Datalogging in Science

Generating Electricity (a.c.)

Overview
In this experiment we investigate how alternating current (a.c.) may be generated. A magnet is set spinning inside a coil and the current induced by this action is detected by a current sensor. A graph of current versus time is plotted by the datalogging system.

Apparatus
1. A Datalogger.
2. A Current sensor (100 mA), or Voltage sensor.
3. A suitable coil of wire (e.g. Helmholtz coils)
4. A strong bar magnet.
5. Rubber bands.
6. Retort stand and boss.

Procedure
1. Assemble the apparatus as shown in the diagram above; the magnet is suspended by a thin cord or elastic band.
2. Connect the Current Sensor (100mA) to the datalogger.
3. Check that the magnet can spin freely within the centre of the coil.
4. Set the datalogging software to record current in Real time.
5. Rotate the magnet 20 or 30 times so as the cord is well twisted and hold it until ready.
6. Start recording and release the magnet. If the magnet touches the sides of the coil you will need to adjust the magnet’s position and restart.
7. Save the results before analyzing them.

Results
Analyze the graph to see that the current is alternating.
Explore the factors affecting the magnitude of the current generated.
Label the start and finish of one complete cycle.
Use the analysis features of the software to find the biggest voltage created and the time taken for 5 complete cycles
Measure the frequency of the a.c. at a number of stages in the observation period.

Questions
1. What was the maximum value of current?
2. How was the current related to the speed of rotation of the magnet?
3. How many revolutions did the magnet make? Explain your answer?
4.Mains Electricity changes from positive to negative 50 times per second. Using your value for the time of 5 cycles calculate the cycles per second of the experiment. Use the unit Hz (Hertz), not cycles per second.
5. Why is mains electricity alternating (a.c.)?

Extensions
1. What is the difference between a generator and an alternator?
2. Research the work of Michael Faraday and produce a simplified set of his laws.

Data Harvest users

1. Connect the sensor to the datalogger and the logger to the computer
2. Then click the Set Up icon to the right of this message.
3. When the software opens, click the Play button.