HomeConcept libraryPhysicsElectromagnetismMagnetism

Physics ElectromagnetismIntroStarter track

Concept module

Magnetic Fields

See how current direction, wire spacing, distance, and superposition set the magnetic field around one or two long straight wires, with the stage arrows and scan graphs tied to the same live source pattern.

Interactive lab

Loading the live simulation bench.

Progress

Not startedMastery: NewLocal-first

Start exploring and Open Model Lab will keep this concept's progress on this browser first. Challenge mode has 2 compact tasks ready. No finished quick test, solved challenge, or completion mark is saved yet.

Let the live model runChange one real controlOpen What to notice

Try this setup

Jump to a named bench state or copy the one you are looking at now. Shared links reopen the same controls, graph, overlays, and compare context.

Saved setups

Premium keeps named exact-state study setups in your account while stable concept links stay public below.

Checking saved setup access.

This concept can keep using stable links while the saved-setups capability resolves for this browser.

Copy current setup

Stable concept and section links stay public below while exact-state setup sharing stays behind premium.

Stable links

Starter track

Step 1 of 30 / 3 complete

Magnetism

Next after this: Faraday's Law and Lenz's Law.

1. Magnetic Fields2. Faraday's Law and Lenz's Law3. Magnetic Force on Moving Charges and Currents

This concept is the track start.

See next concept

Why it behaves this way

Explanation

A magnetic field around a long straight wire circles the wire instead of pointing along it. Current direction sets the circulation sense through the right-hand rule, current size sets how strong that local swirl is, and distance still matters because the field weakens as you move farther from the wire.

This module keeps one bounded two-wire stage, one movable probe, and one linked scan line. The same current directions, current sizes, wire spacing, and probe position drive the field loops, probe vectors, worked examples, prediction prompts, quick test, and compare mode so magnetic-field patterns stay tied to their source instead of turning into a detached rule sheet.

Key ideas

01Positive current in this model means out of the page and produces a counterclockwise magnetic-field circulation. Negative current means into the page and produces a clockwise circulation.

02At one fixed distance from a wire, stronger current gives a stronger magnetic field. At one fixed current, moving farther away weakens the field.

03The net magnetic field at the probe is the vector sum of both wire contributions evaluated at that same location.

Frozen walkthrough

Step through the frozen example

Frozen walkthrough

Solve the current probe state directly from the live controls. The same wire currents, spacing, and probe point now on screen determine the stage arrows, scan graphs, and explanations below.

Premium unlocks saved study tools, exact-state sharing, and the richer review surfaces that support this guided flow.

View plans

Frozen valuesUsing frozen parameters

For the current wire pair and probe point, what net magnetic field vector acts at the probe?

I_{A}

Wire A current

2 A

I_{B}

Wire B current

-2 A

s

Wire separation

2.4 m

x_{p}

Probe x-position

0 m

y_{p}

Probe y-position

1 m

1. Place the two wires on the shared axis

With symmetric placement,

x_{A} = - s /2 = - 1.2 m

and

x_{B} = + s /2 = 1.2 m

2. Build the wire-to-probe position vectors

r_{A} = (1.2, 1)

with

∣ r_{A} ∣ = 1.56

, and

r_{B} = (- 1.2, 1)

with

∣ r_{B} ∣ = 1.56

3. Evaluate each tangential magnetic-field contribution

B_{A} = I_{A} (- Δ y_{A}, Δ x_{A}) / r_{A}^{2} = (- 0.82, 0.98)

and

B_{B} = I_{B} (- Δ y_{B}, Δ x_{B}) / r_{B}^{2} = (0.82, 0.98)

4. Add the vectors at the same probe point

B_{net} = B_{A} + B_{B} = (0, 1.97)

, so

∣ B ∣ = 1.97

Net magnetic field

B_{net} = (0, 1.97), ∣ B ∣ = 1.97

The two wire contributions are closely balanced here, so the final direction has to be read from careful vector addition.

Right-hand-rule checkpoint

Keep both currents equal and out of the page, then place the probe exactly halfway between the wires on the same horizontal axis. What must happen to the two magnetic-field contributions there, and why can the net field vanish even though each wire still makes a nonzero field on its own?

Make a prediction before you reveal the next step.

Predict which tangential directions oppose before you move the probe onto the midpoint.

Check your reasoning against the live bench.

The two contributions are equal in size and opposite in direction at that midpoint, so they cancel and the net field is zero there.

The midpoint sits the same distance from both wires, so equal currents create equal-magnitude fields there. Because the probe lies on the shared axis between the wires, the two tangential directions point opposite ways, and the vector sum vanishes.

Common misconception

If current goes to the right through a wire, the magnetic field near that wire also points to the right.

For a long straight wire, the magnetic field wraps around the wire in circles. It is tangent to those circles, not aligned with the wire itself.

Current direction matters because it chooses clockwise or counterclockwise circulation through the right-hand rule. The probe direction still depends on where the probe sits around the wire.

Quick test

Variable effect

Question 1 of 4

Answer from field logic, not from isolated mnemonics. Each question asks what the stage and graphs must mean about circulation sense, superposition, or field strength around current-carrying wires.

A probe sits to the right of one isolated wire. If the current changes from +2 A to -2 A at the same location, what must happen to the magnetic field at the probe?

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

Accessibility

The simulation shows two long straight wires on a horizontal axis, a movable probe inside a bounded magnetic-field region, and optional overlays for circular guide loops around each wire, a field-sample grid, source-contribution arrows, the net magnetic-field arrow at the probe, and the horizontal scan line used by the graphs.

A dot marker means current out of the page and a cross marker means current into the page. Dragging the probe changes the sampled field location directly on the stage, while dragging either wire marker changes the shared wire separation symmetrically. Sliders provide the same controls for current size and sign, separation, and probe position.

Very near a wire marker, the field display uses a minimum sampling radius so the drawn arrows stay finite and readable. This keeps the visualization bounded while still preserving the correct trend that magnetic field strength grows rapidly near a wire.

Graph summary

The horizontal field-scan graph plots Wire A's horizontal contribution, Wire B's horizontal contribution, and the net horizontal magnetic field along the current scan line. Hovering the graph previews the same x-location on the stage.

The direction-and-strength graph plots the net vertical component and the total magnetic-field strength along that same scan line. Both graphs remain field-only readouts generated by the wire currents and the current probe location.

Keep the source-field story moving

Keep this idea moving

Open the next concept, route, or track only when you want the current model to widen into a larger branch.

Change flux into emfElectromagnetism