April 5 th 2011

 Electric Generator : converts mechanical energy to electric energy.  Consists of numerous loops of wire placed in a strong magnetic field with the wire being wound around an iron form to increase the strength of the magnetic field.  The wire and iron are called the armature.... Think of the electric motor.

 Armature is mounted so it can rotate freely in the field, as the armature turns the wire loops cut through the magnetic field lines inducing an EMF.  When a generator is connected in a closed circuit; the current flow is proportional to the EMF.  Use third RHR to determine the direction of the current.

 As the loop rotates, the strength and direction of the current change with the current being greatest when the motion of the loop is perpendicular to the magnetic field – loop is in the horizontal position.  When the loop is parallel to the field – current is zero.

 As the loop continues to turn, the segment that was moving up begins to move down, reversing the direction of the current in the loop. This change in direction occurs each time the loop turns through 180°.

 An energy source turns the armature of a generator in a magnetic field at a fixed number of revolutions per second. i.e 60 Hz – the current goes from one direction to the other and back 60 times per second.  The following diagram shows how an alternating current in an armature is transmitted to the rest of the circuit.

 AC Generator AC Generator  If the armature turns fast enough, the light does not appear to dim or brighten due to the speed at which it occurs.

 The power produced by a generator is the product of the current and the voltage.  Power always being positive because either both voltage and current are either negative or positive. *have to be the same*  Because I and V vary, the power associated with an alternating current varies and its average value is less than the power supplied by a DC with the same V max and I max.

 The average AC power is P AC = (½)P ACmax = (½) P DC The voltage generally available at wall outlets is described as 120V, where 120 is the effective voltage. Formulas for calculating V eff and I eff V eff = V max I eff = I max

 An AC generator develops a maximum voltage of 34V and delivers a maximum current of 0.17A to a circuit. a) What is the effective voltage of the generator? b) What effective current is delivered to the circuit? c) What is the resistance of the circuit? V max = 34V, I max = 0.17A

a) V eff = 0.707V(V max ) = 0.707V(34V) = 24V b) I eff = 0.707V(I max ) = 0.707V(0.17A) = 0.12A c) R = V eff / I eff = 24V/0.12A = 200 Ω = 2.0 x 10 2 Ω

 Pg. 798 # 6  Read Pgs : Compare and contrast AC & DC Generators. Write in your own words a definition and explanation for the following terms. AC Generator, Slip-ring Commutator, DC Generator and rectified DC Current.