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This video is about magnetic flux and magnetic flux density.

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One way to define magnetic flux is that it is a measurement of the total magnetic field

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that passes through an area.

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This is the formula that you find in the IB physics data booklet to calculate magnetic

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flux and here are the variables.

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The symbol for magnetic flux is the Greek capital letter phi.

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Let's explore this formula a bit further by examining a magnetic field that passes through

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a given area.

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The arrows represent magnetic field lines.

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Let's assume that the strength of the field is B and the rectangular area that you see

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here is A.

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Theta that you see in the formula in addition to B and A is the angle between the direction

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of the magnetic field and the normal to the area.

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To represent this angle, let's take one of the magnetic field lines and draw the normal

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to the area where this field line intersects the area.

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Theta is the angle between these two lines.

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A special case is when the direction of the magnetic field is perpendicular to the area.

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In this case, theta is zero, so cosine theta is one, hence the magnetic flux equals to

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B times A.

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On most questions in IB physics exams, the magnetic field direction will be perpendicular

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to the area.

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Here are a few more key points about magnetic flux.

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The number of field lines is related to the magnetic flux through a given area.

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Logically, the more lines pass through an area, the larger the magnetic flux will be.

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Of course, this is only true if we compare lines that cut a given area at the same angle.

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The unit of magnetic flux is the Weber and magnetic flux is a scalar quantity.

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Magnetic flux density, the second quantity that we discuss in this video, can simply

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be defined as magnetic flux per unit area.

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There are also more complex definitions for magnetic flux density, but for our purposes

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in IB physics, we can just use this simplified definition.

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From the definition, it logically follows that the unit of magnetic flux density is Weber's

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per meter squared.

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Magnetic flux density is a vector quantity, and it is numerically equivalent to the magnetic

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field strength.

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Since the Tesla is the unit of magnetic field strength, one Tesla is equal to one Weber

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per meter squared.

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This completes our discussion of magnetic flux and magnetic flux density.

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In the next video, we'll learn about Faraday's law and magnetic flux linkage.