The formula to calculate resistance is voltage, or potential difference, divided by current equals resistance in ohms. Calculate the resistance created by a power supply with instructions from a math and science teacher in this free video on science formulas.

## Video transcription

Hi, I'm Steve Jones and I'm going to tell you something about resistance and the formula to measure it. Well, what is resistance? Let's just quickly, say that, if I have a power supply of some kind, and I attach it to, for example, a heater, let's say this is a heater, then we know, that the heater gets hot. The heater uses energy, and because it uses energy, we say it has resistance. If it has resistance, it uses energy. The power supply also has a little resistance, and therefore that gets hot, and that wastes energy. But, there is a simple law, called ohms law, which enables us to calculate the resistance of a resistor, say a heater, and the value is given in ohms. Now, the first thing is, we have two quantities in the circuit, which we have to measure. We have, what we call the voltage, V, or the potential difference, more correctly, and we have the current, I. I is the current. We can measure both of these quantities with meters, and we know, that the relationship, between, the resistance, the voltage, and the current is given by ohms law, R equals V, divided by I. For example, let's say that the voltage is twelve volts and the current is three amperes, then, we can simply substitute the resistance, R, is equal to V, twelve volts divided by I, three amps, which, as you can see, twelve divided by three is four ohms. And this is the omega, the Greek symbol, alright, so, four ohms. So, this is briefly, the law which tells us how to calculate resistance.