C-3 Generators and Faraday’s Law of Induction

1 Faraday’s law of induction

There are no questions to answer in Part 1

2 Investigating the generator

a. Slowly shake a permanent magnet back and forth very close to the coil. Watch the multimeter. What do you notice?

b. Shake the magnet at a faster rate. What happens to the voltage?

c. Slowly move the permanent magnet away from the coil, and continue to shake it at the fast rate. What happens to the voltage?

d. Place the magnet on the coil. What is the voltage created when the magnet is not moving?

3 Building the generator

There are no questions to answer in Part 3

4 Gathering Data

Table I: Generator Data with Alternating Magnetic Poles Facing Out

Rotation Frequency / Voltage with 2 magnets / Voltage with 4 magnets / Voltage with 6 magnets / Voltage with 12 magnets
40 Hz
60 Hz
80 Hz

Table II: Generator Data with North Poles Facing Out

Rotation Frequency / Voltage with 2 magnets / Voltage with 4 magnets / Voltage with 6 magnets / Voltage with 12 magnets
40 Hz
60 Hz
80 Hz

Table III: Generator Data with South Poles Facing Out

Rotation Frequency / Voltage with 2 magnets / Voltage with 4 magnets / Voltage with 6 magnets / Voltage with 12 magnets
40 Hz
60 Hz
80 Hz

5 Analyzing the data for the alternating poles generator

a. Use the data from Table I to make a graph of voltage vs. number of magnets for each frequency. Plot all three sets of data on the graph below. Use three separate colors, one for each frequency. Label each line.

b. How does changing the number of magnets affect the voltage generated? If you double the number of magnets, how much does the voltage change?

c. Suppose you had a rotor with a different magnet slot spacing. If you used 9 magnets, what would you expect the voltage to be for each frequency? You should use your graph to answer this question.

d. How does increasing the speed of the rotor turns affect the voltage generated? If you double the speed, how much does the voltage change? You should mention Faraday’s law in your answer.

e. Why is it important for the generator coil to be positioned close to the rotor? If you loosen the generator coil screws and slide it away from the motor, what happens to the voltage generated?

6 Analyzing the data for the non-alternating poles generator

a. Use the data from Table II to make a graph of voltage vs. number of magnets for each frequency. Plot all of the data on the same graph, using different colors, and label the frequency of each line.

b. Compare the voltage generated with north poles facing out to the voltage of the generator with alternating poles facing out. Examine the data closely. Which design produced the greater voltage overall?

c. Is the difference between the voltage of the two generator designs more noticeable at low or high speeds? Why do you think this is?

d. Compare the voltage created by each design using 12 magnets. Why do you think the generator with all north poles facing out did not work well with 12 magnets?

e. Compare the data in Table II and Table III. What do you notice?

7 Applying what you have learned

a. A typical AA, C, or D battery has a voltage of 1.5 volts. How does the maximum voltage of the generator compare with the voltage of a battery?

b. How could you improve the design of the generator? Discuss three improvements you could make that would increase the voltage generated.

c. A bicycle light generator is a device that is placed on the wheel of a bicycle. When the wheel spins, the generator powers the light. Explain how you think this type of generator works? What is one drawback to using this type of light on a bike?

Questions

a. What is the difference between a motor and a generator?

b. What type of current does the generator create?

c. What is the name of the process through which the generator creates electricity? Explain this process.

d. State Faraday’s law of induction and explain how it relates to the electric generator.

e. A generator with alternating magnets is spinning at 25 rpm and produces a voltage of 0.10 volts. How fast must it be spun to produce a voltage of 0.20 V?