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Ch 29: Magnetic Fields and ForcesWorksheetSee all chapters

# Force on Moving Charges & Right Hand Rule

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Sections
Magnets and Magnetic Fields
Summary of Magnetism Problems
Force on Moving Charges & Right Hand Rule
Circular Motion of Charges in Magnetic Fields
Mass Spectrometer
Magnetic Force on Current-Carrying Wire
Force and Torque on Current Loops

Concept #1: Force on Moving Charges & Right Hand Rule

Example #1: Force on Charge Moving at an Angle

Transcript

Hey guys. So, in this example, we are looking for the force on a charge, that's moving through a magnetic field in three different scenarios, let's check it out. So, we want the magnitude and direction of the magnetic force, so we want the magnetic force on a 3 Coulomb charge, so q equals plus 3. So, it's positive, so we're going to use the right hand rule for direction, we would use the left hand if it was negative and it's moving with this velocity here, v equals 4 and it has a 5 Tesla magnetic field, that's the strength 5 Tesla and it is that field is directed in the positive x axis, okay? So, that's the field right there, and we want to know what is this force, if the charge is initially moving in these three directions here. So, in all three cases B is going to the right, but the direction of the velocity is different, here the velocity is going up, here the velocity, because it says positive Y axis, here the velocity is going to the left because it's negative x axis and here, it makes 30 degrees with the y axis. Now, the positive y axis over here, this is a little bit ambiguous because you could make 30 degrees with the positive y over here, right? This guy is 30 degrees away from the positive y but this guy is also 30 degrees away. So, we'll talk about that when we get there. So the equation we're going to use is the only equation that makes sense, is the equation for force on a moving charge, right? Which is q, v, B sine of theta, I know q, v and B, weÕrehich is going to plug those, so the challenge here is just making sure we find the right angle, the correct angle. So, q is 3, v is 4, B is 5, those are given, theyÕre up here and the angle we should use is the angle between the two vectors, between v and B, is the angle we should use, v is up, B is to the right, v is directly up, B is directly to the right, so they're exactly perpendicular to each other, they make an angle of 90 degrees, so sine of 90 degrees, sine of 90 by the way is 1, so the answer is just 60 Newtons, okay? And, what about the directions? Well, we're going to use the right-hand rule. So, remember, my fingers represent multiple lines, so itÕs my B field, it's going to point up like this and, it's actually like this, right,? aAnd my velocity should go up. So, it's already up, so this is the direction I should be looking, for, most ofnotice that my palm is out, my palm is away from me and you got to do this yourself, looking at your page, right? If you put your hand in front of you and you see that your palm is away from you, it's going into the plane or into the page, okay?