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# PHY5 Jun 05 Thread watch

1. UMS n boundaries changes 4 every paper tho. The curve that they use to map raw mrks to UMS marks changes according to difficulty and performance in paper.
2. (Original post by tktaylor6)

2)
g varies with h, as satalite get higher h goes down so weight goes down
"g.p.e. gained = weight of satellite x height moved through"

The question was: "What is needed for this statement to be correct" or something similar.

At first, i said g needed to be constant, however, this was covered by the 'weight' in the equation, ie. weight=g.m , so g doesnt need to be constant, it is calculated as part of the weight.

After thinking about it for a while, i put that the orbit needed to be circular, rather than eliptical, as an eliptical orbit would have a constantly changing g.p.e
3. (Original post by haz136)
Ye phy4 was really hard but phy5 was alright. As for this 48µC thing, wot confused me was it said hence find the charge stored in the capacitor, which meant you had to use your answer from the first question. I think I found the total charge then divided it by 2 but I haven't got a clue if it's right. Dunno why but I had a total memory blank.
What I did was totally different from all of you. I used W=½CV2 . But I can't remember the anser I got. I substituted the potential difference and the value of the 4 µF as capacitance.
4. (Original post by Goddess)
What I did was totally different from all of you. I used W=½CV2 . But I can't remember the anser I got. I substituted the potential difference and the value of the 4 µF as capacitance.
W=½CV2 is used to find the energy but the question was asking to find the charge Q=CV. But wat i cant remeber was whether it asked to find the total charge in the circuit or across the capacitor.
5. (Original post by Steve8052)
W=½CV2 is used to find the energy but the question was asking to find the charge Q=CV. But wat i cant remeber was whether it asked to find the total charge in the circuit or across the capacitor.
It was to find the charge across the 4 microF capacitor.
6. (Original post by sonja)
It was to find the charge across the 4 microF capacitor.
Oh damn, theres a mark gone.
Oh and in the standing wave question was the displacement -2,-2.5 and -1.6?
7. How did you guys find the force between the two plates which was x (can't remember the distance) awayfrom each other with the potential difference given?
8. that was ok i thought although i got 900V (somin in that region- high 900's i think ) for the PD to give the electron the intial speed ?
9. (Original post by Goddess)
How did you guys find the force between the two plates which was x (can't remember the distance) awayfrom each other with the potential difference given?
E=V/d=5kN/C

F=EQ=5kN/C * 1.60x 10^-19 C
=8x10^-16N
10. (Original post by sumitk87)
that was ok i thought although i got 900V (somin in that region- high 900's i think ) for the PD to give the electron the intial speed ?
i think i got 481 V :/
11. I Gots That Aswell
12. (Original post by lgs98jonee)
E=V/d=5kN/C

F=EQ=5kN/C * 1.60x 10^-19 C
=8x10^-16N
I didn't do this question . I Feel like a looser !!!
13. (Original post by lgs98jonee)
i think i got 481 V :/
some m8s got that
i was doin it right (using ½mv² but i changed it and used e=mc² )
SUCKS I HAD IT ALL DONE BASICALLY AND I CHANGED IT
14. i was quite happy with my paper, after comin home at lookin on i have changed my mind totaly , i think i flopped
time to get depressed
15. yeh i got 481 as well and sumit i fort the same about the paper and then TSR here just made everything in2 a big Q mrk. I dnt fink im gna check this site afta exams ever again.
16. (Original post by Steve8052)
yeh i got 481 as well and sumit i fort the same about the paper and then TSR here just made everything in2 a big Q mrk. I dnt fink im gna check this site afta exams ever again.
lol same esp phy6 (but im gonna be tempted )
17. (Original post by Steve8052)
W=½CV2 is used to find the energy but the question was asking to find the charge Q=CV. But wat i cant remeber was whether it asked to find the total charge in the circuit or across the capacitor.
Total charge in circuit = the charge on that capicitor anyway.
18. (Original post by Hash)
Total charge in circuit = the charge on that capicitor anyway.
really are you sure? it had one capacitor in series and two in parallel. I found out the total capacitance in the circuit was 2µF. So my answer of 48µC is right?
19. (Original post by Steve8052)
really are you sure? it had one capacitor in series and two in parallel. I found out the total capacitance in the circuit was 2µF. So my answer of 48µC is right?

48µC was the correct answer (I'm positive), and yes the total capacitance in the circuit would be 2µC
20. (Original post by Hash)
48µC was the correct answer (I'm positive), and yes the total capacitance in the circuit would be 2µC
Thanx ur a LIFESAVER!!! i was just trying to calculate how many marks i lost in the paper. But however i still dnt understand how that would be the charge across that one capacitor? Is it something to do with the fact that the other two were in parallel?
And btw, what did you get for the displacements of that standing wave question in PHY4?

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