Understanding Efficiency: Examples and Equations

The video tutorial explains how devices transfer energy and the concept of efficiency, which is the percentage of input energy that is usefully transferred. It provides three examples: a light bulb, a speaker, and an electric motor, illustrating how to calculate efficiency using different forms of energy. The light bulb transfers only 8% of its energy as light, the speaker converts 48% into sound, and the electric motor has a 5.2% efficiency in lifting a mass. The remaining energy in each case is wasted as thermal energy.

What is the efficiency of a device?

• The useful energy output multiplied by the total energy input

• The total energy input multiplied by the useful energy output

• The total energy input divided by the useful energy output

• The useful energy output divided by the total energy input

In the light bulb example, what percentage of electrical energy is converted into light energy?

• 8%

• 5.2%

• 48%

• 92%

How much of the speaker's electrical energy is converted into sound energy?

• 48%

• 52%

• 92%

• 8%

What is the efficiency of the electric motor in the third example?

• 92%

• 8%

• 48%

• 5.2%

What formula is used to calculate the gravitational potential energy gained in the electric motor example?

• F = MA

• MGH

• P x T

• E = MC^2