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# AQA Physics Unit 1 PHYA1 20th May 2013 watch

1. (Original post by Xiomara)
For the last one, was it 6-1.5V, so the variable resistor had 4.5 V over it, then you divided that by the current to get the resistance?

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Yeah that's what I did and got 30000 ohms
2. (Original post by Maloneyyy)
What did everyone put to show that the circuit conserved energy?
I put that the overall power of the circuit was 50.2W or something like that and then i took away all of the work done by the resistors and got a negative answer?
Yeah I think I fluffed that one up too, as I also got 50.2W as the overall power and then 58W as the work done by the resistors... I just kind of write a conclusion saying the numbers should be the same and therefore energy is conserved ahaha.
3. (Original post by Tuya)
Probably 2 marks if you carried that negative to the next part, I almost did exactly that, but I found out when I checked for the second time

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Okay thanks, I checked through 3 times, but it didn't seem to click until I left then exam. Damn my primitive brain!
4. (Original post by BenChard)
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they asked for the ion, I did

2x.6x10'-19 / (mass of protons neurons and electrons) is this wrong
As they wanted the ion, and there were 2 more protons than electrons (and neutrons obvs dont have charge)

I did what you did and got 3.2x10^-19
5. Electricity

1) 1.5X4.2=6.3

2) p.d across 2 ohm resistor

12-6.3=5.7V

3) Current across 2 ohm resistor

5.7/2= 2.85

4) Current across R resistor

4.2-2.85=1.35

5) resistance of R resistor

5.7/1.35=4.2

6) total resistance of circuit

Came out to about 2.85 3sf

7) Power in internal resistance=26
Power in 2 ohm=16
Power in R= 7

8) show energy is conserved

Total power of circuit = 2.85X 4.2^2=50W

Power of internal resistance + 2.0+ R = 26+17+7= 50W

Therefore energy is conserved is how i showed my mine

The figures are all rounded but I obviously was doing it to 3sf

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6. (Original post by Alex Newton)
As they wanted the ion, and there were 2 more protons than electrons (and neutrons obvs dont have charge)

I did what you did and got 3.2x10^-19
just finished exam,was super tough,any ideas on grade boundaries?
7. And what did people get for the oscilloscope thing?

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8. So how did it go for everyone?
9. (Original post by posthumus)
I got stuck by far on the first one

after numerous crossing out... I went for 18 x 1.6x10^-19 because when the atom is neutral you don't do 0/mass

And it was only 1 mark, so I just thought it had to be that :/

So confused though still
Did you do 18 x 1.6x10^-19 for the charge of the ion in the specific charge question?
10. (Original post by posthumus)
I got stuck by far on the first one

after numerous crossing out... I went for 18 x 1.6x10^-19 because when the atom is neutral you don't do 0/mass

And it was only 1 mark, so I just thought it had to be that :/

So confused though still
If you think about it like this; If there is an equal amount of protons and electrons the overall charge will be 0 as they cancel each other out. Similarly, if there is a difference of 2, then 18 of the electrons will cancel with 18 of the protons, leaving 2 left. You then multiply the charge of the proton by 2, as that's all the charge there is. Hope that made a tiny bit of sense? Usually wouldn't explain it like that but I went for something a little abstract
11. (Original post by Tuya)
And what did people get for the oscilloscope thing?

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2ms for X base

and Y base 20V... I first did 10V but then realized the curve under the equilibrium so has to be double that to fit it in
12. I thought it was fairly straightforward
13. (Original post by Tuya)
And what did people get for the oscilloscope thing?

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64V peak
128V peak-to-peak
45V for rms voltage
10ms
100Hz

Wasn't sure about the "describe how you would use the oscilloscope" question, though. I just explained how I would set the axis... any ideas?
14. (Original post by usycool1)
I thought it was fairly straightforward
It was all fine but I did the algebra wrong on the last question!! Kicking myself lol! should get 2/3 on it though
15. (Original post by posthumus)
2ms for X base

and Y base 20V... I first did 10V but then realized the curve under the equilibrium so has to be double that to fit it in
Exactly what I got, did you reckon I'll get the 3 marks just by saying that?
16. (Original post by Rrobba)
64V peak
128V peak-to-peak
45V for rms voltage
10ms
100Hz

Wasn't sure about the "describe how you would use the oscilloscope" question, though. I just explained how I would set the axis... any ideas?
Yeh I has a time base of 2ms/division and 16V/division to get 2 complete cycles on the screen
17. (Original post by usycool1)
I thought it was fairly straightforward
How many marks was the rms plotting question ? Didn't even do it !

What'd you do for the first question

& Also what'd you get for the final questions

Thanks !
18. (Original post by posthumus)
2ms for X base

and Y base 20V... I first did 10V but then realized the curve under the equilibrium so has to be double that to fit it in
I got exactly the same as you

EDIT: Actually, I got the same time base but 16V div^-1 for the y-gain

(Original post by g.k.galloway)
It was all fine but I did the algebra wrong on the last question!! Kicking myself lol! should get 2/3 on it though
Ah well, just one mark I threw away a mark on the Oscilloscope question where they asked us to draw the d.c. one...I put a straight line on the peak voltage instead of the rms voltage for some reason Ah well, the rest was OKish
19. (Original post by g.k.galloway)
Yeh I has a time base of 2ms/division and 16V/division to get 2 complete cycles on the screen
Got exactly this.

(Original post by Rrobba)
64V peak
128V peak-to-peak
45V for rms voltage
10ms
100Hz

Wasn't sure about the "describe how you would use the oscilloscope" question, though. I just explained how I would set the axis... any ideas?
Got exactly these too
20. Well that was one piss easy exam! Finished with like 30 minutes to spare. Full marks here I come.

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