What is the current through the
bulb of a flashlight that has a resistance of 5.0 ohms if the flashlight is powered
by a battery with an EMF of 4.5 volts?
If we picture this bulb as part of
a circuit, we know it’s connected in series with a power supply of 4.5 volts and
that the bulb’s resistance is 5.0 ohms. Based on this, we want to solve for
the value of the current, we can call it capital 𝐼, that runs through the bulb. Ohm’s law can help us solve for
this current. It tells us that the potential
difference in a circuit is equal to the product of the current and the resistance of
We can rearrange Ohm’s law to solve
for the current which is what we want to solve for in our particular instance. It’s equal to potential divided by
resistance. The voltage of 4.5 volts divided by
the resistance of 5.0 ohms is equal to 0.90 amps. That’s the current that runs
through the bulb of the flashlight.