# Induction , Permanent Magnet, Coil

#### Chai

Hi, I could need some help here.....
I have a question to this simulation. Faraday's Law 2.05
So, there happens induction , when a magnet is moved through coil. But I dont understand, why, when the magnet moves through and out of the coil, the sign of the voltage is different & when we change the poles on the Magnet, the sign of the voltage is different too. Why exactly do the voltage sign differ everytime ?
I have some thoughts on this, but im not sure (thats why im asking)
So, my first thought is : when the magnet is moved in to the coil - the magnetic lines from the magnet make a electric difference in the coil... But then I dont understand , how can I explain the different voltage sign.
My second thought is: If the coil hat electric flow already it means it has magnetic field wrapped aroud it. And when the magnet is moving into the coil, it strengthens the magnetic field of the coil or it weakens the magnetic field of the coil , and it depends then on the polarity of the magnet whether it stregthens or weakens. (Farradays Law)
So maybe, if the 2nd explanation is right, then based on the Lenz' Law - induction operates in opposite direction to it cause -->
So by weakening the mfield (Cause) voltage is in positive direction, by strenghtening (cause) voltage in negative direction.

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#### studiot

A magnetic field has direction (it is a vector if you know what that is).
It points from North to South, all the way along the lines of the field.
If you turn the magnet round then the field lines are pointing the other way.
So it should not be suprising that the induced electric voltage also reverse direction.

topsquark

#### Chai

A magnetic field has direction (it is a vector if you know what that is).
It points from North to South, all the way along the lines of the field.
If you turn the magnet round then the field lines are pointing the other way.
So it should not be suprising that the induced electric voltage also reverse direction.
Hi,
Thanks, that has brought me further...
Why then ist the voltage reverse by changing the direction of moving? Is it the same as with the changed Magnetic Field Direction?
And, by putting the magnet into the coil its one direction, and by taking it away from the other side the direction changes too.

#### benit13

The formula for the magnetic force on a current carrying conductor is:

$$\displaystyle \vec{F} = I (\vec{l} \times \vec{B})$$

This works for any wire length (l) orientation and magnetic field (B) orientation, but it requires knowledge of vector mathematics and how to compute the cross product.

Because of the cross product, the force is always a right angles to both the wire orientation and the magnetic field. Think of it this way... if you draw an arrow that represents the wire and another arrow that represents the magnetic field direction, you can draw a plane which has both arrows on it (like a piece of paper). The force arrow is therefore an arrow that points out of the plane (perpendicular to the paper).

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topsquark