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# AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] watch

1. What did people write for the ammeter questions?

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2. (Original post by Amanzz)
The added mass doesn't effect damping. Of course damping affects the time period, but the mass added has not increased the damping force, as the time period is independent to the mass added, vmax is independent, and this equation here, the 'drag force' which is what the damping force in this instance is, is denoted below. It is true a damping force changes the time period, but changing the mass doesn't change the maximum velocity , assuming the ring has no significant area, which is a fair assumption. Attachment 425463

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Approximately everything you said there is wrong

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3. (Original post by Disney0702)
What other one?
Lol, a lot of confusion (CD)

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4. For the capicitance Discharge question, what did people get for how long capacitor could be used before needing to recharge

I got 1000
5. (Original post by QueNNch)
Yep emf is 0.12V

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Dont you divide by square root of 2 due to avergae, for 2 marks part ii divided by time seems too generous
6. (Original post by Amanzz)
The added mass doesn't effect damping. Of course damping affects the time period, but the mass added has not increased the damping force, as the time period is independent to the mass added, vmax is independent, and this equation here, the 'drag force' which is what the damping force in this instance is, is denoted below. It is true a damping force changes the time period, but changing the mass doesn't change the maximum velocity , assuming the ring has no significant area, which is a fair assumption. Attachment 425463

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Isn't Stokes' law is for spherical objects?
7. (Original post by Lau14)
What was the typo, don't think I noticed!
The first part of the question used a 150Ω resistor, and the second part a 300,000Ω resistor. This lead to a graph that could not be drawn accurately, as it had to start at 1/2000th of the height of the original line! Clearly they missed a 'kilo' off the 150Ω, or added one in on the 300kΩ
8. (Original post by ssargithan)
Dont you divideutby square root of 2 due to avergae, for 2 marks part ii divided by time seems too generous
No idea
9. (Original post by AR_95)
For the capicitance Discharge question, what did people get for how long capacitor could be used before needing to recharge

I got 1000
YES
10. (Original post by NEWT0N)
YES
YES MAN FINALLY A QUESTION I ACTUALLY GOT RIGHT LOOOOOOL

i was stuck on this one for 20 minutes. Was kicking myself because I had done it before in a past paper!!!
11. Anyone get 1.4 for the height of the mass raised by the energy supplied by the capacitor?
12. (Original post by Lau14)
No, there has been a very similar question to this in a previous year (identical but with different numbers) and what they put for 20 is right
Okay so since when did scales read -ve values? you can't get negative mass?
13. (Original post by NEWT0N)
The point charge is negative
Yes! Thats what i wrote too
14. (Original post by salicional)
The first part of the question used a 150Ω resistor, and the second part a 300,000Ω resistor. This lead to a graph that could not be drawn accurately, as it had to start at 1/2000th of the height of the original line! Clearly they missed a 'kilo' off the 150Ω, or added one in on the 300kΩ
I haven't heard anyone else notice this yet, but it would be bad if they had messed up!
15. (Original post by Amanzz)
The added mass doesn't effect damping. Of course damping affects the time period, but the mass added has not increased the damping force, as the time period is independent to the mass added, vmax is independent, and this equation here, the 'drag force' which is what the damping force in this instance is, is denoted below. It is true a damping force changes the time period, but changing the mass doesn't change the maximum velocity , assuming the ring has no significant area, which is a fair assumption. Attachment 425463

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The formula booklet gives equations that assume damping is negligible. Damping doesn't affect the time period it just decreases the velocity as it always acts opposite to velocity, damping will have a greater effect on something which is light as it has a larger impulse. As I said go do the experiment and see for yourself.
16. (Original post by Chazley123)
Okay so since when did scales read -ve values? you can't get negative mass?
If you've got some digital scales, go put something on them, zero them and then take it off. It's not about what mass actually is, it's about how the scales measure it and magnetic fields.
17. (Original post by Disney0702)
Yes! Thats what i wrote too
Nice. I will admit that the first thing I put was (approximately): "the potential increases with distance away from the force"

I don't see why this wouldn't be right as well. But I changed it immediately after doing part 2ci
18. (Original post by NEWT0N)
Isn't Stokes' law is for spherical objects?
That's true, I was illustrating that stokes' law depends on velocity, which doesn't change what a new mass is added provided that there isn't a large change in surface area.

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19. (Original post by Chazley123)
Okay so since when did scales read -ve values? you can't get negative mass?
Your argument is valid but I've also done Q 20 in past papers and it's definitely -322

Change in direction of current, making force apply in opposite direction. (Flemings LHR)
20. (Original post by Chazley123)
Okay so since when did scales read -ve values? you can't get negative mass?

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