Transformers Flashcards
what do transformers do
- they step up or step down pds
- by having a coil with a current and magnetic field
- induce an emf and therefore current within the other coil
what is the name of the coil producing the initial magnetic field
the primary coil
what is the name of the coil that is having an emf induced within it due to the magnetic field of the primary coil
the secondary coil
what needs to be in the setup for the primary coil in order for this induction to work (other than a cell) and why
- a switch
- because there needs to be a change in the magnetic field (the second coil is feeling) in order for an emf to be induced
- as faradays law states
if the switch is simply held down, producing a constant magnetic field, what would eventually happen to the current in the secondary coil
- there will be no change in flux linkage overtime
- so the induced emf would drop to 0
- meaning theres no current or pd present anymore
if a voltmeter was connected to the secondary coil, what would it show from the moment the switch was held down to about a couple of seconds later
- it would initially show a spike in pd across the coil
- then would promptly die back down to 0
what would be seen on the voltmeter if the switch was opened again
- there would be another spike in the pd across the coil
- but it would be equal and OPPOSITE to the first spike
- either by a needle kicking the opposite direction or by showing a -ve reading
- then once again promptly returning back to 0
why does the voltmeter behave like this when the switch is opened again
- when opened, the primary coil of wire stops producing a magnetic field
- this results in there being a change in the flux linkage
- so an induced emf would be temporarily produced in the secondary coil
- but in the opposite direction
why does the induced emf within the secondary coil alternate at the same rate as the ac current supplied to the primary coil
- the magnetic field produced by the p coil would alternate at the same rate as the ac current
- the alternating magnetic field would induce the emf that would alternate at the same rate as said magnetic field
- aka the induced emf would alternate at the same rate as the ac current supplied
recalling the equation for flux linkage, what would the strength of the coils’ magnetic fields in this transformer setup depend on, given B and A are equal in both
- flux linkage = NBA
- so the number of turns the coils have would determine the strength
if the rate of change of flux linkage determines the emf present within the coils, and the rate at which the current in both wires alternates is equal, what equation can you derive for the relationships between both coils number of turns and the pd across their wires
- the ratio of the coils’ number of turns would equal the ratio of the emf / pd across them
- Vp / Vs = Np / Ns
what would that equation be in words
the pd across the primary coil over the pd across the secondary coil = the number of turns of the primary coil over the number of turns of the secondary coil
now that you know this equation, what would the setup of a step up transformer be like
- the secondary coil would have more turns than the primary coil
- which would increase the output voltage compared to the input voltage
what would a step down transformer be like
- the secondary coil would have less turns than the primary coil
- which would decrease the output voltage compared to the input voltage
where are the magnetic fields these two coils of wire produced (describe in the sense of it being a picture)
- the magnetic fields of both would create a circle
- that would circle around the inside of the iron core
- usually clockwise
