Energy Transformation
In 2017, Tesla installed a 100 MW battery in South Australia that converts stored electrical energy to grid power in under 140 milliseconds — 70 times faster than a gas power plant can respond.
Printable Worksheets
Print or save as PDF — or build a custom worksheet from any module's questions.
Q1 · A torch converts chemical energy (battery) to light. But the torch also gets warm. Where does the heat come from?
Q2 · A petrol car engine converts chemical energy to motion. About 70–75% is wasted as heat. Is that acceptable — and why might electric cars be better?
● Know
- That energy transformation is a change from one form to another
- That energy is never created or destroyed (conservation of energy)
- "Lost" energy almost always becomes heat or sound
● Understand
- How to draw and read energy transformation diagrams (chains)
- What efficiency means and how to calculate it as a percentage
- Why no device is 100% efficient
● Can do
- Draw an energy transformation chain for a common device
- Calculate efficiency given input and useful output energy
- Trace the full energy chain from power station to light bulb
When a battery-powered torch is switched on, energy in the battery is converted to energy, which flows to the bulb. The bulb converts this to energy (useful output) and energy (waste). According to the law of of energy, no energy is created or destroyed.
Hold your phone for a few seconds after watching a video: it is warm. Your phone just converted electrical energy into light, sound — and heat you can feel with your fingers. Nothing was "used up"; the energy just changed form. Your body does the same thing: the chemical energy in your breakfast has turned into movement, warmth, and sound (your voice) right now.
Energy transformation diagrams (energy chains) use arrows to show each step:
| Device | Input energy | Useful output | Waste |
|---|---|---|---|
| Torch (LED) | Chemical (battery) | Light | Heat (small) |
| Electric motor | Electrical | Kinetic (mechanical) | Heat, Sound |
| Petrol engine | Chemical (petrol) | Kinetic | Heat (large), Sound |
| Solar panel | Radiant (light) | Electrical | Heat |
| Human muscle | Chemical (food/glucose) | Kinetic | Heat (body warmth) |
Notation for a torch: Chemical energy [battery] → Electrical energy → [LED bulb] → Light energy + Heat energy (waste)
Always identify: (1) the input energy, (2) the useful output, (3) the waste energy. The waste usually goes to heat or sound.
energy enters the hair dryer. The heating element converts it to energy (heat). The fan motor converts electrical energy to energy to blow the air. Some energy is also wasted as (the noise of the motor and air). All waste energy ultimately becomes .
When energy "disappears", it almost always goes to heat or sound. It isn't destroyed — it's just in a form that's hard to reuse. This is why no device is 100% efficient.
Efficiency formula:
Efficiency (%) = (Useful energy output ÷ Total energy input) × 100
| Device | Efficiency (approx.) | What happens to the rest? |
|---|---|---|
| Incandescent light bulb | ~5% | 95% becomes heat (very hot to touch) |
| LED light bulb | ~85–90% | 10–15% becomes heat (barely warm) |
| Petrol car engine | ~25% | 75% goes to heat (exhaust, engine block, friction) |
| Electric motor (EV) | ~85–95% | 5–15% to heat |
| Human muscles | ~25% | 75% becomes body heat |
This is why LED bulbs have replaced incandescent bulbs across Australia — switching from 5% to 90% efficiency saves enormous amounts of electricity. The waste heat from incandescent bulbs used to add to summer cooling costs too.
Understanding energy chains helps us evaluate our power systems. Here are two Australian examples:
Coal-fired power station (e.g. Loy Yang, Victoria):
Chemical energy (coal) → Thermal energy (burning → steam) → Kinetic energy (steam turbine) → Electrical energy (generator) → [transmission lines] → Electrical energy (home) → Light + Heat (bulb)
Each arrow loses some energy. By the time light reaches your home, roughly only 30–35% of the original coal's chemical energy has become useful light.
Solar farm (e.g. Sunraysia Solar Farm, NSW):
Radiant energy (sunlight) → Electrical energy (solar panel) → [transmission] → Electrical energy (home) → Light + Heat
Solar panels are ~20% efficient at converting sunlight to electricity, but the "input" (sunlight) is free and produces no greenhouse gases.
Snowy 2.0 pumped hydro — an energy "battery":
Surplus electrical energy → Kinetic energy (pump) → Gravitational PE (water pumped uphill) [stored] → KE (water flowing down) → Electrical energy (generator) → homes
This is how Australia stores renewable energy for when the sun and wind aren't producing — by converting electrical energy to stored GPE and back again.
A petrol car engine uses 1000 J of chemical energy from fuel but only delivers about 250 J to the wheels as kinetic energy. Predict: where does the other 750 J go? Why is it physically impossible for an engine to be 100% efficient?
How close was your prediction?
Earlier you were asked: A petrol car engine converts chemical energy to motion. About 70–75% is wasted as heat. Is that acceptable — and why might electric cars be better?
Now that you've worked through the lesson, write a fuller answer. Use the words efficiency, waste energy, and conservation of energy at least once each.
Q1. Draw and describe an energy transformation diagram for a hair dryer. Identify the input energy, useful output, and waste energy. (3 marks)
Q2. A petrol engine uses 1000 J of chemical energy and produces 250 J of kinetic energy. Calculate the efficiency and explain what happens to the remaining 750 J. (3 marks)
Q3. Compare the energy transformation chains for a coal-fired power station and a solar farm generating the same amount of electricity. Suggest one advantage and one disadvantage of each. (5 marks)
Answers
▾MCQ 1
C — A burning candle converts chemical energy (wax + wick) to both light and heat. Most of the energy actually becomes heat; the light is the visible component. Both outputs exist simultaneously.
MCQ 2
B — An electric motor's main purpose is to produce motion (kinetic energy) from electricity. Some energy is always wasted as heat (friction in bearings, resistance in coils) and a little as sound.
MCQ 3
C — Efficiency = (2 ÷ 10) × 100 = 20%. The other 8 J becomes heat (waste). This is better than a traditional incandescent bulb but still not perfect.
MCQ 4
B — Conservation of energy means the total stays the same. The heat is "lost" from the useful output point of view — it dissipates into the surroundings — but it still exists as thermal energy in the environment. It cannot be destroyed.
MCQ 5
B — A car engine burns petrol (chemical energy) and converts it to kinetic energy (motion of the car) plus large amounts of heat. Solar panels convert radiant to electrical (not kinetic). Wind turbines convert kinetic to electrical. Dams convert GPE to kinetic to electrical.
Short Answer 1
Model answer: Electrical energy [plug] → Hair dryer → Thermal energy (heat from heating element) + Kinetic energy (fan blows hot air) + Sound energy (motor noise, waste). The input is electrical energy. The useful outputs are thermal energy (to dry hair) and kinetic energy (moving air). The waste is mainly sound from the motor. A small amount of electrical resistance in the wires also becomes heat waste.
Short Answer 2
Model answer: Efficiency = (250 ÷ 1000) × 100 = 25%. The remaining 750 J is not destroyed — conservation of energy means it must still exist. It is mainly converted to thermal energy (heat) in the engine block, exhaust gases, and friction in moving parts. Some becomes sound energy (engine noise). The heat dissipates into the environment and cannot easily be reused, which is why petrol engines are described as inefficient.
Short Answer 3
Model answer: Coal chain: Chemical (coal) → Thermal (steam) → Kinetic (turbine) → Electrical → [transmission losses] → Electrical (home). Solar chain: Radiant (sunlight) → Electrical (panel) → [transmission] → Electrical (home). Coal advantage: reliable 24/7 output, not weather-dependent; disadvantage: burns fossil fuels → CO₂ emissions, contributing to climate change. Solar advantage: zero emissions during operation, free fuel (sunlight); disadvantage: only generates during daylight (not at night) and output varies with cloud cover — needs storage to be reliable.