Name: Teacher: Your Task As You Learn About the Discovery and Changes in the Understanding

Teacher:

Your task As you learn about the discovery and changes in the understanding of electromagnetic induction, you will see many interesting multimedia demonstrations and be able to use a series of flash activities. To help your understanding of this and many of the associated concepts, you should complete the exercises/tasks within each section. As a further aid to help increase your understanding of these areas it might be a good idea to complete this worksheet as an ongoing summary of your findings. You may use the following questions/tasks as a basis for your answer.

Faraday and induction What was one of Faraday’s earliest experiments in induction? What was the unexpected observation from this experiment? Explain what happens to a galvanometer needle in a circuit that is connected to a coil of wire when a bar magnet is pushed into it? If the magnet is removed from the coil of wire in the circuit above, what happens to the galvanometer needle?

Magnets and magnetic fields? If a magnetic field has strength (flux density) of 20 T and a surface area of 12 m2 calculate the total flux threading the object. Draw a table showing the magnetic fields around a bar magnet, horseshoe magnet and a rare earth disc magnet. Electric currents Explain why there is an induced current in a coil of wire when a magnet is pushed into the coil. Draw a table summarising the effects on the induced current in a circuit when each of the following variables is changed: 1. the distance between the coil and the magnet 2. the strength of the magnet is changed 3. the relative motion between the magnet and the coil is changed

Comparing experiments A bar magnet is pushed into a coil of wire. What is the relationship between the number of turns of wire in a coil and the current induced by this method? In the situation above, the bar magnet is removed. What is the effect on the magnitude and sign of the induced current? Explain the physical principles behind your answer.

A quick quiz Summarise the effect on a centre-zero galvanometer needle as a bar magnet is pushed into and out of a coil of wire. Lenz’s law After watching the multimedia video on back emf in motors, write a simple explanation of why the voltage and current readings changed. Analyse any risks in this experiment and say how you will minimise such risks. Compare the effectiveness of laminations made of plastic and those made of iron in an electric motor. Explain your response.

Eddy who? This time, explain how eddy currents produced the effects demonstrated in the multimedia video on electromagnetic braking. The two following questions refer the swinging metal sheets between the poles of a magnet Discuss the difference observed in the motion of the sheets with open and closed slots. Outline an experiment to compare the effectiveness of open/closed and no slots cut in a swinging sheet of metal between the poles of a magnet.

Electromagnetic braking Once again you have observed the effectiveness of eddy currents produced by the interaction of relative motion between a magnetic field and a metal. Draw a table to predict the results of dropping a single, very strong, rare earth magnet down vertical tubes made of copper, aluminium and plastic. (Very similar to the video) In each case, compare a tube with and without a vertical slot cut down its axis. Use the following as a reference point for your table. The time taken for a single bar magnet to fall 1.0 m from rest down a plastic tube is 0.45s. All tubes are the same length (1.00 m, diameter and thickness) As further consolidation of your knowledge of eddy currents and their applications, list how eddy currents are used in three (3) real world applications of electromagnetic braking. Applications For each of the following applications of induction describe briefly its operating principles. 1. induction furnaces 2. fluorescent light tubes 3. traffic lights 4. metal detectors 5. current / voltage detectors (light sabres) 6. stove cooktops.