Magnetic fields Flashcards
What happens when current passes through wire?
Magnetic field is induced forming concentric rings
What is magnetic flux density and its unit?
measure of the strength of field, T (tesla)
How to have a maximum force exerted on wire?
Current must be perpendicular to the field
What is the equation of a charged particle following a circular path?
BQV = mv2 / r
What is supplied to cause the charged particles to move in cyclotron?
high frequency alternating voltage
Why charged particle travel in a semi-circular path in dee
The charged particle experiences a force due to the magnetic field which is perpendicular to the direction of travel.
Force acts as centripetal force for a circular motion
What happens when the particles reach the edge?
They are accelerated by electric field which causes them to move across. When it reaches again, the alternating electric field changes direction so accelerated again (etc.)
What is magnetic flux (phi)
the magnetic field passing through a given area
equation of magnetic flux linkage
N(phi) = BAN
How is emf induced in rod? (electromagnetic induction)
When rod moves relative to a magnetic field, the electrons experience a force. Thus builds up on one side.
What is Faraday’s law
The magnitude of induced emf is equal to the rate of change of flux linkage
What is Lenz’s Law?
induced emf acts in such a direction to produce effects that oppose the change causing it.
- In Lenz’s law experiment, what happens as the magnet approach the coil?
there is a change of flux through the coil so an emf and current is induced
- In Lenz’s law experiment, due to Lenz’s law, what happens to the magnet?
pole will be induced in order to repel the magnet thus slowing it down due to electrostatic force of attraction
- In Lenz’s law experiment, what happens to magnet as it passes through coil?
no change in flux, so no emf is induced
- In Lenz’s law experiment, what happens to magnet as it leaves?
there is a change of flux so a current is induced that opposes the motion of magnet which then attracts the magnet moves up
Where is the peak voltage?
distance from equilibrium to max point
root mean square voltage?
average of all squares of the possible voltages
root mean square voltage?
average of all squares of the possible voltages
In step-up transformer, which one has more turns
secondary has more than primary
What is the main cause of energy loss in transformer?
eddy currents which are induced by alternating magnetic field in primary coil and form a loop
How are eddy current formed?
Eddy current oppose the field that produced the,. reducing field’s flux density and causes energy to be lost
Effects to reduce eddy currents (laminated iron core) -made out of, causes
laminated iron core - core is made up of layers of iron between insulator. This is because eddy current cannot pass through insulator so amplitude decreases.
another effect to reduce eddy currents
high resistivity metal
How to reduce energy loss in resistance in coil?
thick wire
How to reduce energy loss if core not easily magnetised?
soft iron core allow easy magnetisation and demagnetisation
How to reduce energy loss if core not easily magnetised?
soft iron core allow easy magnetisation and demagnetisation
