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