Recall and use the equation for electrical power P = I V

4.2.4 Resistance – Power in Circuits

Key Equation

In any circuit, the electrical power delivered by a source is given by $$P = I V$$ where $I$ is the current in amperes and $V$ is the voltage in volts.

Analogy: Water Flow 🚰

Think of the circuit as a water pipe. Current $I$ is like the flow rate of water, voltage $V$ is the pressure pushing the water, and power $P$ is the amount of work the water does per second. The higher the flow or the pressure, the more work is done.

Using the Equation

1. Identify the current $I$ and voltage $V$ in the problem.
2. Multiply them: $P = I \times V$.
3. Check units: amperes × volts = watts.

Example Problem

⚡ A 12 V battery supplies a current of 2 A to a light bulb. What is the power of the bulb?

Solution: $P = 2\,\text{A} \times 12\,\text{V} = 24\,\text{W}$.

Practice Table

Quick Check Questions

• What is the power when a 5 V source drives 4 A?
• How does the power change if the current doubles while voltage stays the same?
• Explain why a high‑resistance bulb (low current) can still be bright if the voltage is high.

Summary

Remember: $P = I V$. The product of current and voltage gives the power in watts. Use this simple rule to solve any power‑related question in IGCSE Physics.