Year 9 Science · Unit 3 · Lesson 14
Foundation Worksheet
Learning Goals
Match each part of the grid to its job
Write the letter of the matching job in the middle column. Each letter is used once.
| Part of the grid | Letter | Job |
|---|---|---|
| Generator | A. Carries electricity at very high voltage over long distances | |
| Step-up transformer | B. Lowers the voltage from transmission levels to distribution levels, then to the level used in homes | |
| Transmission line | C. Carries electricity at lower voltage through local streets to homes and businesses | |
| Step-down transformer | D. Changes kinetic energy into electrical energy at the power station | |
| Distribution network | E. The organisation that balances supply and demand across the National Electricity Market | |
| AEMO | F. Raises the voltage from generation levels to transmission levels |
1. What does a transformer do? Name the two kinds of transformer on the grid, and say where each one is found.
Fill the gap
Choose the correct word from the word bank. Each word is used once. Two words will not be used.
At a power station, a step-up raises the to hundreds of thousands of volts. For the same power, this lowers the in the wires. Because the power in a wire depends on the current squared (P = I²R), a smaller current greatly reduces the energy wasted as heat during . The (National Electricity Market) links Queensland, New South Wales, Victoria, South Australia and Tasmania. The (Australian Energy Market Operator) keeps supply and demand balanced at every moment.
2. A power station sends out 66 MW (66,000,000 W) of electrical power. Use I = P ÷ V to calculate the current in the wires (a) at 22,000 V and (b) after a step-up transformer raises the voltage to 330,000 V. (c) How many times smaller is the current?
(a) Current at 22,000 V A
(b) Current at 330,000 V A
(c) Smaller by times
Investigation: a model power line
A class used a model power line kit. The same power, 12 W, was sent along the same thin wires at three different voltages. The class measured the power lost as heat in the wires.
| Voltage (V) | Current, I = P ÷ V (A) | Power lost as heat in the wires (W) | Percentage of the 12 W lost (%) |
|---|---|---|---|
| 6 | 2.0 | 0.80 | 6.7 |
| 12 | 0.20 | ||
| 24 | 0.05 |
Source: sample class results.
3. Fill in the current and the share of the power lost for the 12 V and 24 V trials. Give the shares to one decimal place.
4. Describe what happened to the current and to the power lost each time the voltage doubled. Use P = I²R to explain the pattern in the power lost.
Scenario: from a wind farm to a school
A wind farm on the Southern Tablelands of NSW sends electricity about 250 km to schools and homes in Sydney. Along the way, the electricity passes through several transformers.
5. Explain why the grid needs a step-up transformer near the wind farm AND step-down transformers near the school. Describe the voltage at each stage of the journey.