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Concept module

Power and Energy in Circuits

Keep one source and one resistive load in view while current, power, and accumulated energy over time stay tied to the same honest circuit.

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Starter track

Step 4 of 60 / 6 complete

Electricity

Earlier steps still set up Power and Energy in Circuits.

1. Electric Fields2. Electric Potential3. Basic Circuits4. Power and Energy in Circuits+2 more steps

Previous step: Basic Circuits.

Start from track beginning

Why it behaves this way

Explanation

Electrical power tells you how quickly a circuit is transferring energy right now. In one bounded resistive circuit, that rate comes straight from the same voltage, current, and resistance you already use in Ohm's law.

This page keeps the model intentionally small: one source drives one resistive load. That is enough to show how current changes with voltage and resistance, why the load brightens or heats more when power rises, and how energy keeps accumulating over time while the power stays fixed for one chosen setup.

Key ideas

01Power is a rate, while energy is the total transferred after that rate acts for some time.
02At fixed resistance, current follows voltage linearly, but power rises faster because P = VI and I also changes with V.
03At fixed source voltage, increasing the load resistance lowers current and power in this ohmic-load model.

Frozen walkthrough

Step through the frozen example

Frozen walkthrough
Use the current source setting, load setting, and inspected time directly. The same circuit state drives the stage, readout card, overlays, and graphs.

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Frozen valuesUsing frozen parameters

For the current source and load, what current flows and how much power is the load taking right now?

Source voltage

12 V

Load resistance

8 ohm

1. Start with Ohm's law for the one-loop load

.

2. Substitute the current source and load values

.

3. Compute the live current

That gives .

4. Use the power relation on the same live circuit

.

5. Compute the load power

So .

Current and power

This is a moderate-power setup, so the load response is clear without pushing the circuit into the strongest settings.

Energy-over-time checkpoint

Two runs use the same 12 V source and the same 8 ohm load. One stays on for 3 s and the other stays on for 9 s. Which run transfers more energy, and what quantity does not change between the runs?

Make a prediction before you reveal the next step.

Predict whether the power changes or whether only the accumulated energy changes before you answer.

Check your reasoning against the live bench.

The 9 s run transfers three times as much energy because the load power stays the same and energy is power multiplied by time.
With voltage and resistance fixed, the current and power stay fixed too. Time does not change the rate itself here; it only gives that same rate more seconds to accumulate energy.

Common misconception

A larger resistance means the component is working harder, so it must always use more power.

For one fixed source voltage and one ohmic load, larger resistance limits the current more strongly.

Because both current and power fall in that case, the higher-resistance load actually transfers energy more slowly even though the resistance number is larger.

Quick test

Reasoning

Question 1 of 5

Answer from the live circuit logic, not from detached rules. Each question asks what the stage, meters, or linked graphs must mean.

Which statement best separates power from energy in this circuit?

Use the live bench to test the result before moving on.

Accessibility

The simulation shows one battery on the left, one resistive load on the top wire, and one return path on the bottom wire. A readout card on the right reports the live source voltage, load resistance, current, power, accumulated energy, and a short qualitative state label for the load response.

Moving charge markers circulate around the loop to keep the current direction visible over time. Optional overlays add current arrows, source and load voltage labels, a power-rate bar tied to the load response, and an energy meter that accumulates as the run continues or as you scrub the time rail.

The model is intentionally bounded to one ohmic source-load loop. There are no capacitors, inductors, or nonlinear devices, so every displayed change stays tied to the same beginner-level relations among voltage, current, resistance, power, and energy over time.

Graph summary

The energy-transfer graph plots delivered energy against time for the current circuit. Hovering or scrubbing lets you inspect the same moment on the stage and the same cumulative-energy value on the graph.

The current-voltage and power-voltage graphs sweep source voltage while the load stays fixed, so they show the different current and power responses clearly. The power-resistance graph sweeps only load resistance at one fixed source voltage to show why larger resistance lowers power in this bounded model.