Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Generators and Alternating Current • A generator converts mechanical energy into electrical energy by induction. • A generator produced a continuously changing emf. • The induced emf alternates in sinusoidal manner between maxima. • This variety of current is called alternating current, or AC Maximum emf for a generator emf max = NABω emfmax = Max. induced emf N = # of loops How quickly loops are spinning A = cross-section area of loops B = magnetic field strength ω = angular speed of loops Maximum emf for a generator Sometimes the frequency of spin is given instead of angular speed. 2π f = Angular distance 1 sec →ω Maximum emf for a generator (equation 2) emf max = NAB(2πf ) emfmax = Max. induced emf N = # of loops A = cross-section area of loops B = magnetic field strength Angular speed f = frequency of spin 1 Mutual Inductance • Mutual inductance is a measure of the ability of one circuit carrying a changing current to induce an emf in a nearby circuit. • The coil carrying the current initially is called the primary coil. • The coil in which the current is induced is called the secondary coil. Transformers • Transformers are devices that change one AC potential difference to a diferent AC potential difference. • Real transformers are not perfectly efficient. – Efficiencies of real transformers typically range from 90% to 99%. • For this class, we will assume 100% efficiency. (We like living in an ideal world) :) Residential Power Poles usually have 3 levels of wires. High Voltage 120 –240 Volts Telephone-Cable TV Transformer Transformers Transformers Transformers can change the voltage, either up or down. primary volts secondary volts = # primary coils # secondary coils Volts x amps = Volts x amps in out 2 Transformer Equation ΔV2 ΔV1 = N2 N1 Where ΔV = potential difference N = # of turns in coil Subscript 1 refers to primary coil Subscript 2 refers to secondary coil Example: A step up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary has 75 turns, how many turns must the secondary have? ΔV2 ΔV1 = N2 N1 2400 120 = 75 N2 V1 = 120 V V2 = 2400 V N1 = 75 turns N2 = ? N2 = 1500 turns Power for a transformer • The power into a transformer equal the power out of a transformer P1 = P2 • To determine the power, use the current: P = IV 3