Science · Grades 6–10
Energy transfers and useful output · Revision card
Identify where energy enters, is stored and is transferred out.
Understand the idea
Track the system
Identify where energy enters, is stored and is transferred out.
Conservation
Energy is conserved overall, even when useful output is less than input.
Efficiency is a ratio
Use consistent units when comparing useful output with total input.
Worked examples
A device receives 250 J and delivers 75 J as useful output. Find its efficiency as a percentage.
75/250 × 100 = 30%.
30
In a simple model of a falling object, gravitational potential energy can become
Motion increases as gravitational potential energy decreases.
kinetic energy
Explain without looking
- An efficiency greater than 100% in a basic device calculation most likely signals
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