Magnetism
Magnetic flux
- where
- magnetic flux (Wb)
- flux density (T)
- area (m²)
- angle (°)
Explain this equation
Works out the total magnetic flux passing through a flat area, such as a coil face or a core section. It is the starting point for induction and transformer calculations.
B is flux density in tesla: how concentrated the field is. A is the area in square metres. θ is the angle between the field and the normal, a line at right angles to the surface. cos θ picks out the part of the field that actually passes through the area. Φ is the result in webers.
Flux is like counting field lines through a window. A bigger window or a denser field gives more. Tilt the window and fewer lines pass through, which is what cos θ accounts for.
0.5 T through 0.02 m² face-on gives 0.01 Wb. At 60° that halves to 0.005 Wb. At 90° the field skims along the surface and Φ is zero.
Watch out: measure θ from the normal, not from the surface itself. Convert cm² to m² by dividing by 10,000.
Flux describes the magnetic field passing through a surface. Use the angle to the normal, a line perpendicular to the surface.
For a field perpendicular to the surface, θ is zero and cos θ is one. Convert square centimetres into square metres before calculating.
Enter your values to see the result.
Common mistake
Using the angle to the surface instead of the normal.
Limits
Uniform field over a flat surface.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.