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In this lesson, we will learn how to correctly draw and interpret Sankey diagrams for processes that involve the transfer of energy.

Q1:

Diagram (a) is a Sankey diagram of a 1.8 kW kettle. Diagram (b) is a Sankey diagram of an 80 W light bulb.

Which device is more efficient?

What is the efficiency of the kettle?

What is the efficiency of the light bulb?

Q2:

The image shows a Sankey diagram for a light bulb that is supplied with 100 J of energy, where 80 J of energy is wasted as heat. What is the useful energy output of the bulb?

Q3:

The image shows a Sankey diagram for a 1.7 kW kettle turned on for 3 minutes.

Is the majority of the energy supplied to the kettle wasted or transferred usefully?

Q4:

The image shows a Sankey diagram for a light bulb that has been drawn incorrectly. In which of the following ways has the diagram been drawn incorrectly?

Q5:

The image shows a Sankey diagram for a car motor that is supplied with 2 4 0 0 J of energy, where 480 J of the energy is converted into useful kinetic energy. How much energy is wasted?

Q6:

The image shows a Sankey diagram of a 100 W light bulb.

What does 1 square of the diagram represent?

How much energy is wasted as heat by the light bulb?

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