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‫Welcome back.

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‫So so far, we have covered one application of a cross product, we learned how to compute a moment

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‫vector in 3-D using the cross product.

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‫However, there is another application and quite interesting, actually.

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‫It's in the field of electricity and magnetism.

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‫There is a law in physics that states that a force vector equals Q, V, Cross B, and so Q is a charge

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‫of a particle.

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‫It can be plus some kind of number or minus some kind of number.

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‫V is the velocity vector of that particle and B is the magnetic field.

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‫So the charge of the particle times, the velocity vector of that particle cross the magnetic field

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‫through which that particle goes.

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‫A magnetic field is also a vector because it has a magnitude and direction.

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‫And so let's create a situation now where an electron flies into a magnetic field, the white crosses

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‫our magnetic field vectors pointing into the screen.

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‫It's a uniform field.

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‫If you look at it from the side, it looks something like this.

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‫You see, it's a uniform field and it's the same thing like this.

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‫Only now you're looking at it from above, from here.

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‫All right.

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‫And in red, you have an electron that has a negative charge and the forward velocity vector at time

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‫equals zero seconds.

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‫So I have an exercise for you based on this formula here.

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‫Can you tell me how the electron will move in this magnetic field?

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‫What will it trajectory be?

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‫You don't have to use numbers.

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‫Just tell me the shape of its motion.

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‫Try to draw an approximate trajectory for this electron.

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‫And I will see you in the next video.

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‫Thank you very much.

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‫And see you there.