Video: Calculating the Current through a Resistor

What is the current through the bulb of a flashlight that has a resistance of 5.0 Ω if the flashlight is powered by a battery with an EMF of 4.5 V?

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Video Transcript

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 the circuit.

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.

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