6.4 + 6.5 F = BQV and electron beams Flashcards
What is the equation for force of a charged moving particle in magnetic field? What does each symbol represent?
F = BQV f = force b = magnetic flux density Q = charge v = velocity
When taking angles into consideration what does f = bqv become?
F = BQVsinx
Since the magnetic field is always perpendicular to direction of travel for a charged particle what condition do we get from this?
Circular motion
Why does circular motion happen in this case?
The velocity of the particle keeps changing (accelerating) as it is attracted to the centre where magnetic field is. So the force will also act towards the centre.
What equation can we use to work out the distance from centre that a charged particle is orbiting.
mv/BQsinx = r
Why does a charged particle follow a circular path.
Since the magnetic field is always at 90 degrees to direction of travel, so that it will be attarcted towards middle, constantly changing acceleration.
Derive F = BQV using I = nAvq
F = BIL I = nAvq
F = B(nAvq)L
F = Bqv x nAL
since nAL = volume x number of charge carriers it is the total number of charge carriers
F/nAL is the same as F/N , so it is the force acting on one particle!
hence F = BQV
Derive F = BQV using F = BIL, I = Q/T and d = st
F = BIL I = Q/T d = st F = b x Q/T x st F = B x Q x s where s is the length
Why do we use d = st in the above example?
It is the distance covered by a charge carrier due to velocity with time. So the length.
Why are charged particles in a magnetic field a subject to circular motion? - centripetal force
Since the force is always perpendicular to direction of travel, so it will be always pulled towards the middle (centripetal force).
What do we do when we get a question about which side of the wire has higher potential with charge carriers being electrons and a wire being in the magnetic field?
We find the direction of conventional current (opposite to electron flow). Then we use the flemings left hand rule to determine to direction of the force acting on the electrons. The plate/side in that direction will therefore acquire negative charge and the one opposite positive charge.
In the above question why is the pd induced?
Since sides of the wire are both charged and seperated, there is an electric field created and thus potential difference across it.
Why is there an emf/ pd between the plates?
Since there is a change in potential energy in terms of the amount of work that would need to be done to move a charged particle in the electric field(between 2 points).
What devices can be used to produce beams of electrons moving at very high speeds?
cathode ray oscilloscopes
x ray tubes
Why is Voltage x Charge work done?
Sinec v = w/q and also the unit of a Volt is JC-1 and mulitplied by C gives us J. joules
