Electron deflection in a uniform field
https://imgur.com/gallery/Bei5eZZ
please explain part d), the solution i've been given doesn't make sense to me.
please explain part d), the solution i've been given doesn't make sense to me.
Original post by beezo
https://imgur.com/gallery/Bei5eZZ
please explain part d), the solution i've been given doesn't make sense to me.
please explain part d), the solution i've been given doesn't make sense to me.
That question is so brief - is it referring to a diagram from earlier in the book it is taken from? I assume that the plates are arranged so that they are parallel to the direction that the electron is fired into them, after the electron has been accelerated from rest. If that's right, then you need to treat it like a projectile motion problem, with zero horizontal acceleration. The vertical acceleration will be that due to the field between the plates, rather than that due to gravity, but the idea is the same. The electron will either make it between the plates or be attracted to the positive plate to the extent that it collides with it.
But as I say, it's hard to be sure just from that info.
Original post by Pangol
That question is so brief - is it referring to a diagram from earlier in the book it is taken from? I assume that the plates are arranged so that they are parallel to the direction that the electron is fired into them, after the electron has been accelerated from rest. If that's right, then you need to treat it like a projectile motion problem, with zero horizontal acceleration. The vertical acceleration will be that due to the field between the plates, rather than that due to gravity, but the idea is the same. The electron will either make it between the plates or be attracted to the positive plate to the extent that it collides with it.
But as I say, it's hard to be sure just from that info.
But as I say, it's hard to be sure just from that info.
I was thinking the same. I assume it may have been ripped from a book but that's all the info I have. The answer implies that it's velocity from the cathode to anode is constant, but wouldn't the PD across the cathode and anode accelerate it?
Original post by beezo
I was thinking the same. I assume it may have been ripped from a book but that's all the info I have. The answer implies that it's velocity from the cathode to anode is constant, but wouldn't the PD across the cathode and anode accelerate it?
I would assume that it is accelerated from rest by the 3000 V p.d. and then moves at a constant velocity until it encounters the parallel plates. Another thing you have to assume is that it enters the plates exactly half way between them. These are the usual assumptions, but the lack of detail is frustrating.
I would also have thought that for two marks, it is too much to consider whether the electron hits the plates or makes it through. On the assumption that it makes it through, I make the time 2.46 x 10-9 s. But the information about the vertical electric field doesn't get used in this case, and although taking it into account is not difficult, it feels like more than two marks of effort.
Original post by Pangol
I would assume that it is accelerated from rest by the 3000 V p.d. and then moves at a constant velocity until it encounters the parallel plates. Another thing you have to assume is that it enters the plates exactly half way between them. These are the usual assumptions, but the lack of detail is frustrating.
Why do you have to assume it enter the plates exactly half way between them?
Original post by beezo
Why do you have to assume it enter the plates exactly half way between them?
You only have to do this if you're going to worry about whether the electron makes it through or not. If you're doing a suvat in the direction perpendicular to the plates, you know the initial velocity in this direction (nothing), you can work out the acceleration from the force on the electron provided by the electric field between the plates, but to work out how long it will take for the electron to collide with one of the plates, you'll need to know how far it will have to travel in this direction before that happens. It will be 2.50 cm if it the electron enters this region half way between the plates. But as I was saying before, this is a lot of work for two marks. I think that this question has been taken from a longer one, and hasn't been adapted very carefully.
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