Magnetic Fields Flashcards
(29 cards)
How do magnetic fields compare to electric fields?
Both can be attractive or repulsive, but magnetic monopoles cannot exist independently
What is magnetic flux?
We can think of flux a bit like charge for an electric field
The unit of flux is the Weber (Wb)
What do magnetic field lines indicate?
They go from North to South, and indicate the direction that a north pole would travel if placed into the field at that location
What is magnetic flux density?
Flux per unit area, measured in Tesla
It can be thought of like field strength for a magnetic field, but don’t call it that!
What does Fleming’s Left Hand Rule describe?
The direction of the magnetic force on a current-carrying conductor or moving charge in a magnetic field.
What is the mnemonic for remebering Fleming’s Left Hand Rule?
Going from thumb to middle finger spells ‘FBI’.
What type of force is the magnetic force on a moving charge?
It is a centripetal force, causing charged particles to follow circular paths.
It’s centripetal because the direction of the force is perpendiculr to the direction of motion
What does Fleming’s Right Hand Rule indicate?
The direction of the magnetic field around a current-carrying conductor.
What does Faraday’s Law of Induction state?
The induced EMF is directly proportional to the rate of change of flux linkage.
What is flux linkage?
The amount of flux passing through a loop.
How can flux linkage be increased?
By increasing flux density, making the loop bigger, or adding more loops.
What is an alternator?
A device that generates alternating current using the principles of electromagnetic induction.
What is motional EMF?
An EMF induced by movement relative to a magnetic field
ε = B l v
What does Lenz’s Law state?
The direction an induced current is such that creates a magnetic field in opposition to the field that produced it
How can Lenz’s Law be demonstrated?
By placing a conductive ring over a coil connected to an AC power supply, which creates an opposing magnetic field, causing the ring to levitate
What is the primary problem with long-distance electrical transmission?
Energy loss due to resistance in cables
How did Nikola Tesla propose to solve the transmission problem?
By increasing the voltage and decreasing the current
What happens to alternating current in transformers during transmission?
AC is stepped-up to high voltage and low current for transmission
True or False: Direct current in the primary coil creates a fluctuating magnetic field.
False
Why should the secondary coil be placed as close as possible to the primary coil in a transformer?
To maximize the amount of magnetic flux encountered by the secondary coil
What type of core is recommended for transformers to enhance efficiency?
Iron core, specifically soft iron due to its high permeability
Why are transformer cores laminated?
To reduce energy loss due to eddy currents
How can resistive losses in transformer coils be minimized?
By making the coils as thick as possible
What is the frequency of the AC power supply in the UK?
50 Hz
