A wetsuit allows a thin layer of water to be between your body and the neoprene suit. Your body heat warms this water and helps keep your body warm. A properly fitting wetsuit will be skin tight to prevent water from leaking out of the suit.
Efficiency = (Useful Work done)/(Total Work done).
This is usually expressed as a percentage.
Example:
For every 200KJ of energy released from coal in a power plant, only 60KJ is converted to...