What is the source of a magnetic field?
- Moving electric charges.
What is the SI unit for the magnetic field? What is another common unit?
- Tesla, N/(A*m) & Gauss, 10-4 Tesla
How do you draw a magnetic field diagram?
- Arrow points out of the north end, and into the south. The arrow goes in the direction a compass would point.
What do equally spaced magnetic field lines represent?
- Uniform field. Means that when you move through it, the magnetic force doesn't change.
The Magnetic Force on a Moving ChargeEdit
What is the equation for magnitude of magnetic force on a moving charge? (No equation sheet!)
- F = |q|vB(sinθ). Where F is the magnetic force, |q| is the magnitude of the charge, v is the velocity of the particle, and B(sinθ) is the field that is PERPENDICULAR to the velocity.
How do you determine the direction of the force?
- Force is orthogonal to velocity and B. Curl fingers from v to B, and thumb is pointing towards force, for a POSITIVE charge. Negative charges go the opposite way.
What is the difference between an electric and magnetic field?
- A magnetic field acts only on a charge that is moving, whereas an electric field always acts. The direction of the magnetic field is always perpendicular, while the electric field is parallel. A magnetic field does no work, as it is always perpendicular.
What is the equation for the radius of a charge moving in a magnetic field?
- Fcp = macp = m(v2)/r = qvB, solve. r = mv / qB
What is the period of that orbit?
- v = 2πr/T, substitute into r = mv / qB and solve for T, T = 2πm/(|q|B)
The Magnetic Force on a Current-Carrying WireEdit
What is the equation for the force that a current-carrying wire feels in magnetic field?
- F = qvB(sinθ), q = I*t, v = L/t, F = ILB(sinθ)
How do you determine torque on a loop of wire?
- τ = rF(sinθ). Find r, find F. Only the perpendicular wires feel force, and they feel IlB. Radius is easily found. Plug it in.
Magnetic Fields Created by Current-Carrying WiresEdit
What is the equation for the magnitude of a magnetic field of a long, straight wire?
How do you determine the direction of a magnetic field around a long, straight wire?
- RHR. Point thumb in the direction of current, and the fingers curl around in the direction of the magnetic field.
What is the equation for the magnitude of magnetic force of two wires?
- F = ILB, first wire. Find B of second wire, and plug in. F = (µ0/2π)*[I1*I2/r] Newton's 3rd Law says they're equal.
What is the direction of the magnetic force between two wires?
- Do RHR and figure out the directions of force. If current is same direction, attractive. Opposite direction, repulsive.
What is the formula for the magnetic field at the center of a current loop? A solenoid?
- B = Nµ0I/2R
- B = µ0(N/L)I = µ0nI