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This was a question i got in the cie exam today. Cant quote the question exactly but i can remember the question (If you can recall it better than me feel free to correct me). A resistor Y has the diameter D and length L. A resistor Z has the diameter 2D and length L. Calculate the ratio of the drift velocity Resistor Y drift velocity/ Resistor Z drift velocity. I calculated it and got 4.
Hello, I've moved this to physics for you.

I'm not entirely sure which exam you have taken, but there are lots of exam discussion threads here: http://www.thestudentroom.co.uk/forumdisplay.php?f=372 so you might be able to find what you're looking for there.
Reply 2
Avatar for olmomiau
olmomiau
4
Original post by Paranoid_Glitch
This was a question i got in the cie exam today. Cant quote the question exactly but i can remember the question (If you can recall it better than me feel free to correct me). A resistor Y has the diameter D and length L. A resistor Z has the diameter 2D and length L. Calculate the ratio of the drift velocity Resistor Y drift velocity/ Resistor Z drift velocity. I calculated it and got 4.


I think that Z had diameter 2d and length 2l and, as speed is proportional to length and inversly proportional to area (or square of diameter), then v(y)/v(z) = 1/[2*(1/2^2)]=1/[2*(1/4)]=1/[1/2]=2
Not 100% sure, though.
EDIT: the answer is actually 4 as length does not affect drift velocity.
Do you remember how many marks this was worth?
(edited 7 years ago)
Reply 3
Avatar for olmomiau
olmomiau
4
For the last ratio, power dissipated in Y/power dissipated in Z , did you get 2?
Original post by olmomiau
For the last ratio, power dissipated in Y/power dissipated in Z , did you get 2?


I think so, i remember it being the same as the resistance ratio.
Original post by Paranoid_Glitch
x


I see. You have posted the electricity question here, haven't you? are the giving answers not helpful for you? I am trying to solve your question, even if it lasts a bit. Hope to find it out for you.
Original post by Kallisto
I see. You have posted the electricity question here, haven't you? are the giving answers not helpful for you? I am trying to solve your question, even if it lasts a bit. Hope to find it out for you.
Sorry about that, but thanks.
Original post by Paranoid_Glitch
Sorry about that, but thanks.


You have written that you got 4 as the ratio. Would you like to write your calculations down, please? hope to get a picture by seeing your steps.
Original post by Kallisto
You have written that you got 4 as the ratio. Would you like to write your calculations down, please? hope to get a picture by seeing your steps.
Okay. Hopefully it is readable.

FIRST PART: Untitled.jpg
(edited 7 years ago)
part 2.jpg77.7KB
Original post by kallisto
you have written that you got 4 as the ratio. Would you like to write your calculations down, please? Hope to get a picture by seeing your steps.
second part

part 2.jpg
Original post by Paranoid_Glitch
second part

part 2.jpg


SO, I hope that I have found a way to calculate the ratio. Hope that you understand my steps, as I am not able to write in latex. Here it is:

I = Q/t = n*A*e*(L/t); t = D/vd
=> I = n*A*e*(L/(D/vd))

Iy : Iz = n*A*e*(L/(D/vd)) : n*A*e*(L/(2D/vd) = L/(D/vd) : L/(2D/vd) = 1 : 1/2 = 2

If it is confusing you too much, I am trying to write my steps in latex.

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