This video is about the curl or right hand rule. We use the curl right hand
rule when a moving current induces a magnetic field. We use the curl right
hand rule because an electric current moving in a wire actually induces a
magnetic field, and to find the fields direction we use this curl rule. So you
can see that when the current induces a magnetic field, the magnetic field exists
in a circle around that current, so to find the direction of that circular
magnetic field, if we hold up our right hand in that symbol and say that the
thumb points in the direction of the current, then the magnetic field is going
to curl around in the direction that our hand is curling like that. The curl right
hand rule also works in reverse. If we have a current moving in a circle it
induces a magnetic field coming out of the center of the circle that follows
the direction of our thumb like this, and both right-hand rules can also be
flipped in terms of which event is causing which. Current induces a magnetic
field and a magnetic field also induces a current. This is actually how most of
our electricity is generated. So I'm now going to transition to a separate video
where I'm solving some examples of using this rule on a piece of paper. Okay in
this video we're going to use the curl right-hand rule to find the induced
magnetic field from an electric current. So I'm going to have my right hand in
the shape of that curl symbol and we're gonna see what we can do. So starting up
here I can see that I have a current going straight up so that means that I'm
going to place my thumb pointing up and see how my hand curls around either side
of the page. So I can see right away that on the right hand side, like on this side
of the current, my curl is going into the page, and when I hold my thumb up here
the curl is coming out of the page like this. So that means that for the induced
magnetic field here on the right hand side that's going into the page and on
the left hand side it's coming out of the page.
What's actually happening here is that this is forming a kind of circular
magnetic field where it's coming out like this, going back in like that,
circling around coming back like this, but we can't really represent that
accurately on a 2D surface so we just record where it's coming out and where
it's going in. So that's what that would look like for the second problem. I can
see that the current is coming straight out of the page, so if I hold my thumb
coming straight out I can see that my fingers are aiming in a counterclockwise
direction, and if I just follow that along it's always gonna be
counterclockwise, so that means that the induced magnetic field is going to be
going this way in a counterclockwise direction forward. This one down here I
can figure out what's going on inside the field and outside of the field and
this time I'm going to flip the rule and say that I'm going to use the rule where
my curl represents the current and my thumb represents the magnetic field
that's induced by that current. So if I follow my fingers along this way I can
see that inside of the circle specifically like inside of this circle
my thumb is always pointing up, so that means that inside of the circle the
field is pointing up out of the page and if I follow the curl rule like this
around this way, and I'm just following my thumb around in a circle, I can see
that outside of the circle my fingers are always pointing into the page. So
that means that outside of the circle the induced magnetic field is going to
be pointing into the page specifically.
Finally this one's a little weird. You can see that the current is going up
around this coil and going sideways this way as it winds around, so if I curl my
hand like this, because I can see it starts off it seems closer to me and
then farther away, closer and then farther away, so it's gonna curl like
this. So I can see that the magnetic field induced inside of that coil is
going to point in this direction so that's how you would find the induced
magnetic field direction from the direction of the current that's inducing
it.