Improving Efficiency in Real Systems

Efficiency measures how much of the input energy is usefully transferred:

$\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$

No real system is 100% efficient. Improving efficiency means reducing wasted energy.

Mechanical systems

Strategy	How it works
Lubrication	Reduces friction between moving parts
Streamlining	Reduces air resistance (drag)
Lighter materials	Less energy needed to accelerate
Smoother surfaces	Reduces contact friction

Electrical systems

Strategy	How it works
LED instead of filament bulbs	More light per joule, less heat
Lower resistance cables	Less energy dissipated as heat ($P = I^2R$)
Power factor correction	Reduces wasted reactive power

Thermal systems

Strategy	How it works
Insulation (walls, loft, pipes)	Reduces conduction and convection losses
Double glazing	Trapped air reduces conduction
Draught-proofing	Reduces convection losses
Reflective surfaces	Reduces radiation losses

Efficiency vs cost

Some efficiency improvements are expensive to install but save money over time. Loft insulation is cheap with a short payback time. Solar panels are expensive with a longer payback time.

Common errors and how to correct them

• Stating efficiency as greater than 100% (check your calculation; total output cannot exceed total input).
• Confusing power and energy in efficiency calculations (both can be used, but be consistent).

How to apply this in an exam

Identify the useful output and total input. State what the wasted energy is and how the waste could be reduced. Give a specific method, not just “reduce waste”.