Hello young scientists! Today, we're diving into the world of Sankey diagrams. Think of these as the energy equivalent of a GPS system - they show us where energy starts, where it's going, and how much gets lost on the way.

Sankey diagrams are like treasure maps for energy. They show us the journey that energy takes as it is transformed from one form into another in a device or a process. Here's a quick guide to understand Sankey diagrams

• Arrows: Each energy transfer is represented by an arrow. Imagine these as roads that energy travels on.
• Width of arrows: The wider the road (arrow), the more energy it's carrying. The diagram is drawn to scale, so bigger arrow = more energy.
• Direction of arrows: Energy always moves from left to right. The journey always starts on the left and ends on the right.
• Lost energy: When energy gets lost, it veers off to the top or bottom of the diagram. Think of it as taking a wrong turn and getting lost.
• Power transfers: Sankey diagrams can also represent power transfers. Power is just energy flow per unit time.

Let's look at an electric lamp. The journey starts with the chemical energy from fossil fuels and ends with the light energy from the lamp. On this journey, some energy gets "lost", meaning it's not useful for lighting up the lamp. For example, only 35% of the original energy ends up as useful light, while the remaining 65% is lost as heat to the surroundings. Just like if you were eating a chocolate bar, but 65% of it mysteriously vanished before reaching your mouth - tragic, isn't it?

Likewise, in an electric kettle rated 2.0 kW switched on for 90s, 180 kJ of energy is supplied to the kettle, but 20 kJ of it is lost to the surroundings. If this were a marathon, the kettle would have started with 180 "energy" runners, but only 160 made it to the finish line (heating the water), while 20 got lost (to surroundings).