increasing size of current means we increase the strength of the magnetic field
2) The strength of the magnetic field increases if we increase the number of turns of the coil
3) Placing a piece of iron/ iron core inside the solenoid increases the strength of the magnetic field
What is an electro magnet?
A magnet made by wrapping a coil of wire around an iron bar and passing an electric current through the coil.
Why are electromagnets useful?
We can change the strength of the magnetic field by changing the size of the current and also turn it on/off
What is the force equation?
F(N)= M(TESLA) X I( AMPS) X L (M)
force= magnetic flux density x current x length
This equation only applies to a wire which is at a right angles to the magnetic field
What is the magnetic flux density?
measure of the strength of the magnetic field
What 3 factors affect the size of the force?
Current, Magnetic flux density and length of the conductor
For Flemings left hand rule– what does each finger show?
thumb= force
index finger= north- south so magnetic field
second finger= current
What happens if a conductor is parallel to the magnetic field?
It wont experience a force as is not at a right a right angle to the magnetic field
What is the motor effect?
When we place a wire into a magnetic field. The magnetic field around the wire interacts with the magnetic field between the magnets so the wire now experiences a force
What is one useful application of the motor effect?
In electric motors
What is a problem when the loop starts to rotate?
Once the loop is at 90 degrees it stops rotating because if the loop rotated beyond 90 degrees the direction of the current on each side acts in the opposite force from before. So these forces push the loop back to the 90 degree position
How can we solve this issue?
Switch the direction of the current when the loop passes 90 degrees using a split ring commutator which is connected to conducting brushes.
The brushes allow the electric current to pass onto the ring. The current produces a turning force on the motor. The force makes the motor rotate in the clockwise direction.
The current breaks for a ting fraction of a second but the momentum keeps the wire going. Now the current switches direction so the force on one side acts in the original direction
What is a split ring commutator?
A split metal ring
What does switching the direction of current allow?
By switching the direction of the current the split ring commutator allows the motor to keep rotating in the same direction
