1 / 21

Chapter 22 Induction & Alternating Current

Chapter 22 Induction & Alternating Current. Section 1 Induced Current. Magnetism vs. Electric Current. Oersted : An electric current produces a magnetic field Oersted Experiment Faraday: A magnetic field produces an electric current = electromagnetic induction

yale
Download Presentation

Chapter 22 Induction & Alternating Current

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 22 Induction & Alternating Current Section 1 Induced Current

  2. Magnetism vs. Electric Current • Oersted: An electric current produces a magnetic field • Oersted Experiment • Faraday: A magnetic field produces an electric current = electromagnetic induction • Either by moving the conductor (=wire) or the magnets

  3. Electromagnetic Induction (2 min)

  4. 4th Right-Hand Rule • Predicts the direction of current produced in a magnetic field *Current is made of positive charge particles.

  5. All Right-Hand Rules *The following rules are for an open palm.

  6. Faraday’s Law • Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. • EMF = electromotive (or electromagnetic) force • Not a force, but a potential (energy) difference = voltage = E/q • V=IR for a current flowing through a resistor • The changes could be:(1) changing the magnetic field strength (2) moving a magnet toward or away from the coil, (3) moving the coil into or out of the magnetic field, (4)rotating the coil relative to the magnet, etc.

  7. EMF

  8. Sample Problem 22A A coil with 25 turns is wrapped around a hollow tube with an area of 1.8 m2. Each turn has the same area as the tube. A uniform magnetic field is applied to a right angle to the plane of the coil. If the field increases uniformly from 0.00 T to 0.55 T in 0.85 sec, find (1) the magnitude of the induced emf in the coil. If the resistance in the coil is 2.5 Ω, fid the magnitude of the induced current in the coil.

  9. Induced EMF • Test charge, q in the wire is moved to right (= thumb) in a uniform magnetic field (= fingers) • Magnetic force (palm) produced moves the charged particles in the wire • Flow of charged particles = current • Current replaces magnetic force • Current flows only if there is a wire

  10. Induced EMF • Don’t be misled by the letter F, EMF is not a force • EMF = BLvsinө • B = strength of magnetic field (tesla) • L = length of wire in the magnetic field (meter) • v = velocity of wire (meter/sec) • ө = angle between the magnetic field and the direction of wire moving (degrees)

  11. Example A straight wire, 0.20 m long, moves at a constant speed of 7.0 m/s perpendicular to a magnetic field of strength 8.0×10-2 T. • What EMF is induced in the wire? • The wire is part of a circuit has a resistance of 0.50 Ω. What is the current through the wire? • If a different metal is used for the wire, which has a resistance of 0.78 Ω, what would the new current be?

  12. Applications of Induced Current • AC Generator • How does AC generator work? (12 min) • Microphone • How do microphones work? (5 min)

  13. AC Generator current flow

  14. AC Generator • Current vs. time • Voltage vs. time

  15. Maximum EMF for a Generator • emfmax = NABω • N = number of loops • A = cross-section of loops • B = magnetic field strength • ω = angular frequency of loops (how many radians per second = angular speed) = 2πf (f = frequency = cycles per second) • Compare to Faraday’s law of induction

  16. Sample Problem, 22B A generator consists of exactly eight turns of wire, each with an area A=0.095 m2 and a total resistance of 12Ω. The loop rotates in a magnetic field of 0.55 T at a constant frequency of 60.0 Hz. Find the maximum induced emf and maximum induced current in the loop.

  17. Average Power of AC average voltage average current P = IV average power Paverage = ½ Pmax

  18. Root-mean-square (RMS)

  19. Effective Current, Ieff • Applies to AC • ≈ average current • Ieff = Irms • Combine Paverage = (Ieff)2R, Paverage= ½ Pmax, and Pmax=(Imax)2R to derive:

  20. Effective Voltage, Veff • Combine Veff = Ieff R and Ieff = 0.707∙Imax , derive: Veff = 0.707Vmax • Veff = Vrms

  21. Sample Problem 22C A generator with a maximum output emf of 205 V is connected to a 115 Ω resistor. Calculate the rms potential difference. Find the rms current through the resistor. Find the maximum AC current in the current.

More Related