Sankey Diagram question?

[Herman]

The idea of Sankey diagrams is that all the energy in one form (in this example, all the energy is coal) is changed into one form or another (i.e. heat and light).

You are meant to use the squares to work out the figures. If you look at the left of the diagram, there are 20 little squares from the top to the bottom of the diagram. 100 kJ / 20 = 5 kJ, so each square represents 5kJ of energy.

Now, count the square width of each arrow pointing downwards. Then, since each square is equal to 5kJ, times the number by 5.

So, i is 13 squares wide. 13 x 5 = 65, so 65kJ is wasted as heat in power stations

ii is 1 square wide, so 1 x 5 = 5kJ, so 5kJ is wasted as heat in power lines.

iii is 6 squares wide, so 6 x 5 = 30kJ is transferred by light bulbs.

Then, if we add these values up, 65 + 5 + 30 = 100kJ, which is the original amount of energy put in. This shows that our calculations are correct as no energy here has been created are destroyed, only transferred.