8. Magnetism Flashcards
Electric fields are created by static charge. Magnetic fields are created by moving charge (i.e. current). What is the formula for the magnetic force?
Fb = q ⋅ v ⋅ B ⋅ sin0
B is the magnetic field, measured in Tesla’s
0 = the angle between velocity and B
How do you find the direction of a the magnetic force in a magnetic field?
Right hand rule for a positive charge.
- thumb in direction of velocity
- fingers in direction of B
- palm pushes direction of the magnetic force.
For a negative charge, use your LEFT hand, or use your right hand and ‘push’ with the back of your hand.
Why do magnetic forces do NO work?
W = F ⋅ d ⋅ cos0
cos90 = 0
The magnetic force is always perpendicular to a charges velocity (and thus is displacement).
since magnetic forces do no work, they cannot change KE of a charge (KE is constant)
t or f, if velocity and B are perpendicular, a charge will execute uniform circular motion.
true, and Fb will provide the centripetal force.
Fc = mv^2 / r = Fb = q ⋅ v ⋅ B
How do we find the direction of a magnetic field produced by a current in a wire?
Right hand rule for a positive charge.
- thumb points in direction of current (i.e. velocity of charge).
- fingers curl in the direction of B
for a negative charge, use your right hand but just reverse the direction of the current.
How do you create a uniform magnetic field?
A solenoid. Wrappings of circular wire create a uniform B that goes through the center of the circle.
true or false, B varies with I / r where r is the distance from the wire producing B.
true, increased current increases B, increased distance, r, from the wire producing B, decreases B.
Explain the north and south poles of a bar magnet?
All the electrons in a metal bar orbit their atoms with an electron spin. The accumulation of all this moving charge creates a magnetic field. The magnetic field leaves out of the north end and curls back around to enter at the south end.
how does a metal become magnetized?
place the metal in an external magnetic field (i.e. inside of a solenoid). the atoms polarize to align with the external magnetic field. this polarization causes magnetization of the metal.
Where is the earths north pole?
The north magnetic pole of the earth is actually the geographical south pole. Magnetic field lines come out here and curl towards the geographical north (magnetic south).
