Magnetic Fields Flashcards
Where do arrows in magnetic fields point?
North to South
What is the right-hand rule for solenoids?
Fingers curl in direction of the current, thumb points towards north pole of that solenoid.
What is the right-hand rule for a current-carrying wire?
Thumb points in direction of current, fingers will then curl in direction of field.
What is magnetic field strength known as?
Magnetic flux density, symbol B.
What is flux density defined as?
The force per unit length per unit current on a current-carrying conductor at right angles to the direction of the mag field.
What is the unit for flux density?
Tesla, T
What is 1 Tesla equal to?
The flux density that causes a force on 1N on 1m of wire carrying 1A.
What is magnetic flux?
The number of flux lines passing through an area at right angles to the field the flux passes through. Wb = BA. Basically un-densitying flux density.
What is the formula for magnetic flux linkage?
N Flux = BAN
What is the unit of magnetic flux linkage?
Weber-turns, Wb-turn.
What diagram explains flux linkage?
A coil of N turns with flux flowing straight through the middle of it.
What happens if the magnetic field is at an angle theta to the normal of the face of the coil in flux linkage?
Then N flux = BAN cos theta
What is flux linkage through a single coil of wire?
flux = BA cos theta
What do the symbols represent in the flux linkage equation?
B is magnetic flux density, A is area of wire, N is number of turns of the wire.
What is the fore on a current-carrying wire in a mag field?
F = BIL when perpendicular to the field lines.
What is Fleming’s left-hand rule?
Thumb points in direction of force, 1st finger from north to south in mag field, second finger points in direction of current.
What is the force on a moving charge in a mag field?
F = BQv, v is velocity and Q is charge. At right angles to a magnetic field. If not at a perfect right angle is BQv sin theta.
How do you find the radius of the path of a charged particle in a mag field?
Use mv^2 / r = BQv, so r = mv/BQ
What is the movement of a charged particle in a magnetic field?
Force on this is always at right angles to velocity, so acts as a centripetal force and so it will move in a circular path with a constant speed.
How do cyclotrons work?
- Charged particles (protons) fired into middle of cyclotron
- Mag. field forces charged particles to follow a circular path out of first field
- P.D between 2 fields accelerates particle across gap
- Particle is moving faster so has a larger radius through 2nd field.
- P.D reverses so particle then accelerates again.
- Particle does this a lot, gets very fast then leaves cyclotron.
What are the uses of cyclotrons?
Producing high energy beams of particles, useful for radiation threapy.
What are equations relating to cyclotrons?
r = mv/BQ so time for semi-circle is mpi/BQ = r
so speed upon leaving is v = BQR/m
Period of alternating P.D is 2m pi / BQ
Frequency of alternating P.D therefore = BQ / 2 pi m
