Generators EMF from Motion A moving conductor causes

Generators

EMF from Motion ] A moving conductor causes electrons to move. • Magnetic force applied to electrons ] The electrons drift to one end. • Create an electric field • Matching EMF ] At equilibrium forces balance.

Falling Bar ] A bar 1. 0 m long is dropped in an east-west orientation. The earth’s field is 2. 0 x 10 -5 T. ] Find the induced EMF after the bar falls for 4. 0 s. ] The problem gives the length and the field, but the velocity is needed. • • Use basic kinematics v = v 0 + gt v = (9. 81 m/s 2)(4. 0 s) v = 39 m/s. ] Now use the equation for induced EMF. • E = v. BL • E = 0. 78 m. V

Cutting Lines ] As the sliding bar moves the circuit increases in size. ] The area increases by a rate equal to DA/Dt = v. L. ] The number of field lines cut per second is the area change times the field. • v. LB in a uniform field ] The EMF equals the number of field lines cut per second.

Power Bar ] The sliding bar creates an EMF • Potential difference in volts ] The potential can create a current in a resistor. ] There is power output from the moving bar.

Alternating Generator ] A turning loop of wire in a magnetic field generates EMF. • Loop area changes with respect to field lines

AC Generation ] The moving loop alternates creating current one way then the other. • • Sinusoidal pattern Loop turns at rate w=q/t EMF based on loop area Extra turns increase the EMF ] This is called alternating current or AC.

DC Generator ] A DC generator can be made by using a commutator and brushes. • Like a motor • Voltage pulses but doesn’t reverse ] Better DC generators use multiple commutators. next