All magnets have South and North poles
Magnetism and static electricity
Magnetic Field lines
Magnetic field lines are loops that point away from the North and toward the South
Iron filings gather on these magnetic field lines, creating patterns visible to the human eye
Like electric field lines, longer arrows indicate larger field strength
What creates magnetic fields?
3-D nature
Magnetic fields are 3D which is often hard to show on paper
In the exam, a dot with a circle (the circle is most often there but it could just be a dot) around it indicates a magnetic field coming out of the page (think of an arrow head coming at you)
An X indicates a magnetic field going into the page (think of the back of an arrow)
Dipoles of the Earth
The magnetic field in a straight wire with current
The magnetic field forms circles in the plane perpendicular to the length of the wire
Picture washers on a wire - those represent circles of the magnetic field
The right-hand rule
Grasp a pencil with your right hand
Your fingers will curl around the pencil in the same direction the magnetic field curls
Your thumb will point in the direction of the current
==B = 𝜇I/(2πr)==
B: magnetic field
𝜇: vacuum permeability (4π x 10^-7)
I: Current
r: distance between enter of wire to where you’re trying to find the field strength
Solenoid
Force on a moving charge
If the velocity of a moving particle is perpendicular to the magnetic field, a magnetic force is exerted on the moving charge
==F = qvBsin(θ)==
F: magnetic force
q: charge of particle
v: velocity
B: magnetic field
θ: angle between velocity and magnetic field vectors
Right hand rule - “flat finger” rule
Fingers point in the direction of the magnetic field
Thumb points in the direction of the velocity for the positive charge
Palm points in the direction of the force
The right hand rule works for positive particles but for negative particles, the same rules apply if you use your left hand
When acceleration is perpendicular to the velocity, as is the case because the magnetic force is perpendicular to the velocity, the acceleration is centripetal
Force on a current-carrying wire from an outside magnetic field
The force between two parallel wires
Mass Spectrometer
Remember that magnetic forces give charges a centripetal acceleration
Fc = Fb
==mv^2/r = qvB==
If part of the velocity is parallel to the field (theta is not 90 degrees), the charge will take a helical path
Mass Spectrometer: a device used to determine the charge to mass of a particle by arcing them in a magnetic field and finding the radius of its path