# what is megnetic Flux ? how it changes? with some examples.

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what is megnetic Flux ? how it changes? with some examples.

In: 0 A magnetic field has some strength and direction.

Let’s imagine you have a magnetic field pointing upward. You set some paper on a table. The magnetic field points up through the paper.

By making the paper bigger or smaller, you can adjust how much ‘field’ goes through it. Likewise, by lifting one side and changing its angle, you can also adjust the amount of ‘field’ going through it.

This ‘amount of field’ is the flux. Since the field has direction, we must consider that as well. Let us call one side of the paper “in” and one side “out”. When the field goes *in* to the “in” side, it adds to the flux. When it goes out of the “in” side, it subtracts from the flux.

If we lay the paper “in” side down, then the whole field goes into the “in” side and the flux is positive. Flip it over and the flux is negative. Hold it sideways and the flux is zero, since the field passes alongside the “in” and “out” sides of the paper but doesn’t ever point through the paper.

[Here is a visualization.](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTNFU3arqAlMc15WMqkMS38mggJ_adB5pKa-w&usqp=CAU) The leftmost image is the “in side down”, the middle image is the “paper held sideways”, and the final image is the paper being held at some angle called ϴ.

Let’s lay the paper flat again, so the flux is positive (“in” side is down). Now we fold the sheet 90 degrees, so half of it remains flat and the other half is vertical. We know from earlier that the vertical segment has zero flux, so the total flux is now halved.

Now, instead of vertical, we fold that side back down. The paper is folded flat in half. The flux is now zero, since anything going into the “in” side of one half must then go out of the “in” side of the other half.

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Examples usually involve a metal loop. This is because in order to change the magnetic flux in a metal loop, some voltage must form within that loop. This basic idea is used for all large electrical generators.

It is also useful for some pretty cool applications, such as my current favorite, the EPFCG. This thing contains a metal ‘container’ and an explosive. By producing a magnetic field inside of the container, it is made to fill with magnetic flux. Detonating an explosive then crushes the container, forcing it to quickly get smaller. This forces one of two things to happen. Either a large voltage forms due to the sudden change in flux (as the container gets smaller very quickly) or electric current is generated and the flux stays the same.

If the flux stays the same in a shrinking container, then it must be getting denser; the magnetic field must be getting stronger. This allows us to produce insanely strong magnetic fields for a short period. Here’s a quick, simple definition I found: “Magnetic flux is the measurement of the total magnetic field which passes through a given area” -khan academy

Here’s an [image](https://cdn.kastatic.org/ka-perseus-images/144a93251811f0dd92a084a73d2222e96dd2241b.svg) to help visualize. The gray planes on the top and bottom are given as the north and south poles of the magnet. The blue plane is the surface you want to measure the magnetic flux for. And the red arrows are the magnetic field lines.

I’ll also list the equation for magnetic flux, Φ = B*A*cosθ.

B – magnetic field strength

A – area of surface you’re measuring

θ – angle between surface and magnetic field line

Take a circular coil of wires and place a magnet near it. There will be a certain direction that the magnetic field takes from the magnet. A certain amount of that magnetic field will pass through the circular area of the coil of wires. This is the magnetic flux.

Now, if you change the magnetic flux, a current is induced in the wires. There are a few ways to change the magnetic flux. If you look back at the equation above, we can see that the magnetic flux, Φ, will change if B (magnetic field strength), A (area), or θ (angle between area and magnetic field) changes.

The magnetic field strength, B will change if you vary the distance between the magnetic and the coil of wires. The area, A can change if you expand or contract the coil. The angle, θ can change by either rotating the magnet or the coil of wires.

This is the core concept of how a generator works. Take a wind turbine for example. There is a loop of wire in the hub that is connected to the blades. As the wind causes the turbine blades to spin, the wire loop also spins. This loop of wire rotates around a magnetic. This rotation changes the angle between the magnetic field and the area of the loop thus changing the magnetic flux and therefore inducing a current.