How do you calculate energy efficiency?

Answer 1

You do this experiment:

• Wear safety specs
• Weigh food (take the mass)
• Heat proof mat under food
• Measure 10cm3 water
• Measure the temperature of the cold water
• Let food catch light
• Put lighted food under test tube (water)
• measure temperature

Find the difference in the start temperature and the end temperature (oC)

Energy = Mass of water X a constant X change in temperature

Answer 2

It is impossible to 'lose' energy. It is simply transformed from one form to another. Maybe you could explain the question better? I had a question where I had to calculate the 'lost energy':

A 90% efficient 2 kW water heater is switched on for a period of 5 hours. The energy lost will be

a) 1kWh

b) 2kWh

c) 5kWh

d) 9kWh

If the heater is only 90% efficient, it will be using 1800 watts efficiently and wasting 200 watts per hour. 200 x 5 hours = 1000 watts.

Answer 3

Energy out divided by energy in give efficiency.
in general this could be seen as

N.eff = (effect as seen in practice or real situation) / (effect as theoretically calculated)

Answer 4

Energy efficiency is typically calculated by dividing the useful output energy by the total input energy and then multiplying by 100 to get a percentage. Useful output energy could refer to things like light produced by a bulb or heat provided by a furnace, while input energy would be the electricity or fuel used to power the device. The higher the percentage, the more efficient the device is at converting input energy into useful output.

Answer 5

Ideally, energy content of any subject is equivalent to the "energy which is required to destruct the subject".