# Question Video: Calculating the Potential Difference across a Resistance

An indicator light on a DVD player has a resistance of 300 Ω and the current in the light is 55 mA. How many volts are supplied to operate the light?

01:03

### Video Transcript

An indicator light on a DVD player has a resistance of 300 ohms and the current in the light is 55 milliamps. How many volts are supplied to operate the light?

If we imagine this indicator light as part of an electric circuit, we know that the circuit at least contains this light and that this light has a given resistance and a current running through it. But we don’t really know anything else about the circuit. The nice thing is we don’t need to in order to answer this question of how many volts are supplied to operate the light.

Simply knowing the resistance 𝑅 of this indicator light as well as the current 𝐼 running through it, we have enough information to solve for that potential difference or voltage needed to operate the light. Ohm’s law tells us that this potential is equal to the product of the current and resistance.

So the voltage we want to solve for, 𝑉, is equal to the current, which is 55 times 10 to the negative third amps multiplied by the resistance of 300 ohms. This gives us a result of 16.5 volts. That’s how many volts or potential difference are needed to operate the light.