electromagnetism Flashcards
what does a simple transformer consist of?
- core
- primary coil
- secondary coil
what is a step up transformer?
- Number of turns on primary coil is less than number of turns on secondary coil
what is a step down transformer?
- when number of turns on primary coil is greater than number of turns on secondary coil
name the main sources of inefficiency in the core
- eddy currents in the core
- heat loss through the coils
- not all flux from the primary coil going through the secondary coil
- magnetising and demagnetising the core
how can we reduce the sources of inefficiency?
- laminate the core
- use thick copper wires with low resistance
- use a soft iron core
- make the core from a soft magnetic material
what is the transformer equation?
Ns/Np = Vs/Vp = Ip/Is
what is the equation for efficiency of a transformer
Is Vs / Ip Vp
what is the power loss in a wire given by?
I^2 x R
how do transformers work
- we put a step up transformer between power stations and the transmission lines. reducing current, reducing power lost as heat.
- we have a step down transformer before peoples homes to reduce the voltage to a safe level
what are eddy currents?
- a change in magnetic flux through a conductor enduces an emf
- if the conductor is solid, this emf causes currents to flow in loops within the conductor
what is Faraday’s Law?
- the magnitude of the emf induced in a coil is equal to the rate of change of flux linkage through the coil
what is Lenz’s Law?
- the direction of the induced emf opposes the change that caused it
what is magnetic flux?
- magnetic flux density multiplied by the area of the surface, where A is perpendicular to the lines of flux
BAcos€
how can we induce an EMF in a coil?
- change the flux density
- change the area of the coil
- rotate the coil
- movr a coil into or out of a magnetic field
how can we calculate the EMF from a graph of flux linkage against time?
- gradient is the EMF
what is 1 tesla defined as
the magnetic field strength that produces a force of 1N on a 1 metre wire carrying a current of 1 amp
what happens when current passes through a wire?
- a magnetic field is induced
how can we use FLHR to calculate the direction of the force
ThuMb - direction of force
First finger - direction of the field
seCond finger - direction of conventional current
- remember opposite direction to electron flow
what is meant by conventional current?
- current that flows from positive to negative
why does the particle experience circular motion?
- the force induced by the magnetic field acts as a centripetal force
what is the equation for the radius of the particle’s circular path?
r = mv/BQ
r = radius
m = mass
v = velocity
Q = charge
B = magnetig flux density
what is a cyclotron and what is it used for?
- a cyclotron is a particle accelerator that accelerates charged particles through a spiral path using a fixed magnetic firld and an alternating potential difference
what is meant by peak voltage?
- half the peak-to-peak voltage, and is equivalent to the amplitude of the wave form
what is meany br root mean square voltage
- average of all the squares of the possible voltages
- Vrms = Vo/root 2
