11.1 Magnetic Flux And Induced EMF Flashcards
What is magnetic flux?
The product of the magnetic field through a loop, the area of the loop and the cosine of the angle between the field and the normal to the loop § = BAcos@
What is magnetic flux linkage?
The product of the flux through a loop times the number of turns of the wire around the loop. If the loop contains N turns of wire the magnetic flux linkage through the loop
& = N§ = NBAcos@
What is Faraday’s law?
The EMF induced in a loop is equal to the negative of the rate of change of magnetic flux linkage with time emf = - delta$/delta t
What is Lenz’s law?
The direction of the induced EMF is such as to oppose the change in flux that created it. This is a restatement of the law of conservation of energy.
If the field is parallel to the surface what is the flux in the loop?
Zero.
If the field is normal to the surface what is the flux in the loop?
Maximum.
If the loop is made of conducting wire what will the emf do?
Produce a current.
What is the first important application of Faraday’s law?
The magnetic field strength is increasing with the loop inside the field - to find the rate if change of flux linkage use the formula
delta &/delta t = N(delta B/delta t)A and this also gives the induced EMF.
What is the second important application of Faraday’s law?
A rod is pushed steadily to the right of a magnetic field with speed v so the area of the loop decreases thus decreasing the flux linkage in the loop. The rate of change in flux linkage is delta &/delta t = delta(BLx)/delta t = BL(delta x/delta t) = BLv
What is the third important application of Faraday’s law?
A loop is rotating at a constant angular speed about a vertical axis in a constant magnetic field directed horizontally to the right. The loop rotates about the axis with constant angular speed d@/dt = w = 2pif. Hence @ = 2pift. The flux through the look changes because the angle between the loop and the field changes.
In the applications of Faraday’s law how can Lenz’s law be introduced?
It can be used to find the direction of the induced current.
What does Lenz’s law state if the flux is increasing?
The induced current must produce a magnetic field opposite to the external field.
What does Lenz’s law state if the flux is decreasing?
The induced current must produce a magnetic field parallel to the external field.
Why will an EMF be induced an both ends of a rod in a magnetic field?
Esch electron in the rod moves with speed v relative tot he magnetic field and so experiences a magnetic force of magnitude Fm = eve and directed to the left. Electrons will therefore move towards the left end of the rod making it negatively charged and the right end positively charged. An electric field E will therefore be established in the rod, eventually the electric and magnetic forces will be equal and thus eve = eE –> E = vB. This means there will be an EMF induced at the ends of the rod of magnitude V such that E = V/L so V = BLv.
