Magnetism P2 Flashcards
Which type of radiation is not affected by magnetic fields?
Gamma however all other charged particles are affected by magnetic fields
What can magnetic fields interfere with?
Electric signals
Define lodestone
Naturally occurring magnet. Eventually used as a guide stone by tying it to a piece of string, the first crude compass.
Identify 3 things magnetism is used for nowadays
Technology, electricity, transport
What are bar magnets?
Permanent magnets which means their magnetism cannot be turned on or off like it can with electromagnets
What do bar magnets have?
Two poles (north and south)
How can the earth be thought of as a giant bar magnet?
The core of the earth contains iron which generates a giant magnetic field. One end of a magnetic compass always points north
Why is the magnetic North Pole not the same as the geographical North Pole?
The iron core is slightly molten meaning currents can move about and drift. Sometimes it can completely reverse
Identify 3 magnetic materials
Iron, nickel, cobalt
What 2 things do field lines show on a diagram?
Which direction a force would act on a North Pole if it was put at that point in the field, the closer together the field lines the stronger the magnetic attraction at that point
No matter how many sheets of paper you put between two magnets, why will the newton meter never reach zero?
The newton meter will show the weight of the top magnet
Why might you be unable to experiment with fewer than 10 sheets of paper between two magnets when testing how the force of attraction is dependant on their separation?
The top magnet and newtonmeter separate before magnets separate because the force between magnets is greater than the force between magnet and hook of newton meter
Where is the magnetic field of a magnet strongest?
Poles
What is induced magnetism?
Induced magnets are magnetic materials that turn into magnets when they are brought into a magnetic field but when you take away the magnetic field induced magnets quickly lost all or most of their magnetism
How can you make an electromagnet?
Get a copper wire and remove a few centimetres of the insulation at the ends then wrap the wire around an iron nail in one direction. Attach one end of the wire to the positive terminal of a battery and the other to the negative
Why do you wrap the wire around the iron nail in only one direction?
The direction of the magnetic field depends on the direction of the electric current creating it
How can you make an electromagnet stronger? 4 ways
Have more turns in the wire, keep the wire close to the core, have more current passing through the core, have a thicker core
How could you test if your electromagnet worked?
See if it attracted steel paper clips
Where do field lines go to and from on a diagram?
From north to south
What happens when two poles of a magnet are put near eachother?
They exert a force on eachother which can be attractive or repulsive
How does a compass work?
Inside a compass there is a tiny bar magnet (the needle), the North Pole of this is attracted to the South Pole of any other magnet that is near so the compass needle points in the direction of the magnetic field it is in
Why does a compass always point north when it isn’t near a magnet?
The Earth generates its own magnetic field which shows the inside (core) of the earth is magnetic
How can you identify the field pattern around a magnet? 6 steps
Place bar magnet in middle of paper and trace around, place a compass at one Pole of the magnet and make a dot to show direction of the compass, move compass so the base of the arrow is at the dot and make a new mark at the top of the arrow, keep doing this until you reach the other end of the magnet, connect dots to draw a magnetic field line, repeat again starting at a different point to build up a picture of what the magnetic field looks like
What else can you use to identify a bar magnets magnetic fields shape (but not direction)?
Iron filings (you scatter them and they will give a pattern)
Identify two types of magnets
Permanent and induced
What is the force between permanent and induced magnets?
Always attractive
What happens to induced magnets when you remove the magnetic field?
Induced magnets lose most of all of their magnetism
What is the right hand rule?
Thumb points in the direction of current, fingers curl round in the direction of the field
What happens when a current flows through a wire?
A magnetic field is created around the wire which is made up of concentric circles perpendicular to the wire with the wire in the centre
How can you see the magnetic field around a current carrying wire?
Place a compass near a wire and as you move the compass, trace the direction of the magnetic field
What happens when the direction of current in a wire changes?
The direction of the magnetic field changes and you can use the right hand thumb rule to work out which way it goes
When is a magnetic field around a current carrying wire stronger? 3 points
the closer to the wire you are the stronger it is, the larger the current through the wire the stronger it is, wrap the wire into a coil called a solenoid to make it stronger
What is a solenoid?
Cylindrical coil of wire which acts as a magnet when carrying electric current.
Why is a magnetic field stronger when you wrap the wire into a solenoid?
The field lines around each loop of wire line up with each other which results in lots of field lines pointing in the same direction which are very close to eachother
How can you describe the magnetic field inside and outside a solenoid?
Strong and uniform (same strength and direction at every point in that region). Outside the coil, magnetic field is just like the one round a bar magnet
How can you increase the field strength of a solenoid even more?
Put a block of iron in the centre of the coil. The iron becomes an induced magnet whenever current is flowing but the magnetic field disappears if you stop the current therefore a solenoid with an iron core is called an electromagnet
Identify 3 things electromagnets are used in
Security doors, electric bells, car ignition circuits
What is the motor effect?
When a current carrying wire or any other conductor is put between two magnetic poles, the magnetic field around the wire interacts with the magnetic field it is in which causes the magnet and conductor to exert a force on each other. This can cause the wire to move
Motor effect:What has to happen for the where to experience a full force?
The wire has to be at 90 degrees (perpendicular) to the magnetic field. If the wire runs parallel to the magnetic field it will not experience any force at all. This is because the force always acts at right angles to the magnetic field of the magnets and to the direction of the current in the wire
Motor effect:Identify two ways to increase the size of a force
Increase current, use stronger magnet, increase strength of magnetic field
Motor effect:How can you show direction of the force?
Apply a current to a set of rails inside a horseshoe magnet. A bar is placed along the rails which completes the circuit and generates a force which rolls the car along the rails, the force increases with the strength of the magnetic field and with the amount of current passing through the conductor
Identify four devices which use motors
Leaf blower, hair dryer, drill, vehicle
What is magnetic flux density
How many field lines there are in a region (how strong magnetic field is)
What 3 things does the force acting on a conductor depend on?
Magnetic flux density, size of current through conductor, length of the conductor in the magnetic field
When the current is at 90 degrees to the magnetic field, what equation can you use to find force?
Magnetic flux density (teslas T) x length (m) x current (A)
What is Flemings left hand rule?
Pointing first finger is direction of field, pointing second finger is direction of current, pointing thumb is the direction of the force (motion). This is because direction of force is always at right angles to the wire and field lines
What does Flemings left hand rule show?
If either the current or magnetic field is reversed, the direction of the force is reversed. This rule can be used to find the direction of the force
Why do electric motors work?
A force acts on a current carrying wire in a magnetic field
Why does a coil spin when current passes through?
A force acts on either side of the coil (which is on an axle) due to the motor effect, the force on each side is equal and opposite to eachother as the current is in the opposite direction on each side, the split ring commutator reverses the current around the coil every half turn to keep the motor running
What can you use to find which way a coil is turning?
Left hand rule
How can the direction of a motor be reversed?
By either swapping the polarity of the dc supply (reversing the current) or swapping the magnetic poles (reversing the magnetic field)
