12) Magnetism & the Motor Effect Flashcards
What does magnetism describe?
The ability of magnets to attract and repel other magnets
What poles do magnets have?
North pole
South pole
What happens when like poles on a magnet are close together?
They repel
What happens when opposite poles on a magnet are close together?
They attract
What are the 3 pure metals that can be turned into magnets?
Iron
Nickel
Cobalt
(steel is not a pure metal)
What are metals that can be turned into magnets called?
Magnetic materials
What are properties of magnetic materials?
They don’t always act as magnets
Can be attracted but not repelled
Non-magnetic materials will never be attracted
What type of magnets are always magnetic even when they are not near other magnets?
Permanent magnets
What do permanent magnets produce?
Their own electric field
When do magnetic materials temporarily become magnets?
When close to a permanent magnet
What force is always between an induced magnet and a permanent magnet?
An attractive force
What are induced magnets?
Magnetic materials that become magnets when they are in a magnetic field
When will magnetic materials stop being a magnet?
When moved away from a permanent magnet
What do permanent magnets induce in magnetic materials?
Temporary poles
How do temporary poles align with permanent magnets?
So that the magnetic material is attracted to the permanent magnet
What pole will be induced to a magnetic material if it is next to the north pole of a permanent magnet?
A south pole
What type of magnetism is when a magnetic material temporarily becomes a magnet when it’s close to a permanent magnet?
Induced magnetism
What are magnetic forces caused by?
Invisible magnetic fields
What is a magnetic field?
The area around a magnet where another magnet or magnetic material feels a force
What does the strength of a magnetic field depend on?
The distance from the magnet
Where is the magnetic field of a magnet strongest?
At the magnet’s poles
What do magnetic compasses contain?
Small bar magnets
What do arrows on magnetic field lines show?
The direction of a magnetic field
What direction do magnetic field arrows always point?
North pole to south pole
What is the strength of a magnetic field at any point indicated by?
The density of the field lines at that point
Where does a compass needle point to?
The direction of the Earth’s magnetic field
What provides evidence the core of the Earth is magnetic?
The magnetic field around Earth with poles at the North and South
What magnetic pole is the Earth’s geographical N-pole?
Magnetically south
What type of magnet does the Earth’s core behave as?
A bar magnet
What do compasses that are mounted vertically show? (dipping compass)
The Earth’s magnetic field enters the Earth at different angles in different places
What colour is north on a bar magnet?
Red
What colour is south on a bar magnet?
Blue
What type of field does any electric current produce?
A magnetic field
What are the magnetic field lines around a single conducting wire?
Circles
What does the strength of a magnetic field created by an electrical current depend on?
Size of current
Distance from wire
When gripping a wire with your right hand, what do your thumb and fingers show?
Thumb- direction of current
Fingers- direction of magnetic field
What is a solenoid?
A loop of wire coiled into a cylindrical shape
What are the magnetic field lines inside of a solenoid?
Parallel closely spaced lines
What do the individual magnetic fields from each individual coil of a solenoid add up to create?
A strong almost uniform magnetic field around the coil
What are the magnetic field lines outside of a solenoid?
Like a bar magnet, with a clear north and south pole
Where is the magnetic field weaker in a solenoid?
Outside
How does the strength of the magnetic field change for a straight wire?
Strongest closest to the wire
How does the strength of the magnetic field change for a solenoid?
Inside- stong and uniform
Outside- decreases in strength the further away
What changes the magnetic field strength for both solenoids and straight wires?
The size of the current
What is the unit for magnetic field strength?
Magnetic flux density (B)
What is magnetic flux density measured in?
Tesla (T)
What is the equation for magentic force produced?
force produced = magnetic flux density x current x length of wire
F = B x I x L
What 3 things is the force on a wire in a magnetic field directly proportional to? (dependent on)
Strength of magnetic field
Length of wire
Current through wire
Why do coils carrying an electrical current in a motor rotate in a magnetic field?
The current going up one side of the coil is flowing in the opposite direction to the current coming down the other side
What does a split-ring commutator do every half-turn of a coil?
Reverse the direction of the current
Why do split-ring commutators reverse the direction of the current?`
To ensure the current is always moving in the right direction to keep the coil rotating
What 3 ways can increase the size of the turning force acting on a coil carrying a current?
Magnetic field strength
Current through coil
Number of coils in wire
What happens to the direction of a magnetic field as the direction of current changes?
The magnetic field direction changes
What do stationary magnets do to electromagnets inside coils with a changing current?
Repeatedly attract and repel the electromagnet
How do electromagnets inside speakers create sound?
1) Change in current through coil changes magnetic field direction
2) Changing field direction attracts and repels electromagnet to stationary magnet
3) Speakers vibrate backwards and forwards
4) Sound waves are produced
What is converted to sound waves by a speaker?
Electrical signal
What does Fleming’s left hand rule determine?
The direction of force in the Motor Effect
What does each finger mean in Fleming’s left hand rule?
First finger- direction of magnetic field
Second finger- direction of current
Thumb- direction of force (direction conductor would move)
What is the motor effect?
A wire carrying a current creates a magnetic field
What are electromagnets?
Solenoids containing iron cores
What does the catapult experiment show?
A wire carrying a current in a magnetic field experiences a force
What is the process of the catapult experiment?
When power supply is on a current flows in free wire causing it to move
Swapping poles of the magnet will reverse free wire’s direction of movement
Swapping wires connecting to power supply reverses direction of current
Reversing direction of current reverses direction free wire moves
