Current Balance Practical for H2 Physics: Measuring Magnetic Flux Density with F = BIl

Q: How does a current balance measure magnetic flux density?
A: It measures the magnetic force on a current-carrying wire, converts a balance reading change into force, then uses the gradient of force against current to find the magnetic flux density.

TL;DR
A current balance turns the magnetic force on a wire into a small change in apparent weight. Convert the mass change to force using F = delta m g, plot F against current I, and use gradient = B l when the wire is perpendicular to the field. The key evaluation points are active wire length, field uniformity, heating, balance drift, and whether the wire is exactly at 90 degrees to the field.

Quick practical map

• TL;DR: Convert balance change to force, then graph force against current.
• Principle: Use F = B I l only when the wire is perpendicular to the field.
• Data Table and Graph: Calculate B from gradient / l and evaluate active length errors.

Pair this with H2 Physics practical lab mastery, H2 Physics spreadsheet skills, and