Magnetic Forces Flashcards

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1
Q

what is the equation for the force on a current carrying wire that is in a magnetic field

A

F = BIL

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2
Q

what do each of those variables stand for

A
  • F = force (N)
  • B = magnetic field strength (flux) (T)
  • I = Current in wire (A)
  • L = length of wire in field (m)
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3
Q

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

A

F = BIL cos0

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4
Q

why would you use cos0 in the calculation if the wire was at angle to the horizontal

A
  • 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
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5
Q

in the equation F = BIL sin0, what would the angle theta be made between

A

the wire and the field lines

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6
Q

using F = BIL, what are the three things that could be done in order to increase the power of a motor

A
  • increase the current through the motor
  • increase the number of turns of wire in the motor
  • increase the magnetic flux / strength within the motor
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7
Q

what is the core of the coil usually made of in order to maximise the magnetic field strength

A

soft iron

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8
Q

on a subatomic level, why does the motor effect work when a current carrying wire is at right angles to a magnetic field

A
  • 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
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9
Q

why did i use quotation marks around the transferred

A
  • 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
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10
Q

what would be the case if the electron wasnt constrained

A
  • the electrons direction of motion would be changing constantly
  • causing it to travel in a circular path while in the field
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11
Q

why does the circular motion of the electron make sense from a mechanical perspective (dont go into centripetal motion lol)

A
  • 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
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12
Q

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

A
  • 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
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13
Q

how does this force pointing away from you result in the circular motion of the electron

A
  • 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
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14
Q

therefore what does the tip of your thumb act as

A

the pivot of rotation for the particle

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15
Q

what is the equation for the strength of the force on a charged particle moving across a magnetic field

A

F = BQv

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16
Q

what do each of those variables stand for

A
  • F = force (N)
  • B = magnetic field strength (T)
  • Q = charge of particle (C)
  • v = velocity
17
Q

what would be the equation when the particle is at an angle between the field lines and its direction of motion

A

F = BQv sin0

18
Q

what is the simple way to remember this equation

A

pronounce it as F = Bev

19
Q

how is this concept of a particle travelling in a circular motion used when creating anitmatter

A
  • 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
20
Q

what is the equation for centripetal force were talking about in this case

A

F = mv^2 / r

21
Q

for any scenario where a charged particle follows a constrained circular path, controlled by magnetic fields, what could you say (equation-wise)

A
  • 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
22
Q

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

A
  • 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)