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# AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread] watch

1. (Original post by duncant)
gravitation potential is the work done per unit mass to move a small test mass from infinity to that point in a gravitational field.
2. (Original post by rory58824)
I thought like charges repel?
They do. The charges arent the same. One is more positve than the other relative to each other so one is postive and one is negative in effect,.
3. Is it because in this particular instance the lines of action coincide? which is why in the position shown its not a couple, but usually it would be a couple?
4. (Original post by mcride98)
The work done per unit charge to move a small postive test charge from infinity to that point.
5. Yep just checked it is because of the direction of the forces, at this one instance its not a couple, if it was displaced even marginally in any direction it would become a couple....I think :-)
6. (Original post by philo-jitsu)
How are the forces not a couple then? if they are pointing towards one another they are two equal in magnitude forces that oppose one another....isnt that a couple?
A couple is where the forces cancel each other out but there is a resultant moment. In that case the forces cancel each other out but there is no resultant moment
7. (Original post by SirRaza97)
Like this. Sorry its in landscape.

They are both positive.
(Original post by rory58824)
I thought like charges repel?
Check page 22, I kind of explained it there .
8. Hey, can someone help me with January 2010 Question 4b(iv). I've got the wasted energy, but I don't get where the 3.6x10^6 comes from

http://filestore.aqa.org.uk/subjects...W-QP-JAN10.PDF
9. (Original post by Imtheish)
Is anyone having trouble doing past papers in time cause I am. What can I do to improve I know day before the exam. 😅🔫
(Original post by thatguitarist7)
Hey Guys

Any tips on how to manage time in the exam? I.e answer the paper first and get to the multi choice after?
Or is it just try and plough through it all in the time

Cheers

I would advise doing as much as you can in the multpile choice in the recommended time and then move on to section B. The complete section A with the extra time you have left over. Dont spend too much time ona question otherwise time will get pretty short.
10. (Original post by SirRaza97)
Like this. Sorry its in landscape.

Thanks!
11. (Original post by particlestudent)
They are both positive.

Check page 22, I kind of explained it there .
Is that pic he drew wrong then?
12. (Original post by Ayaz789)
Thanks!
I am wrong. Sorry!
13. (Original post by particlestudent)
They are both positive.

Check page 22, I kind of explained it there .
Yes, I was worryingly searching through my textbook for a moment there.

(Original post by SirRaza97)
I am wrong. Sorry!
Don't do that again pls.
14. (Original post by SirRaza97)
I am wrong. Sorry!
Haha its fine, draw it again and show me?
15. Im doing June 2012 section B q4(c), could anyone tell me how many marks i would get for the 6 mark question:
The gravitional field strength of the earth is greater than that of the moon. This is because the earth has a greater mass. As a result of this the point X where the resultant gravitational field is zero is closer to the moon. Therefore when leaver the surface of the earth more energy is required to get a spacecraft to the moon than when leaving the surface of the moon to get to the earth. This is because the gravitational force at the surface of the earth is greater than at the surface of the moon so more force is required to overcome it. Also there is a greater distance to travel to point X so more energy is required.
16. (Original post by Ayaz789)
Is that pic he drew wrong then?
Yes it was, this is for the 4nC and 6nC positive point charges right where you have to draw their field lines right? If so check pg22.
17. (Original post by ReeceFraser)
Im doing June 2012 section B q4(c), could anyone tell me how many marks i would get for the 6 mark question:
The gravitional field strength of the earth is greater than that of the moon. This is because the earth has a greater mass. As a result of this the point X where the resultant gravitational field is zero is closer to the moon. Therefore when leaver the surface of the earth more energy is required to get a spacecraft to the moon than when leaving the surface of the moon to get to the earth. This is because the gravitational force at the surface of the earth is greater than at the surface of the moon so more force is required to overcome it. Also there is a greater distance to travel to point X so more energy is required.
Max 4, I think you need to mention potential for the last 2 marks.
18. (Original post by boyyo)
Does anyone recall using the right hand rule in any of the past papers
Yes - whenever you have to talk about the direction of a charge in the magnetic field you can say "Because of Flemings left hand rule it will in go in X direction (or the opposite if its negatively charged"
19. (Original post by particlestudent)
Take a look at this diagram to give yourself an idea of what they mean. Modify that diagram to suit the magnitude of the charges they used.
So it'll look like this?
20. (Original post by particlestudent)
Max 4, I think you need to mention potential for the last 2 marks.
In what way?

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