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Lesson: Sankey Diagrams

Sample Question Videos

Worksheet • 6 Questions • 1 Video

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?

  • AThe light bulb
  • BThe kettle

What is the efficiency of the kettle?

  • A 9 0 %
  • B 1 0 0 %
  • C 1 0 %
  • D 5 0 %
  • E 2 0 %

What is the efficiency of the light bulb?

  • A 2 0 %
  • B 7 0 %
  • C 2 5 %
  • D 1 0 %
  • E 7 0 %

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?

  • AThe majority of the energy is wasted.
  • BThe majority of the energy is transferred usefully.

What is the efficiency of the kettle?

  • A90%
  • B0%
  • C10%
  • D50%
  • E100%

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?

  1. The value represented by one square of the diagram is not consistent.
  2. 1 square of a Sankey diagram should always represent 1 watt or 1 joule.
  3. Sankey diagrams can only be used for energy, not power.
  4. The two output arrows both represent 20 W, but they are of different widths.
  5. The total output power is not equal to the total input power.
  • Aa, d, and e
  • Be, b, and c
  • Ca, b, and e
  • Dd, b, and c
  • Ea, c, and e

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?

What is the efficiency of the light bulb?

  • A20%
  • B70%
  • C10%
  • D50%
  • E30%
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