What is the 10 or 100w they show in your charger or bulb?

When we see w in our bulb, let's say it says 10w (w = watt), then it means the bulb consumes 10watts of electricity, from consumes it means it converts the energy, in the case of bulb the energy is converted into heat and light.

W = J/S, which means the bulb is consuming 10joules per second.

Let's take an example: As you can see in here in the first image in the left, the volatge in the wires is 5V and the amp = 2, so 2a = 2c/s and 5v = 5j/c then how many joules of energy goes through the bulb, well 5 * 2 = 10j so 10joules mover through the bulb in a second.

So in the end we can say that:

==> if you know the volt and current, you can calculate the electric power/electric energy.

Heating effect of Electricity/Joule heating