Calculating Efficiency and Energy Transfers in Devices

The video tutorial explains how to calculate the efficiency of devices using Sankey diagrams, which illustrate energy transfers. It provides examples with a car engine, a light bulb, and an electric fan. The efficiency is calculated by dividing the useful energy output by the total energy output and multiplying by 100%. The tutorial demonstrates this process with detailed examples, showing how to identify useful and wasted energy forms and calculate efficiency percentages.

What is the primary purpose of a Sankey diagram?

• To show the cost of energy

• To detail energy transfers in a system

• To measure the temperature of a device

• To calculate the speed of a process

In the car engine example, what type of energy is considered useful?

• Kinetic energy

• Chemical energy

• Sound energy

• Thermal energy

How is the efficiency of a device calculated?

• By dividing useful energy output by total energy output and multiplying by 100%

• By multiplying useful energy output by total energy input

• By dividing total energy input by useful energy output

• By adding useful energy output to total energy output

In the light bulb example, how much energy is transferred as useful light energy?

• 160 joules

• 200 joules

• 40 joules

• 100 joules

What percentage of energy is wasted in the light bulb example?

• 40%

• 20%

• 80%

• 60%

For the electric fan, what is the efficiency percentage given in the example?

• 50%

• 80%

• 60%

• 70%

How much useful energy output is calculated for the electric fan?

• 1250 joules

• 1000 joules

• 750 joules

• 500 joules