Magnetic Fields U4 Flashcards
What is the right hand rule
Thumb = current
Curled fingers = Magnetic field direction
What does each finger mean for Flemings left hang rule
Thumb = force
First finger = magnetic field
Second finger = current
Define magnetic field strength
It is a measure of the magnetic field per unit area
What is B measured in
Tesla
Is B scalar or vector? Why?
Vector because it has magnitude and direction
Magnetic flux =
BA
What are the two equations for flux linkage
N x flux
NBA
What’re the units of flux linkage and flux
Weber (Wb)
What happens to a wire carrying a current in a magnetic field
It will experience a force
When does a force act on a wire in a magnetic field
If the wire is carrying current and the wire cuts the magnetic field lines
When is the force zero (acting on a current carrying wire in a magnetic field)
If the current is parallel to the flux lines
What is always the direction of the force always perpendicular to
Current
Magnetic field
F = ? when a current carrying wire at right angles to a magnetic field is proportional to the current
BIL
Define the B from BIL
The force on one metre of wire carrying a current of one amp at right angles to the magnetic field
When is force greatest acting on a current carrying wire
What is this in terms of an equation?
When the wire and field are perpendicular
Bsin(theta)
For a wire at angle theta to the field the force acting on the wire is given by
F = BILsin(theta)
What are the stages of a motor
1) the coil has an electric current round the core and provides a field that interacts with two oppositely poles permanent magnets
2) the fields repel each other causing a resultant force and anticlockwise motion (due to the LHR)
3) as the cool turns half way, perpendicular to current, it gets close to vertical then disconnects from the commutator
4) momentum carries the coil over the vertical point then the commutator reconnects
5) due to there being current flowing again in the cool the resultant force is restored so it spins
When the coil gets to halfway it is perpendicular to what
Current
Why is emf induced in a motor situation
There is a change in flux in the coil
What increasing the emf do to speed
It increases it
Why does the speed increase when the emf increases
Because there’s an increased rate of change in flux
When the magnetic field increases what decreases
Current
When a charged particle has velocity what does it act perpendicular to
What does this cause
Field therefore it has circular motion
