Magnetic Fields Flashcards
What is required for a magnetic field to be induced?
A current must flow through a wire
How can you identify the direction of concentric rings around a wire?
Through the right hand rule
What is magnetic flux density?
It is a measure for the strength of a field
What happens when a field is perpendicular to the current of a wire
A force is exerted onto a wire
What does each finger represent in flemings left hand rule?
Thumb = motion of the force
first finger = direction of field
second finger = direction of conventional current (opposite to electron flow)
What is the direction of a field
It is from north to south
Why do particles follow a circular path in a magnetic field
Force exerted is always perpendicular to the direction of motion, as the force induced acts as a centripetal force
Where can you find the application of charged particles in a magnetic field
In a particle accelerator called a cyclotron
List the characteristics of a cyclotron:
- made up of two dees
- has a uniform field perpendicular to the plane of electrodes
- has high alternating voltage
- the particles speed does not increase due the magnetic field
- the particles speed is accelerated by the electric field when crossing the gap
- when the particle reaches the gap again the AC changes to allow acceleration again
- the radius increases every time
What is magnetic flux
The value which describes the magnetic field or magnetic field lines passing though a given area, when the field is perpendicular to an area
What is magnetic flux linkage?
Magnetic flux multiplied by the number of turns (N)
What happens when a current is not perpendicular to the magnetic field
There is components of magnetic flux found in the perpendicular components of the current found by using trigonometry
What is electromagnetic induction?
This is when conducting rods move relative to a magnetic field, the electrons in the rod will experience a force and build up to one side of a rod causing an emf to be induced
What are the two laws that govern the effects of electromagnetic induction?
Faraday’s law - magnitude to induce emf is equal to rate of change of flux linkage
Lenz’s law - direction of induced current is such as to oppose the motion causing it
What is the peak to peak value of voltage in the UK’s power line
650V
What is the UK’s RMS voltage
230
How do you calculate RMS voltage
peak volatge / root 2 (325/root 2) = 230V
what is the mean voltage of UK power
0 because alternating current goes negative and positive
How is an eddy current occur in a transformer
When magnetic field changes
- emf in the core is induced
- this causes current to flow in the core
How can you reduce loss due to eddy current
By laminating the core
How do you reduce loss in a transformer?
- using thicker wires
- using an easily magnetised core
- laminating the core
How does acceleration impact the path of a proton in a cyclotron
Proton spirals outwards
- as velocity increases the radius increases
What electromagnetic radiation has the same wavelength of a proton
gamma rays
Define magnetic flux density
It is the flux density that produces a force of 1N per 1m of wire when current is 1A
How does a transformer induce emf?
When the AC changes the magnetic field,
this induces emf use to rate of change of flux linkage
What would happen in a velocity selector if the ion emitted had a slower speed than normal?
slower ions would be deflected more
If two coils are next to each other and an emf is induced due to the first coil onto the second coil, how long will this emf last
Momentarily
If flux is decreased what happens?
An emf is induced to oppose magnetic flux, leading to a current on the opposite direction
What properties of a magnet, coil and spring needed to make a geo phone sensitive?
Strong magnetic field
many coil turns
low spring constant springs
large mass magnet
low resistance coil
explain the function of the core
Provides greater linkage
Explain function of secondary coil
It is a conductor with varying magnetic flux
Produce an emf determined by the number of turns
Explain the function of a laminated core?
laminated core made from highly resistive materials,
this reduces eddy current
thin sheets of iron is used, so smaller emf are induced in the core
