Efficiency Flashcards
What is the principle of energy conservation?
Energy is never created or destroyed; it just changes into a different form.
How is efficiency calculated?
efficiency = (useful energy output / total energy input) X 100%
In the efficiency formula, what do you need to identify?
The useful energy output and the total energy input.
What is the efficiency of a house losing 125W of heat with heaters producing 800W of heat?
0.84
What is the efficiency of a car that transfers 3,500J to kinetic energy out of 12,500J total energy input?
0.28
How much energy is wasted by a power station producing 400,000 Joules from 1,000,000 Joules input?
600,000 Joules
What is the efficiency of the power station producing 400,000 Joules from 1,000,000 Joules?
0.4
Is the power station described as extremely efficient? Explain.
Less than half of the energy being put in is being used efficiently.
What does a Sankey diagram illustrate?
How well a machine uses energy, indicating efficiency or waste.
What is the efficiency of a light bulb that radiates 20J of light for every 100J of electrical energy supplied?
0.2
How much energy is wasted by a light bulb for every 100J of electrical energy supplied?
80J
An energy-saving light bulb radiates 20J of light and wastes 5J. How much energy is supplied?
15 Joules
What is the efficiency of an energy-saving light bulb that radiates 20J and wastes 5J?
0.6
In a Sankey diagram for a car, what is the useful energy and wasted energy if 75J is useful?
Useful energy: 75J; Wasted energy: 25J
In a Sankey diagram for a light bulb, what are the useful and wasted energies if 36J is useful?
Useful energy: 36J; Wasted energy: 4J
Calculate the efficiency of a device with 75J useful energy and 100J total energy.
0.75
Calculate the efficiency of a device with 36J useful energy and 40J total energy.
0.9
