The current in a circuit is dependent on voltage. To calculate the current in amps, divide the voltage of the battery by its resistance. For example, if you have a 9-volt battery and it has a resistance of 3 ohms then your current will be 2 amps. Figure: Figure from a previous blog post. (Optional – Remove this section for a shorter article) Figure: Figure from a previous blog post. (Optional – Remove this section for a shorter article) In some cases, when the voltage is not constant, you can’t use Ohm’s law to calculate current because of its resistance changes in response to the changing voltage. In these cases as shown in figure __(figure n), we have to find an alternative way of calculating current such as using measuring resistor R and then solving for I or dividing by R at one particular instance where V is known. For example if it takes 12 mA on average through 100 ohms resistor across which there are 200 volts applied then the instantaneous value is 12/100=12mA*200V = 2400 VA so that will be used instead