# S-Cool Revision Summary

## S-Cool Revision Summary

As electricity is all about energy, there are a few energy and power equations that you need to be able to derive and use...

#### Work Done (or Energy) and Power Equations

The definition of voltage tells us that

**So, W = VQ**

The definition of current tells us that, Q = It

**So, W = V I t (Learn this!)**

Of course, we already know that:

**So, Power = V I (Learn this!)**

#### Power and Resistance Equations

**From Ohm's law we know that V = IR. If this equation is substituted into the equation P = IV we can get two new equations:**

Power = I^{2}R

or

*Learn these!*

#### The kWhr

Electrical energy is measured in units of the kWhr so that people can be charged for the amount that they use. At the moment, 1 kWhr of energy costs about 7p.

**energy = power x time**

**kWhr = kW x hr**