Beatty 6091_Electromagnetic induction_teacher

1 A) Faraday’s experiment Experiment to show that a changing magnetic field can induce an e.m.f. in a circuit 1. Set up the apparatus as shown in the diagram. 2. A permanent magnet is inserted into a solenoid connected to a sensitive galvanometer. 3. The galvanometer needle deflects as the permanent magnet move within the solenoid. 4. This shows that e.m.f. can be induced when there is a changing magnetic field. 5. This process is called electromagnetic induction. Note: Both e.m.f. and current are induced in a conducting wire when it is put in a changing magnetic field. So when e.m.f. is said to be induced in a coil, it should be understood that current is also induced at the same time. Definitions 1. Electromagnetic induction is the process through which an induced e.m.f is produced in a conductor due to a changing magnetic field. 2. Induced current is a current produced in a conducting wire due to changing magnetic field. Beatty Secondary School Secondary 4E Pure Physics Electromagnetic Induction Name: __________________________ ( ) Class: __________ Date: _____________ Learning Outcomes (a) deduce from Faraday’s experiments on electromagnetic induction or other appropriate experime nts: (i) that a changing magnetic field can induce an e.m.f. in a circuit (ii) that the direction of the induced e.m.f. opposes the change producing it (iii) the factors affecting the magnitude of the induced e.m.f. (b) describe a simple form of a.c. generator (rotating co il or rotating magnet) and the use of slip rings (where needed) (c) sketch a graph of voltage output against time for a simple a.c. generator (d) describe the use of a cathode -ray oscilloscope (c.r.o.) to display waveforms and to measure potential differences an d short intervals of time (detailed circuits, structure and operation of the c.r.o. are not required) (e) interpret c.r.o. displays of waveforms, potential differences and time intervals to solve related problems (f) describe the structure and principle of operati on of a simple iron -cored transformer as used for voltage transformations (g) recall and apply the equations VP / VS = NP / NS and VPIP = VSIS to new situations or to solve related problems (for an ideal transformer) (h) describe the energy loss in cables and deduce the advantages of high voltage transmission

2 Factors affecting the magnitude and direction of the induced e.m.f. Procedure Galvanometer response Insert North pole of 1 bar magnet into solenoid Insert North pole of 1 bar magnet into solenoid at twice the speed Insert North pole of 2 bar magnets into the solenoid Insert North pole of 1 bar magnet into a solenoid with twice the number of turns From the above process, we deduce that the strength or magnitude of the induced e.m.f. are affected by: 1. The speed with which the magnet is inserted into or withdrawn from t