Topic 10 - Electromagnetic Induction and Magnets Flashcards
permanent magnet
a magnet that is always magnetic, such as a bar magnet
magnetic field
Space around a magnet where it can attract magnetic materials
induced magnet
When a piece of magnetic materials is in a magnetic field it becomes a magnet self
how can the shape of a magnetic field be found?
using a plotting compass
which ways do the lines in a magnetic field flow from
North to south
when is a magnetic field strongest
when the lines are closest together (closest to the poles)
How is the earths magnetic field caused
by electric currents in the molten outer core
How does the strength of the magnetic field depend on the size of the current?
The higher the current the stronger the field
electromagnet
A coil of wire with a current flowing through it
When is the magnetic field strongest around an electromagnet
It’s stronger closer to the wire and gets weaker with increasing distance
what is the magnetic field like around a wire
it’s in multiple circles around the wire
-> strength of magnetic field depends on size of current
-> if current changes direction so does the direction of magnetic field
solenoid
a wire made into a coil
what is the magnetic field of a solenoid like outside and inside the solenoid
The magnetic field from all the different parts of the wire form an overall magnetic field like the one around the bar magnet
-> the fields from individual coils add together to form a very strong field inside the solenoid
-> outside the solenoid the fields from one side of the coil tend to cancel out the fields from the other side to give a weaker field outside
how can the magnetic field of an electromagnet be made stronger?
- putting a piece of iron inside the coil -> this iron becomes a temporary magnet (it is only magnetic when the field from the electromagnet is affecting it)
- more coils of the wire
motor effect
when a wire with current flowing through it is placed in a magnetic field experiences a force - this effect is a result of two interacting magnetic fields
-> One is produced around the wire due to the current flowing through it
-> The second is the magnetic field into which the wire is placed, e.g. between two magnets
What magnetic fields are produced when a wire is placed between two magnets? (Force)
- The wire carrying a current experiences a force when it’s place between the two magnets as the current in the wire create a magnetic field around the wire and interact with the magnetic field between the magnets
- the force is greatest when the wire is at right angles to the magnetic field produced by the magnet and when the wire is in the same direction as this magnetic field
What is Flemming’s left-hand rule?
It shows how the directions of the force, magnetic field and current are related when a wire is placed in between two magnets
What’s the equation for the size of force on conductor carrying current at right angle to magnetic field?
Magnetic field strength (magnetic flux density) x current x length of wire
What causes an electric motor to rotate
The force on a conductor in a magnetic field is used to cause rotation in electric motors
What are ways to increase the total force turning the coil? (ELECTRIC MOTOR)
Using a coil with many turns of wire
function Split ring commutator in an electric motor
changes the direction of the current every half turn by swapping the positive and negative connections of the wire which ensures that the force acting on the coil always turn it in the same direction
When can a voltage or potential difference be induced (electromagnetic induction).
- when the wire experiences a CHANGE in the magnetic field
- If a wire is moved into a magnetic field or magnetic field is moved near the wire
-> this induced p.d. causes a current to flow -> only happens of ends of wire connect (close circuit)
size of induced p.d. depends on…
- number of turns in a coil of wire
- strength of the magnetic field
- how fast the magnetic field moves past the coil
What happens to the p.d. if you reverse the direction of the magnetic field change?
It reverses the direction of the induced potential difference