Magnetic Flux
Flux through a surface in a magnetic field.
Formula
Variables
How it works
Magnetic flux measures how much magnetic field passes through a chosen surface. It depends on the field strength, the size of the surface, and how the surface is tilted: only the component of the field perpendicular to the surface contributes, which is why the factor cosb8 appears. If the surface is turned edge-on to the field, the flux is zero; if it faces the field directly, the flux is largest.
When to use it
Use this formula whenever you need the magnetic flux through a loop, coil, or flat surface in a uniform magnetic field. It is especially useful in problems involving electromagnetic induction, where a changing flux produces an induced emf.
Worked example, step by step
A square loop has area A = 0.020 m^2 and sits in a uniform magnetic field of B = 0.50 T. The angle between the magnetic field and the surface's normal is b8 = 30 b0. Use a6_B = BA cosb8. a6_B = (0.50)(0.020)cos(30 b0) a6_B = 0.010 d7 0.866 a6_B = 0.00866 Wb Final answer: a6_B 08.7 d7 10^-3 Wb
Common mistakes to avoid
- Using the angle between the field and the surface instead of the angle between the field and the surface normal
- Forgetting that only the perpendicular component of the magnetic field contributes to flux
- Mixing up units and writing flux in tesla or square metres instead of webers
Did You Know?
Magnetic flux counts field lines through a loop, and only a changing flux generates a voltage.
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