What is energy?
Energy is the ability to do work or cause change. It can exist in many forms such as heat, light, motion, and electricity.
What are the two main types of energy? give examples
Kinetic energy – energy of movement (e.g. moving car, flowing water).
Potential energy – stored energy that can be released (e.g. stretched rubber band, object held high).
Give examples of each type. Kinetic energy and Potential energy
Kinetic energy: moving ball, sound waves, wind.
Potential energy: gravitational potential (height), elastic potential (spring), chemical potential (fuel).
What is an energy transformation? (example)
When energy changes from one form to another. Example: In a toaster: electrical → heat
What does the Law of Conservation of Energy state?
Energy cannot be created or destroyed, only transformed from one form to another. The total energy stays the same.
What is the difference between useful and wasted energy?
Useful energy: the energy that does what we want (e.g. light from a bulb).
Wasted energy: energy that spreads to the surroundings (usually as heat or sound).
What does a Sankey diagram show?
It shows how input energy is split into useful and wasted outputs.
Arrow width = amount of energy.
Right arrow = useful energy.
Down arrow = wasted energy.
Example: Electrical Energy (100 J)
↓
─────────► Light Energy (10 J)
─────────┐
▼
Heat Energy (90 J)
How do you calculate energy efficiency?
Efficiency=Totalenergyinput / Usefulenergyoutput ×100
Example: Example:
Efficiency= 100/ 10 × 100 = 10%
What are the three main ways heat energy is transferred?
Conduction – heat moves through direct contact (e.g. touching a hot pan).
Convection – heat moves through fluids (e.g. boiling water).
Radiation – heat travels through space by electromagnetic waves (e.g. sunlight).
Describe an example showing the conservation of energy.
A swinging pendulum:
At the top: maximum potential energy.
In motion: kinetic energy.
Eventually, it slows down because energy is transferred to heat and sound, but total energy is still conserved.
What can we learn from a Sankey diagram?
Observation: Most arrows point downward = lots of wasted energy (low efficiency).
Conclusion: Device is inefficient and could be improved by reducing heat loss.
Why is efficiency important?
Because inefficient systems waste energy, cost more money, and increase pollution and greenhouse gas emissions.
Describe the energy changes in a torch.
Chemical (battery) → Electrical → Light (useful) + Heat (wasted).
How does energy from the Sun reach Earth?
Through radiation — energy travels through the vacuum of space as electromagnetic waves.
What happens to unstable systems over time?
They move toward a more stable state by transferring energy to the surroundings, usually as heat.
Sankey diagram comparing an incandescent bulb (10% efficient) and an LED bulb (90% efficient).
Questions:
Which bulb wastes more energy as heat?
Which is more efficient?
What conclusion can we draw about energy-efficient lighting?
Answer/Observation:
Incandescent: 90% wasted as heat → very inefficient.
LED: 90% useful → energy-saving and more sustainable.
