Ch22_RabinR

= Chapter 22: Induced Voltage and Inductance = toc //These two websites are excellent resources for notes and sample problems appropriate for AP level: [] and []//

Guiding Questions #1-3
1. What happens when you move a magnet near a coil of wire? By putting a magnet near a coil of wire one induces current. The magnet and coil of wire now act as if two magnets are being held near each other. They can attract or repel based on the directions of the electric field lines and current. 2. What happens when you hold the magnet stationary near a coil of wire? When you hold a magnet stationary near a coil of wire there is no current and therefore there is no magnetic attraction. 3. When is //emf// induced? (3 situations) 3 ways to induce //emf// is changing the angle, changing the area, or changing the field strength.

Guiding Questions #4-8
4. What is Faraday's law of induction? Faraday's law of induction states that the emf can be induced in a loop if magnitude flux is change. The rate of change is the major influence on the amount of induced emf. 5. Why is the expression for Faraday’s Law negative? The negative is included in the expression of Faraday's law due to the rule that the magnetic field always opposes the flux of the primary object. This is stated in Lenz law. 6. What is Lenz’s Law? Lenz law starts that the induced emf generates a current that set up its won magnetic field. The magnetic field acts to oppose the change in flux. 7. //Consider a flat square coil with N = 5 loops. The coil is 20 cm on each side, and has a magnetic field of 0.3 T passing through it. The plane of the coil is perpendicular to the magnetic field: the field points out of the page.// a) If nothing is changed, what is the induced emf? emf = 0 b) The magnetic field is increased uniformly from 0.3 T to 0.8 T in 1.0 seconds. While the change is taking place, what is the induced emf in the coil? E = n(flux/t) E = 5(.5*.2*.2/1) E = .1 V c) While the magnetic field is changing, the emf induced in the coil causes a current to flow. Does the current flow clockwise or counter-clockwise around the coil? Bp = out Increase Flux p = out Flux s = in Bs = in clockwise 8. Check out: [|**http://micro.magnet.fsu.edu/electromag/java/lenzlaw/index.html**]. Record your observations.

Virtual Laboratory
Electromagnetic Induction Date: 12/6/2011

HYPOTHESIS To induce a current in a loop of wire a magnet must be brought in close distance to a coil of wire. The three facts that influence the direction and magnitude of the induced current are changing the angle, changing the area, and changing the field strength.



DISCUSSION QUESTIONS 1. Based on your observations from the first part of the lab, did the speed of the motion have any effect on the galvanometer? Yes the manner in which the galvanometer indicator needle responds or deflects depends on the manner in which the magnet or coil of wire moves. Therefore the faster the magnet or coil of wire moves, the faster the galvanometer will respond. 2. In the first part of the lab, did it make a difference whether the coil or the magnet moved? It did not make a difference whether the coil or the magnet was moved. In both cases, the voltage meter had the same reaction. 3. Explain what the voltage meter readings revealed to you about the magnet and the wire coil. The angular rotation of the voltage meter is proportional to the current through the coil. 4. Based on your observations, what conditions are required to induce a current in a circuit? This experiment shows that to induce current in circuits one must bring a magnet near a coil of wire. The experimenter can also bring a coil of wire near a magnet. In each situation the results will not be affected. 5. Based on your observations, what factors influence the direction and magnitude of the induced current? The factors in which influence the direction and magnitude of the induced current include the angle, the field strength, and the area.

Guiding Questions #9-17
9. __Why__ is an //emf// induced between the ends of a rod moving in a magnetic field? When a rod moves in a field, you induce current and therefore when current is induced, emf is induced as well. 10. What is motional //emf//? Motional emf is the result of the previous example. The equation for motional emf is emf = vBl. 11. When is motional //emf// largest? Motional emf is largest when the rod and magnetic field are perpendicular to each other. 12. What happens if the metal rod is part of a complete circuit? When a metal rod is part of a complete circuit 13. Derive the equation: V = Bl//v// //E = flux/ time// //E = NBA / t// //E = Blw/t// //E = Blv// 14. Why is an electric field produced when a conducting rod is moved in a magnetic field? When a conducting rod is moved in a magnetic field a current is induced in the circuit. Whenever current is induced it means there must be an electric field in the circuit. 15. How is the concept of motional //emf// consistent with Faraday’s Law? Faraday's law states that only when there is a change in flux can the current be induced. Motion emf is consistent because the equation will equal zero every time unless there is a change in flux. 16. The sliding bar has a length of 0.50 m and moves at 2.0 m/s in a magnetic field of magnitude 0.25 T. (a) Find the induced voltage in the moving rod. (b) If a 0.50 W resistor was placed in the circuit, what would the current b? (c) What force must be applied to the rod to keep it moving at constant speed? a) V = Blv V = .25*.5*2 V=.25 V

b) V = IR .25 = I*.5 I = .5 A

c) F = BILsintheta F = .25*.5*.5sin90 F = .063 N 17. See animation: http://www.ngsir.netfirms.com/english/induction.htm **Record your observations.**