CH 23-3

Electric Generator Converts kinetic energy to electrical energy. Typically, water or steam rotates a turbine which rotates a wire coil that is in a uniform magnetic field. (In the case of a gas generator, the moving pistons in the gasoline engine turns a shaft which rotates a coil in a uniform magnetic field.)

t=0 What is the induced emf at this instant?

 t=  /2 What is the induced emf at this instant?

 t=  What is the induced emf at this instant?

 t=3  What is the induced emf at this instant?

emf vs. t

Example A coil of 50 turns and resistance 5  has a radius 2 cm and rotates at a rate of 20 rev/s in magnetic field of 0.2 T. (a) What is the magnitude of the maximum induced emf in the coil? (b) How long does it take to complete one rotation? (c) What is the magnitude of the induced current at the instant that it completes half a rotation?

(a) (b) (c) (d) (e) ( into page) Loop moves at speed v toward north pole of magnet. Loop oscillates up and down between positions I and II. Loop falls over from position I to position II. Loop rotates about axis perpendicular to ends of magnet. Corners of loop are pulled until loop assumes shape II A current is induced in the square loop of wire in _______________________. A. situation a only B. situations a and e C. situations a, b, and e D. situations a, c, and e E. all situations except d F. all five situations

                                                  The rod above is conducting and can be slid left or right along a long U-shaped piece of bare high- resistance wire. The magnetic field is constant and directed into the screen. A constant current could be induced in the rod by sliding it ________________. A. at constant speed to the left B. at constant speed to the right C. with constant acceleration to the left D. with constant acceleration to the right E. at constant speed in either direction F. with constant acceleration in either direction