Electrical Power (Physics)

Lesson notes

Overview

Power dissipated in a resistor grows with the square of the voltage. This topic is rated intermediate and is number 78 of 227 in Physics. Builds on the basics with relationships, methods and trade-offs.

What you are seeing

The panel above shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.

In depth

The power dissipated in a resistor is P = IV, which with Ohm’s law becomes P = V²/R or I²R. For a fixed resistance, doubling the voltage quadruples the power. This is why a lamp becomes much brighter at higher voltage and why power lines use very high voltages: for the same transmitted power, a higher voltage means a lower current and much less I²R heating in the wires.

Reading the relationship

The expression "P = V²/R" is a compact summary of the idea. It uses the symbols P, V, R; name what each one stands for before you start. Notice that it contains a squared term, so doubling that quantity changes the result by a factor of four, and a ratio, so increasing the denominator makes the result smaller. Then use the sliders to see how changing one quantity changes the others.

A guided exploration

1. Set every slider to its middle value and note the shape of the curve. 2. Move one slider at a time and describe whether the curve shifts, stretches or turns. 3. Find the value where the behaviour changes sharply, then connect it to the formula.

Try this

Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.

Common pitfalls

Check units and directions first. Many mistakes come from mixing up a scalar with a vector, or from using a formula outside the conditions where it holds.

How it connects

It builds on “Parallel Circuits”, the topic before it in Physics. Once you are comfortable, continue with “RC Circuits and Time Constants”.

Why it matters

Physics explains how the world moves, heats, shines and interacts, and the same principles power technology around you.

Where you might use it

Revising “Electrical Power” before a class, exam or certification
Designing vehicles, bridges and devices where motion, forces or waves must be predicted
Understanding how sensors, lasers and communication links actually work
Explaining everyday phenomena such as sound, light, heat and orbits

Frequently asked questions

What is Electrical Power?

Power dissipated in a resistor grows with the square of the voltage. It is an intermediate topic in Physics.

How do I use the Electrical Power simulation?

The panel at the top shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. Move the sliders one at a time, then press Space to pause the animation and look closer.

What does the formula mean?

The expression P = V²/R packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.

Who is this topic for?

Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.

What should I learn before this?

Start with “Parallel Circuits”, the previous topic in Physics. Each topic in a subject builds on the ones before it.

How do I track my progress?

Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.