MOTORS AND GENERATORS

Transcription

1 MOTORS AND GENERATORS HSC KICKSTART PHYSICS WORKSHOP LIST OF EXPERIMENTS 1. The Motor Effect 2. Electromagnetic Induction and Lenz s Law 3. Generators 4. Transformers 5. AC Induction Motors Name: Kickstart would like to acknowledge and pay respect to the traditional owners of the land the Gadigal people of the Eora Nation. It is upon their ancestral lands that the University of Sydney is built. As we share our own knowledge, teaching, learning, and research practices within this University may we also pay respect to the knowledge embedded forever within the Aboriginal Custodianship of Country.

2 The University of Sydney The Motor Effect An electric charge experiences a force when it moves in a magnetic field. Thus, a current-carrying conductor feels a force from a magnetic field. This is the motor effect. B field into page force path of positively charged particle velocity A Working Motor Label the parts of the motor on the pictures below. Are these DC motors or AC? Or both? How can you tell?

3 Galvanometer Features: Characteristics: Describe the application of the motor effect in a galvanometer. Loudspeaker Features: Characteristics: Describe the application of the motor effect in a loudspeaker.

4 Electromagnetic Induction and Lenz s Law Using the Predict, Observe, Explain model of scientific enquiry, examine these 5 experiments to synthesise the information into a description of Lenz s Law. Magnet and coil The wire coil is connected to a galvanometer that measures small amounts of current. What happens when you move the magnet faster? What happens when you use the weaker (smaller) magnet? When you bring the magnet s north pole towards the coil, can you tell which way the induced current flows in the coil? How? Predict Observe Explain Falling magnets You have a very strong magnet a neodymium magnet and some tubes. Drop the magnet down the tubes and observe how long it takes for the magnet to reach the bottom of each tube. The magnet falls slower in the copper tube than in the PVC pipe. Why? Predict Observe Explain Jumping rings Why do the rings jump into the air? Which ones don t work and why? Predict Observe Explain

5 Pendulum Three different pendulums can be swung between the poles of the permanent magnet. Try each one in turn and observe how long they swing before stopping. Where is the stopping force coming from? How can this be used in electromagnetic braking? Predict Observe Explain Arago s Disk Turn the magnets past the disk. The disk will move too. What is the disk made of? Is it magnetic? Why does the disk spin? Predict Observe Explain Lenz s Law There are 4 parts to Lenz s Law. 1. A changing induces a 2. that gives rise to an 3. force that 4. the original change.

6 Generators AC/DC Generator How can you tell if the generator is producing AC or DC electricity? Draw the output of the generator as viewed on the CRO screen for both AC and DC Predicted Observed Predicted Observed

7 Twelve-phase generator What kind of commutator does the twelve-phase generator have? Predict and draw what you think the output of the generator would look like on the CRO: Predicted Observed

8 Transformers Transformers use the ideas of electromagnetic induction to transform one voltage into another. The number of turns in the primary and secondary coils is the crucial point here, since the ratio of the primary voltage to the secondary voltage is V p /V s = n p /n s That is, if the number of turns in the secondary coil is increased, the voltage output of the secondary coil is increased. DIY transformer Primary n p = Secondary n s = V p = So we should get V s = Compare your prediction to the actual value by using a multimeter: V s = Does the predicted value match the measured value? What reasons can you give as to why our measurement might be different to the calculated value? Explain how this effect is used for transmission of electricity from power stations t our homes. Cause: Effect: Relationship between Why/How

9 AC Induction Motors The parts of the squirrel-cage rotor are: Constuct from the parts provided, a working AC induction motor. Different types of motors Different types of motors have different components. Fill in the table below for each type of motor. Description Component DC motor Universal Motor AC Induction motor Rotor Stator Commutator Power supply Physics concept behind motor Applications/ Examples

10 Generate some motor-vation If you listen closely throughout the workshop, the demonstrators might let some of this info slip, but if not, just ask them. Write an interesting fact you learnt about Physics List three risks in the 2 nd year lab Risk Consequence Precaution Find and list the 4 famous scientists in the lab. Careers with Your demonstrator might be able to help with this What sort of career do you think you could get if you studied this topic at the University of Sydney? Industry Research Public service

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