Worksheet: Sankey Diagrams

In this worksheet, we will practice correctly drawing and interpreting Sankey diagrams for processes that involve the transfer of energy.

Q1:

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?

Q2:

The image shows a Sankey diagram for a fluorescent light. What is the input power of the fluorescent light?

Q3:

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?

  • A70%
  • B10%
  • C20%
  • D30%
  • E50%

Q4:

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

What is the efficiency of the kettle?

  • A90%
  • B50%
  • C100%
  • D10%
  • E0%

Q5:

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, c, and e
  • Ba, b, and e
  • Cd, b, and c
  • Da, d, and e
  • Ee, b, and c

Q6:

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 kettle
  • BThe light bulb

What is the efficiency of the kettle?

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

What is the efficiency of the light bulb?

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

Q7:

The image shows Sankey diagrams for four different processes.

Which process is the most efficient?

  • A(b)
  • B(a)
  • C(c)
  • D(d)

Which process is the least efficient?

  • A(d)
  • B(c)
  • C(b)
  • D(a)

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