Magnetic Field Mapping Apparatus

Quick Answer: The Magnetic Field Mapping Apparatus is a demonstration unit for tracing the magnetic field produced by an electric current. The listing image shows an arched metal conductor rising through the top panel of a wooden box, with supply terminals on the front, so iron filings or plotting compasses on the panel reveal the field lines around the wire.

Seeing the Field Around a Current Loop

Any wire carrying a current is surrounded by a magnetic field whose lines form closed circles around it. On this magnetic field mapping apparatus the arched conductor passes down through the flat top panel at two points, so anyone looking at the panel sees two sets of circles, one around each crossing. Between the two crossings the fields from both sides point the same way and add together, giving a stronger, straighter field through the middle of the loop.

That pattern resembles the field of a short bar magnet lying across the loop, and it is the step that links a single current loop to a solenoid and then to an electromagnet. Reversing the supply reverses the field direction, which plotting compasses show at once, while iron filings, having no preferred end, form the same shape either way.

The front panel in the listing image carries several terminals. Which terminal pairs connect to which conductor, and the current the conductor is rated to carry, should be checked with LabEquip before use, since mapping with iron filings usually needs a fairly large current from a low-voltage supply.

Care & Handling

• Switch the supply off between observations; a heavy current warms the conductor and drains cells quickly.
• Collect iron filings with a magnet wrapped in paper or a plastic bag, and keep them out of the terminals.
• Tap the panel lightly to help filings settle rather than shaking the whole unit.
• Keep plotting compasses away from strong magnets in storage so their needles do not lose or reverse their magnetism.

Specifications

Applications

• Drawing field lines around a current loop and comparing them with a bar magnet
• Using the right-hand grip rule to predict and then check field direction
• Showing how field strength falls with distance from the wire
• Introducing the solenoid, electromagnets and electric motors

Why Choose LabEquip

Physics teachers use this apparatus when moving from permanent magnets to electromagnetism, because the loop shape bridges a straight wire and a coil. LabEquip supplies it through the STEM kits range and it pairs well with the Oersted Law Teaching Apparatus, which covers the first observation that a current deflects a compass. Ask about supply options on the contact page.

Frequently Asked Questions

Why do the iron filings form circles around the wire?

Iron filings are magnetised by the field, so each one acts as a miniature compass needle and swings into line with the local field direction. The magnetic field of a current forms closed loops centred on the wire, so the filings settle into rings that are closest together near the wire, where the field is strongest.

How can the direction of the field be found?

Place plotting compasses on the panel; each needle’s north pole points along the field. The right-hand grip rule predicts the same result: point the right thumb along the conventional current, and the curled fingers show the direction of the field lines.

What does the field look like in the middle of the loop?

Inside the loop the circular fields from the two sides of the conductor point the same way, so they combine into lines that run nearly straight through the centre. Outside the loop the lines curve round, giving a pattern similar to a short bar magnet.

What happens when the current is increased?

The field becomes stronger at every point, so filings form a clearer pattern further from the wire and compass needles swing more firmly. Reversing the current reverses the field, and the compasses turn to point the opposite way.

Can the apparatus be used with alternating current?

A compass needle cannot follow a field that reverses many times per second, so direction mapping needs direct current. Filings may still outline the pattern, but a steady low-voltage DC supply is the normal choice for this experiment.

How is this different from a magnetic lines of force tube?

A lines of force tube shows the field of a permanent magnet in three dimensions, using particles sealed in liquid. This apparatus shows the field produced by an electric current, which appears only while the supply is on and changes direction when the current is reversed.

Last Updated: September 2026