12.1.1 to 12.1.4

12.1.1 Describe the inducing of an emf by relative motion between a conductor and a magnetic field: All conductors contain free electrons. As the free electrons move downwards through the magnetic field it will experience a force. Using Flemming's left had rule we can deduce the direction of the force. This force will cause the free electrons move in the direction of the force. Since the electrons are moving towards a particular side of the conductor, this has caused the lattice atoms on the opposite side to the force to become positive and therefore there is a potential difference between the 2 ends of the conductor. 12.1.2 Derive the formula for the emf induced in a straight conductor moving in a magnetic field: Fb = Fe Fb = Bev E = - dV/dx potential gradient = V / L Fe = Ee = Ve / L Ve / L = Bev V = BLv Therefore emf induced = BLv 12.1.3 Define Magnetic Flux and Magnetic Flux Linkage: Magnetic flux is the strength of a magnetic field over a given area A flux passing through a coil of N turns of wire is said to have a link with the coil.Therefore Magnetic Flux Linkage is given by: Flux Linkage = Number of coil turn x Magnetic Flux 12.1.4 Describe the production of an induced emf by a time-changing magnetic flux: ·         An e.m.f. is also produced in a wire if the magnetic field changes with time. The universal rule that applies  to all situations involving emf is stated as: "the magnitude of an induced e.m.f is proportional to the rate of change of flux linkage" State Faraday's law and Lenz's law: ·         Faraday's law:   ·         Lenz's law states that "The direction of the induced e.m.f. is such that if an induced current were able to flow, it would oppose the change which caused it".   Questions Q39 a) emf = BLv               =50x10^-6 x 0.2 x 20 = 2 x 10^-45 b) I = V / R             I=2x10^-4 / 2        = 1x10^-4 c) I^2 R = 1 x 10^-4 x 2 = 2 x 10^-8 W d) Work done = energy dissipated = 2 X 10^-8 e) s = d/t s = 20/1 = 20m/s f) F = work / d = 2x10^-8/20 = 1x10^-9 Q40 a) Total flux = 5000 x 10^-6 x 2 x 10^-4 = 1 x 10^-6 2 x 10^-4 m^2 = 2 cm^2 b) would be a quarter since flux density would be halved and time would be doubled = 0.25 X 10^-6tm^-2s^-1 c) since induced emf = rate of change of flux, the induced emf is 0.25 x 10^-6 V Q41 a) = 6 x 10^-4 x 50 x 500 x 10^-6 therefore total flux = 1.5 x 10^-5 tm^-2 b) Φ = BcosθxA Φ = 500 x 10^-6 x cos30 x 6x10^-4 x 50 Φ = 1.3 x 10^-5 tm^-2 c) Blv = tm^2/s 1.3 x 10^-5 / 3 = 4.3 x 10^-6 V