The meaning of the word “flux” in the dictionary shows “continuous moving or passing by”. When we are talking about the magnetic flux of any given surface area, we mean the flow of magnetic lines of force in the region. These lines of force constitute the actual magnetic field. It measures the intensity of a given magnetic field. In the SI unit (International System of Units), the unit of measurement for magnetic flux is Weber (named after German scientist Wilhelm Eduard Weber). It is often denoted as Wb. The CGS unit of magnetic flux is Maxwell. One Weber = 108 Maxwell. 

Magnetic Flux Explained

Suppose you place a piece of magnet on a surface. A magnetic field will be created in the area surrounding it. That means there will be numerous magnetic lines of force in this zone. These magnetic lines of force originate in the magnet’s north pole and move towards the magnet’s south pole. 

If we place an object within this magnetic field space, it is obvious some magnetic lines of force will pass through that object. Those lines of force which actually pass through the placed object define the magnetic flux of that specific area. In other words, magnetic flux determines the strength of the magnetic field of that particular area. 

Note: The piece of a magnet placed here is in static form and is not moving.

Some Interesting Facts about Magnetic Flux

We can say magnetic flux is equivalent to electric current, but it has its unique properties.

  • Magnetic flux, or the strength of magnetic lines of force around a magnet, is not uniform. 
  • The value of magnetic flux is higher at those points through which the maximum number of lines of force is passing.
  • Magnetic flux is the strongest near the poles of the magnet. 
  • No two magnetic lines of force can intersect with one another. They always run parallel to its neighbourhood lines. 
  • We always find magnetic flux to be forming a closed circular loop. This is because all the lines of force originate at the North Pole of the magnet and culminate at the South pole. 
  • Magnetic flux is not tangible – we cannot see or touch it. Even though it has photon particles like visible light, it is invisible to the human eye because of its extremely low frequency. 
  • The instrument which is used to calculate magnetic flux is called a fluxmeter.

Mathematical Calculation of Magnetic Flux

Flux is represented by the Greek symbol “phi” (φ). When it is magnetic flux, it is written as φB. Similarly, electric flux is written as φE.

Magnetic flux can be defined as the quantity of magnetism in a specified area perpendicular to the magnetic field. It is calculated by multiplying the magnetic field with the specific surface area. 

This is mathematically represented as:

φB= B.S =B.S. Cos θ

Here,

φB (phi underscore B) = Magnetic flux

B = Magnetic field

S = Surface area of the field

θ (theta) = Angle at which lines of force pass through the area.

We can derive from the above formula that:

  1. The value of magnetic flux is lower if the lines of force meet the specified area at 90 degrees. 
  2. The value of magnetic flux is at its highest when the angle between lines of force and the specified area is 9 degrees. 

Now, the specified area for which magnetic flux is being calculated can be of any size. How do we calculate magnetic flux when the size of the specified area is big: 

 

  1. We have to divide the field surface into smaller sections. 
  2. Calculate the magnetic flux of these smaller sections using the above formula.
  3. Then to get the magnetic flux of the total magnetic field, we multiply the values of magnetic flux of the smaller units. 

Magnetic Flux Density

Magnetic flux density is the quantum value of the magnetic flux in one unit area, where the area is perpendicular to the given magnetic field. In other words, it calculates the strength of the magnetic lines of force within one unit area. The unit of measurement of magnetic flux density is Tesla which is equivalent to Weber/m2.

 

Mathematical Formula to Calculate Magnetic Flux Density

Mathematically, the magnetic flux density of a particular point is calculated by dividing the actual value of magnetic flux by the area of the surface. Now, the area can be of any shape. 

B = φB / A

Here,

B = Magnetic field

φB = Magnetic flux

A = Total Area of the plane 

How is Magnetic Flux Different from Magnetic Field?

Even though these two sound similar, there is actually no similarity. Rather, these are two different properties of a magnet. 

When we are talking about magnetic fields, we mean the area surrounding the magnet. When moving charges enter this zone, they experience a force. It can be either a force of attraction or repulsion. 

On the other hand, magnetic flux defines the strength of those magnetic lines produced by the magnet. This strength is directly proportional to (directly dependent on) the number of lines of force that the magnet produces in that area.

Difference Between Electric Flux and Magnetic Flux

  • When a statically charged particle is placed on any surface, an electric field is formed in the area surrounding it. The electric lines of force that pass through a specific area in this zone are known as electric flux.
  • If a charged particle starts moving, a magnetic field is created around it due to the electric current. The magnetic lines of force thus formed in the region are termed magnetic flux. A similar effect can be observed if the moving charged particle is replaced by a bar magnet. 
  • Their SI units are also different. The unit of measurement of electric flux is called Voltmeter. And as we have already mentioned, the SI unit of magnetic flux is Weber.
  • The only similarity between electric flux and magnetic flux is that both are scalar quantities. 

Conclusion

To summarise the topic, here is a quick recall of some important points:

  • Magnetic flux evaluates the strength of a given magnetic field.
  • Its SI unit of measurement is Weber, denoted as Wb.
  • Fluxmeter is the name of the instrument which is used to measure the magnetic flux. 
  • In any given magnetic field, the value of magnetic flux cannot be constant. It changes according to the position and the distance from the magnet. 
  • The magnetic flux density depends on the number of magnetic lines of force passing through it.