Magnetic flux density
A measure of the strength of a magnetic field, denoted B and measured in tesla (T). Magnetic flux Φ = B·A·cos(θ) where A is area and θ is angle between field and normal to surface. One tesla is the field strength that exerts a force of 1 N on a 1 m long wire carrying 1 A perpendicular to the field.
Formula
Φ = BAcosΘ
Real World
MRI scanners (such as those made by Siemens Healthineers) use superconducting coils to generate magnetic flux densities of 1.5–3 T — strong enough that ferromagnetic objects like scissors become dangerous projectiles near the machine.
Exam Focus
Distinguish flux density B (T) from flux Φ (Wb) in your answer — confusing the two is one of the most penalised errors in electromagnetism questions.
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