Magnetic Fields Flashcards
Why does a charged particle have a constant speed in a magnetic field?
It is because the magnetic force always acts perpendicular to the direction of motion (velocity).
The reason it acts perpendicularly is because current acts in the direction of motion, I and B always act perpendicular to each other.
Prove that the time to travel one semi circle in a cyclotron is independent of the radius.
BQV = mv²/r V = d/t d = πr (for semicircle) BQ=mv/r BQ=mπr/rt t= mπ/BQ Therefore time is independent of radius.
What is the reason that the side with more turns in a transformer has a higher voltage?
Because induced emf is directly proportional to the change in magnetic flux linkage and because magnetic flux linkage is directly proportional to the number of turn, this means the more turns the greater the emf.
What is the purpose of the soft iron core in a transformer?
To guide the magnetic field to the other coil.
Extra:
No current passes through the iron core.
How are eddy currents formed in the soft iron core?
Because an alternating current is passing through the primary coil a constant change in magnetic flux is generated in the conductive iron core. As a result of Lenz’s Law an opposing emf is induced and therefore current is induced in the iron core which weakens the magnetic field strength of the primary coils field and causes heating which reduces transformer efficiency.
Why is a.c currents used in transformers?
Because there has to be a change in magnetic flux in order to induce an emf in the secondary coil.
(d.c would just make a permanent magnet)
Definition of Lenz’s Law.
The DIRECTION of the INDUCED EMF is such that it will OPPOSE the change (in magnetic flux) that is causing it.
Define Faraday’s Law
The INDUCED EMF created in a conductor is directly proportional to the rate of change in magnetic flux linkage through the conductor.
Why do we use a soft iron for the core rather than other materials?
Becasue it is easily magnetised and demagnetised which increases efficiency.
What can we do to reduce the eddy currents in a transformer?
And explain the process
Laminate the soft iron core,
This is where you would split the core into small sections with non-conductive material in-between the iron to reduce the maximum current generated, as current is directly proportional to area.
