Mag Fields Flashcards
What is the proper name for magnetic field strength and what are the symbol and unit?
Magnetic flux density.
Symbol: B
Units: T, wbm^-2
Which way do magnetic field lines go?
From North to South
What three things can you do to increase the speed of a motor?
Increase the number of turns on the coil, increase the p.d. across it and increase the srength of the magnetic field.
What does a step-up transformer do?
Increases the voltage and decreases the current so there is less energy lost as heat due to resistance of cables.
What should ideally be constant for both sides of a transformer?
Power
For a step-up transformer, what is different about the secondary coil compared to the primary coil?
It has a greater number of turns which will increase the flux linkage ‘captured’
What three parts of a transformers design ensures as little energy is lost as possible?
Low resistance windings in the coils.
Soft iron core so its easily magnetised.
Laminated core which reduces eddy currents induced in the core.
What happens if a particle enters a field at an angle to the direction of the field?
The components of the velocity of the particle are affected.
What do you have to be careful of when applying the LH rule to free charges?
For electrons, the velocity of the particle is in the opposite direction to the current.
For a cyclotron, why must there be an alternating p.d. across the D’s and what is the frequency of this equivalent to?
To accelerate the protons across the gap, increase the radius.
The frequency of the p.d. is equal to the frequency of the protons (Frequency is independent of Radius)
What is Lenz’s Law?
The direction of an induced current/emf is such that it will oppose the change that caused it.
In other words the currents will fight back with their own opposing mag field.
What is always needed for a current to be induced in a coil and how is this achieved in a transformer?
The wire needs to experience varying flux.
In a transformer, it will only work if AC is used in the primary coil as it creates a fluctuating field.
What is Faraday’s Law?
The induced emf is proportional to the rate of change in flux.
How do you calculate the power lost due to heat in overhead cables?
Find current from P = IV.
Then use P=I^2R.
