Magnetic Flux and Magnetic Flux Density

 

This is part of the HSC Physics course under the topic Electromagnetic Induction.

HSC Physics Syllabus

Magnetic Flux and Flux Density

This video explores what magnetic flux is and how it changes with reference to the relationship `\phi =B_(||)A=BAcos\theta`.

 

What is Magnetic Flux and Flux Density?

Magnetic flux is a measurement of the total number of magnetic field lines passing through a given area. Flux density is a measurement of the density of magnetic field lines. It is another name for the magnetic field strength `B`. So, Magnetic flux in a given area equals the flux density multiplied by the area.

Magnetic flux (in Webers, Wb) is given by:

  

$$\phi=B_{||}A=BA\cos{\theta}$$

 

where:

• `B` is the magnetic field strength in Teslas (T) or Wb m^–2.

• `A` is the area of the conductor through which magnetic field lines project in metres squared (m²)

• `\theta` is the angle between the magnetic field lines and the normal area of the area

 

 

From this equation, we deduce that:

• when the surface is parallel to the magnetic field lines, its normal is perpendicular to the magnetic field (`\theta=90°`), thus the magnetic flux is zero.

• when the surface is perpendicular to the magnetic field lines, its normal is parallel to the magnetic field (`\theta=0°`), thus the magnetic flux is maximum. 

Changes in Magnetic Flux

 

Any changes to the area, magnetic field strength and angle `\theta` results in a change in magnetic flux passing through the given area of a conductor.

 

 

For example, a change in magnetic flux occurs when the area moved to a location with differing magnetic flux, either higher or lower.

In the diagram above, a rectangular coil is moved out of a uniform magnetic field (directed into the page). As a result, the coil experiences a decrease in flux. 

  

 

Previous section: Interaction Between Two Parallel Current-carrying Conductors

Next section: Faraday's Law of Induction

 

RETURN TO MODULE 6: ELECTROMAGNETISM