Magnetic flux measures how much of a magnetic field threads through a surface, and this calculator works it out from the three things that decide it: the strength of the field, the area it passes through, and the angle between them. Enter the magnetic field in teslas, the area in square metres, and the angle between the field and the line perpendicular to the surface, and it returns the flux in webers, updating as you type. The idea is best pictured as field lines piercing a loop: more lines through the loop means more flux. That depends on a strong field, a large area, and the field hitting the surface square-on. The angle matters because only the part of the field perpendicular to the surface counts, so the formula multiplies the field and area by the cosine of the angle measured from the surface normal. When the field is straight through the surface the angle is zero, the cosine is one, and the flux is at its maximum; when the field skims along the surface at ninety degrees, the cosine is zero and no flux passes through at all. This quantity sits at the very heart of electromagnetism, because a changing magnetic flux through a coil is what generates a voltage, the principle of Faraday's law that underlies generators, transformers, induction cooktops and the electric guitar pickup. Understanding how field, area and angle combine to set the flux is the first step to understanding all of those. That makes the tool genuinely useful for physics students learning about magnetic fields, flux and electromagnetic induction and checking homework, and for anyone working with coils, magnets and generators. Using teslas and square metres gives the flux in webers. The formula and a worked example are explained clearly below.
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0.1 Wb
magnetic flux
The angle is measured between the field and the normal (perpendicular) to the surface. 0° gives maximum flux.
How it works
The magnetic flux is the field strength B times the area A times the cosine of the angle between the field and the surface normal. With the field perpendicular to the surface the angle is zero and the cosine is one, giving the maximum flux of B times A. When the field is parallel to the surface, the cosine is zero and the flux is zero.
Worked example
For a field of 0.5 teslas through an area of 0.2 square metres at an angle of 0 degrees: the flux is 0.5 times 0.2 times the cosine of 0, which is 0.5 times 0.2 times 1, giving 0.1 webers. At 60 degrees it would halve to 0.05 webers.
