topic 12 magnetism and the motor effect Flashcards
What magnetic poles attract and which repel
Like pole REPEL
opposite poels ATRACT
which materials are magnetic
iron, nickel and cobalt
Alloys can be magnetic as contains magnetic material for example steel contains iron
what is the difference between permanent magnets and induced magnets
Permanent magnets produce their own magnetic field all the time.
Induced magnets only produce a magnetic field while they are in another magnetic field.
What happens when you put magnetic material into a magnetic field
It becomes an induced magnet.
This magnetic induction explains why the force between a magnetic material is always attractive.
What happens when you take away the magnetic field for the induced magnet
The induced magnet returns to normal and stop producing its own field. How quickly they lose their magnetism depend on the material they are made of.
“Soft” material lose their magnetism very quick e.g. pure iron
“hard” material lose their magnetism slowly.
uses of magnetic material
Fridge doors, cranes, doorbells, magnetic seperators, maglev trains
How do you tell the strength of a magnetic field
the concentration of lines drawn
How is a bar magnets magnetic field drawn
Lines go from north to south
Closer lines together the stronger the field
The further away from the magnet the weaker it gets.
Strongest at poles of the magnet.
what is the use of plotting compasses to show the direction and shape of a magnetic field
inside the compass is a tiny bar magnet.
The compass lines up with the magnetic field it’s in.
You can place a magnet on piece of paper and move a compass along its magnetic field lines to determine direction and shape of field.
how do compasses show the earth is magnetic
when not in a magnetic field the magnet points towards the north pole. Earth generates its own magnetic field so the core has to be magnetic
how does a moving charge create a magnetic field
When a current flows through a straight, long conductor a magnetic field is created around it.
The field is made of concentric circles perpendicular to the wire.
Changing the direction of the current changes the direction of the field
How do you determine the direction of current in a charged wire
With the right hand thumbs up rule
What factors effect the strength of the field around a moving charge
distance from the wire
Strength of current
how can you increase the strength of a single loop of current carrying wire
you can wrap it into a long coil with lots of loops called a solenoid
what is a solenoid
A long coil of wire.
What is the strength and direction of the magnetic field in and around a solenoid
The field lines of the coils of wire line up.
Inside the solenoid- you get a field lines pointing in same direction. The field is strong and uniform.
Outside the coil- overlapping field lines cancel out each other. So the field is weak apart from ends of solenoid.
what is solenoid an example of
An example of an elctromagnet- a magnet that can be turned on and off
How do you increase the strength of a solenoid
Putting iron block in the centre of the coils- iron core becomes an induced magnet.
Add more coils
Increase current
Describe the motor effect
When a current carrying conductor is put between magnetic poles, the two magnetic fields interact and the wire experiences a force. While the magnets experience an equal and opposite force.
when is a proper force induced on the wire during the motor effects
1) The wire has to be at a right angle to the magnetic field. If wire runs along the magnetic field it won’t experience any force at all.
how do you change the direction of force on wire in the motor effect
the force acts in the same direction relative to the magnetic field and direction of current. so changing direction of either the magnetic field or the current will change the direction of force.
What is the cause of the force on wire in the motor effect
The interaction between the two magnetic fields
How do you use flemmings left-hand rule to determine the direction of the force acting on the wire, the direction of magnetic field and current
Using left hand -
point First finger in the direction of the magnetic Field.
seCond finger in the direction of current
ThuMb direction of force (Motion)
How do you find the size of the force acting on the wire in the motor effect.
F(N)=B(T)I(A)L(M)
B= magnetic flux density- How many field lines in the region (strength of magnetic field.
I= Size of the current
L= length of wire (conductor)
How is the motor effect used in Motors
A current carrying wire rotates in a magnetic field.
1) A wire carrying a current is between two poles and force acts on two side arms of the coil.
2) The forces acting on each arm move in opposite directions due to direction of current, so the coil rotates
3) A split-ring commutator swapps the contacts every half turn to keep it rotating in the same direction.
