Wasted Energy

Only a fraction of the electrical energy we supply to a device is transferred into a useful form of energy. E.g., only about 10% of the 100J or so that we supply to a light bulb is transferred into useful light energy. The rest is transferred into heat energy which goes into the room.

This energy spreads out. It dissipates. It becomes more and more dilute, like adding lots of water to orange squash.

Energy is useful because it can do WORK. It can make things happen. When energy spreads out like this is becomes less and less useful. Only very concentrated forms of energy are useful to us.

The water behind this dam has LOTS of gravitational potential energy	This battery will supply a lot of electrical energy when it is needed.	This Mars bar is a very concentrated store of chemical energy.	These nuclear fuel rods contain a huge amount of potential energy.