Energy Density in Sustainable Systems
The amount of energy stored per unit mass of fuel, determining how much energy can be extracted and transported.
Formula
Energy Density (MJ/kg) = Energy Content (MJ) ÷ Mass (kg)
Real World
Tesla electric vehicles require large, heavy battery packs because lithium-ion batteries store only ~0.9 MJ/kg compared to petrol's ~45 MJ/kg, illustrating why energy density limits EV range.
Exam Focus
Always quote units (MJ/kg) and compare values numerically — vague comparisons like 'higher density' score fewer marks than specific figures.
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