ü The induced electromagnetic force across a conductor is proportional to the rate at which the conductor cuts magnetic flux.
· We can use SI units to equate the emf to the rate at which the flux is cut.
The work done by the force exerted on a wire by a field
is Force * Distance. The force, as we already know, is BIl, so energy supplied E = BIlx. The definition of the electromotive
force E as the energy E
changed from other forms of energy to electrical energy per unit charge Q
E = Q E. Charge Q is the product of current and time so
E = E I t. Combine these two equations:
E It = BIlx, so
E = Blx
· Lenz's Law states that
· The direction of any induced current is such as to oppose the flux change that causes it.
· This means that the emf produced must be negative, as the voltage causing it is taken to be positive, as is the field that it produces, which in turn causes the emf.
· As Blx is the magnetic flux, we can express this as
E = - F
· Or if, according to the original statement, the emf is proportional to the rate of change of flux, calculus notation can be used to produce:
E = - dF
· REMEMBER THIS, IF NOTHING ELSE IN LIFE!
Copyright © Simon van Leishout 2000