Grade 12 - Transformers (Electrical Systems)

PRESCRIBED LEARNING OUTCOMES

• describe the operation of an electrical transformer
• describe the advantages and disadvantages of a core in a transformer
• describe the operation of an induction coil
• relate voltage in and voltage out to the number of windings in an electrical transformer
• determine input (primary) or output (secondary) voltage of a transformer, given the turn ratio
• determine input or output current for an ideal transformer, given the turn ratio
• describe situations that require step-up or step-down voltages
• explain why AC transmission systems are used rather than DC systems

SUGGESTED INSTRUCTIONAL STRATEGIES

• Have each student pass a current through a metal conductor placed near various items (e.g., radio, compass, tape player, TV) and note and record the effects. Then ask each student to use a coil and observe its effects on the same items. As a class, discuss observations and determine reasons for the results.
• Ask students to investigate the effect of cores on transformers. First each student winds a conductor around a pencil and determines how many paper clips can be lifted when a low voltage is applied. They then repeat the experiment, using iron nails instead of pencils, and relate their results to the operation of a transformer.
• Ask students, in groups or individually, to construct step-up or a step-down transformers using two concentric coils. First they measure the input and output voltage and compare the measured output voltage to the ideal output voltage. Then they insert iron rods and note the effect on the electrical advantage.
• Challenge students to identify transformers used locally. Included might be those in their homes, the school, and the community power grid system. A local hydro company representative might be called in to explain the step-up and step-down transformers used to send power from the power station to the school or homes.
• Ask students to research the possible effects of transformers and high voltage on human health. Ask them to consider the question: How has the construction of transformers changed in the last 50 years? Students could also research the construction of large transformers by the local hydro company and present their findings in reports or posters.

SUGGESTED ASSESSMENT STRATEGIES

• As students explain the voltage and windings relationship in transformers, look for evidence that they understand:
  • other relationships that can be determined
  • the magnetism-electricity relationship
  • calculations involving turn ratio and input and output voltages
• Ask students to prepare reports on the construction, operation, application, and maintenance of transformers. In assessing the reports, note how effectively they:
  • discuss electrical advantage
  • describe the relationship of construction to function
  • explain advantages and disadvantages of transformer applications
• Have students measure voltages, currents, and windings in transformer applications to confirm the calculated relationships between voltage and turn ratios. Note the extent to which students can:
  • use correct procedures to determine voltage and current
  • select and apply formulae in calculations
  • explain differences between calculated and measured values
• Have students describe in their journals the relationship between electromagnets and transformers. When assessing their responses, note the extent to which students are able to:
  • describe electromagnet and transformer construction
  • list and describe common applications of step-up and step-down transformers
  • explain voltage and turn ratios
  • indicate recognition of the significance of the core in transformers
  • demonstrate understanding of induction coil operation

RECOMMENDED LEARNING RESOURCES

Applications of Physics 11 and 12 develops an understanding of the concepts of physics through the design, construction, and use of a variety of devices. Although the resources listed below provide a range of teaching and learning opportunities in physics, none of them provide a comprehensive resources package that completely supports the philosophy and approach of the British Columbia curriculum in the applications of physics. Please see the Appendix B Introduction for further information.

Print Materials

• Cambridge Coordinated Science: Physics
• Heinemann Advanced Science: Physics

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Last Modified: April 1, 1998.
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