Generating Electricity Flashcards
if a magnet is placed near a wire, causing the electrons in the wire to feel a force and move, what is the technical name of this force (other than magnetic force)
electromotive force (emf)
why can the magnetic force be called an emf in this case
- because it is creating / inducing the electric current within the wire
- and emf is a force that results in the creation of electric charge
what can we use this principle to do
generate electricity
how would you induce an alternating current within a wire using this method
by reversing the direction of the magnetic field at set intervals
how does the reversing of the magnetic field induce an alternating current
- it would reverse the direction of the force on the electrons
- therefore reversing the polarity of the emf
- so the electrons would flow in the opposite direction
what does faradays law state
- that the induced emf in a wire is proportional to the rate of change of flux linkage
- in other words, a magnetic field that changes more dramatically will induce a larger emf in the wire
therefore what two things could be practically done to increase the induced emf within a wire
- change the direction of the field at a quicker rate
- or increase the strength of the magnetic field that is changing
- (assuming the time between the change from max value to 0 remains the same)
what does the term magnetic flux linkage mean
- the magnet induces a current within the coil due to its magnetic field
- the current within the coil then produces its own magnetic field because of this
- this would be equal and opposite to the one produced by the magnet
- this is what ‘links’ their magnetic flux
why would the magnetic field produced by the current in the wire be equal and opposite to the magnets field
cuz newtons third law says so
if you were to drop a magnet and stone with the same mass through a copper tube (and the same friction), how would the time in which they come out of the other end compare
the magnetic will take longer to come out of the other end
what is the FALSE reason for this
- that copper is magnetic (it isnt)
- so the magnet is simply attracted to the tube
what law explains what is happening here
lenzs law
what does lenzs law state
- that the direction of an induced emf is such that is opposes the change creating it
- basically the newtons third law shit i mentioned before, but idk about the ‘ equal’ part, just be safe and leave it out i guess
think of the copper tube as a series of copper coils all stacked on top of each other. how does lenzs law explain why the magnet falls through the tube at a slower pace than the rock
- as the magnet falls down, its magnetic field is changing relative to each electron in the tube
- this induces an emf in each copper circlet
- causing a small current to flow around the tube
- the circling current will generate its own electromagnetic field, which will exert an opposite force on the magnet
- top tip, in an exam you should mention how the rock generates no field and so none of this occurs
what is the result of this opposite force exerted on the magnet
- it reduces F in F(resultant) = ma
- as mass isnt changing its reducing its acceleration down the tube
- and therefore reducing the speed of the magnets fall
how would you find the direction of an induced emf, when given the direction of the field and motion
- flemings right hand rule
- same finger setup for the left hand rule, just on the right hand
what does each finger stand for
- thumb = motion
- first finger = field
- second finger = induced emf
does it matter that for the right hand rule the second finger is labeled induced emf and not current
- yes
- because the direction of the emf is also the direction the electrons would flow in
- and the second finger with current points in the direction of conventional current
why do you use the right hand for finding out the direction of the induced emf
- because the emf would be opposing the change producing it
- so it would be pointing the opposite direction
if the equation for flux linkage = NBA according to faradays law, what would be the equation for induced emf according to lenzs law
emf (e) = - delta NBA / delta t
why does the equation for emf turn out that way
- induced emf is the rate of change of flux linkage, so it just be divided by time
- the -ve sign is there to indicate the opposing direction of the emf
When a magnet is passed though a metal ring (south pole first) why does the ring move in the same direction as the magnet (not the long ass explanation)
- the induced magnetic field from the ring and the magnetic field from the magnet interact
- because they’re opposing (lenzs law) they are attracted to eachother
- so the ring moves towards the magnet
