Key Learning Points:
1. Gravitational potential energy
2. Motion under gravity
3. Conservation of energy
4. Magnetic force and magnetic field
5. Electromagnetic induction
6. Making models and experimentation skills
7. Self learning
Although hydroelectric power plants are large-scale projects, the basic working principle of a hydroelectric turbine generator can be demonstrated by a simple model. Everyday materials such as plastic bottles, cardboard, copper wires, and plastic spoons, can be used to construct a simple model of a hydroelectric turbine generator like the one below.
|A small model of hydroelectric turbine generator.
||See the enlarged rotor-stator part of the generator. As water pushes the turbine, the magnets (rotor) are rotated around the coils (stator) to generate electricity.
To design a hydroelectric turbine generator model, you can use the knowledge on electromagnetic induction that you learnt in your physics lessons and access the wealth of information on the construction of a hydroelectric turbine generator model available in books and on the Internet. With this information and a little ingenuity, you can construct a hydroelectric turbine generator model that generates a decent output voltage!
To design and construct a hydroelectric turbine generator model which produces the highest output voltage compared to that of your classmates' models.
- Reviewing physics principles of electromagnetic induction
Electricity is generated when a conducting coil is in motion in a magnetic field. The emf induced in the coil increases with the rate of change of magnetic flux through the coil. The induced emf can therefore be increased by
- increasing with the rotational speed of the turbine
- increasing the number of turns in the coil
- increasing the strength of the magnetic field
- inserting an iron core inside the coil to increase the magnetic flux passing through the coil
- using a larger coil to enclose more magnetic flux
- Design the model
You will be divided into groups of 4-5 students. Each group is to design and construct a hydroelectric turbine generator model using water from a running tap as the source of energy. Besides the knowledge of electromagnetic induction, you should also consider other factors that affect the efficiency of the generator, for example, how to reduce friction on the moving parts, and how to make turbines that can be effectively rotated by running water. You should also decide whether your model will output an AC or DC voltage.
Information on the construction of hydroelectric turbine generator model can be found in books and on the Internet. You should use simple everyday materials if possible and use waterproof materials for the parts that will come into contact with water. The following things should also be considered:
Notes to teachers: Remind students to ensure safety during the construction process. Take care when using tools and sharp instruments.
- Is the output voltage of your model going to be AC or DC?
- Are you going to use a ready-made generator or construct your own generator from materials like wires and magnets?
- If you decide to construct your own generator, how should the coils be wound?
- How should the magnets be oriented to increase the flux linkage?
- How will the water reach the turbine and how will it leave? How effectively will the turbine rotate in running water?
- How can the output voltage of the model be easily measured by a multimeter?
- After you have constructed the model, connect the model to a multimeter and switch on the multimeter to measure the output voltage (AC or DC).
- Place the model at a fixed height under a running tap releasing a fixed amount of water. Measure and record the voltage reading from the multimeter.
- The group that obtains the highest voltage reading will win this part of the competition.
Now place the model under the running tap at various height differences. Connect a long rubber tube to the tap if necessary to increase the range of height differences.
- Record the height difference and the corresponding voltage reading. State the two points between which the height difference is measured.
- What does the height difference represent in a real hydroelectric power plant?
- How is the height difference related to the output voltage readings? Explain the relationship using your knowledge of mechanics: acceleration under gravity, transfer of momentum, etc. You may need to make reasonable assumptions in your explanation.
- Vary the amount of water released from the tap from small to large. Measure and record the output voltage for the different quantities of water released. Try to explain the readings obtained.
- If time allows, vary the following to see how the output voltage changes:
Try to explain the outcomes.
- The strength of the magnet
- The number of turns in each coil
- Insert or remove iron core from the coil
Write a report about your hydroelectric turbine generator model. In your report, you should
- discuss the features you used in your design, especially those that make the induced emf higher, and explain the physics behind these features.
- present the data obtained from your experiment along with an explanation of the outcomes.
- demonstrate your knowledge of physics, especially in mechanics, electricity and magnetism.
The teacher will grade each report according to how well the above criteria have been addressed. Based on the output voltages obtained from each model, and the quality of each report, an overall winner will be chosen.