Magnetic Forces Flashcards
what is the equation for the force on a current carrying wire that is in a magnetic field
F = BIL
what do each of those variables stand for
- F = force (N)
- B = magnetic field strength (flux) (T)
- I = Current in wire (A)
- L = length of wire in field (m)
what would be the equation for the force if the wire was at an angle of theta (0) to the horizontal and the magnetic field lines were vertical
F = BIL cos0
why would you use cos0 in the calculation if the wire was at angle to the horizontal
- you only need the component of the wire that is perpendicular to the magnetic field
- if the wire is tilted to an angle of theta, the wire would be the hypotenuse, so the horizontal plane the adjacent
- knowing the angle, you can do L*cos0 for the component
in the equation F = BIL sin0, what would the angle theta be made between
the wire and the field lines
using F = BIL, what are the three things that could be done in order to increase the power of a motor
- increase the current through the motor
- increase the number of turns of wire in the motor
- increase the magnetic flux / strength within the motor
what is the core of the coil usually made of in order to maximise the magnetic field strength
soft iron
on a subatomic level, why does the motor effect work when a current carrying wire is at right angles to a magnetic field
- the electrons flowing within the wire are at right angles to the field (as they are the current)
- this means they experience a force at right angles to their direction of motion
- as well as at right angles to the field (left hand rule, 3rd dimension concept)
- if the particle is constrained, like in a wire, the force will be ‘transferred’ to the wire itself
- causing the wire to move
why did i use quotation marks around the transferred
- because a force cant really be transferred in the literal sense
- its more of a transfer of (kinetic) energy from the electrons to the wire
what would be the case if the electron wasnt constrained
- the electrons direction of motion would be changing constantly
- causing it to travel in a circular path while in the field
why does the circular motion of the electron make sense from a mechanical perspective (dont go into centripetal motion lol)
- theres a constant resultant force acting on the electron
- using F = ma, that means the electron is accelerating
- implying that its velocity is constantly changing
- however because the magnitude of the resultant force is constant
- it means the magnitude of the electrons velocity is constant
- correctly suggesting its direction is constant changing
the magnetic field lines are pointing vertically upwards and an electron is moving perpendicular from left to right. what is the direction of the motion and why
- using flemings left hand rule, the first finger would be pointing upwards
- the second finger would be pointing in the direction that conventional current would be flowing
- so it would be from right to left
- making the thumb (motion) point away from me
how does this force pointing away from you result in the circular motion of the electron
- because this force is now a centripetal force
- as you are combining the velocity of the electron that is perpendicular to the direction to the thumb motion into one system
therefore what does the tip of your thumb act as
the pivot of rotation for the particle
what is the equation for the strength of the force on a charged particle moving across a magnetic field
F = BQv
what do each of those variables stand for
- F = force (N)
- B = magnetic field strength (T)
- Q = charge of particle (C)
- v = velocity
what would be the equation when the particle is at an angle between the field lines and its direction of motion
F = BQv sin0
what is the simple way to remember this equation
pronounce it as F = Bev
how is this concept of a particle travelling in a circular motion used when creating anitmatter
- a charged antimatter particle can be held by a magnetic field
- continuously orbiting a central point
- this prevents the antimatter from coming into contact with anything that could annihilate it
what is the equation for centripetal force were talking about in this case
F = mv^2 / r
for any scenario where a charged particle follows a constrained circular path, controlled by magnetic fields, what could you say (equation-wise)
- the force acting on the charged particles at right angles is equal to the centripetal force it experiences
- combining F = BQv and F = mv^2 / r
- BQv = mv^2 / r
if you didnt know what the velocity was, but you know the mass, charge and pd the particle was accelerated through, how could you work out v
- E = QV, so we can work out how much energy the particle has
- this energy would solely be kinetic as it is only being accelerated around in circles
- so you can use KE = mv^2 / 2
- giving QV = mv^2 / 2
- and finally v = the root of (2QV / m)
