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# How to tackle Unit 4 AQA multiple choice questions.

1. Hello all, I have been attempting to answer jan 2010 to june 2014 multiple choice questions, but each time I attempt them I get different results.

I was wondering how you manage to answer or tackle these types of things?
2. (Original post by AQATrolledMe)
Hello all, I have been attempting to answer jan 2010 to june 2014 multiple choice questions, but each time I attempt them I get different results.

I was wondering how you manage to answer or tackle these types of things?
Got any examples of the type of thing you have trouble with?
3. (Original post by Joinedup)
Got any examples of the type of thing you have trouble with?
http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF

Can you have a look at Q 14 please? thanks
4. (Original post by AQATrolledMe)
http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF

Can you have a look at Q 14 please? thanks
first thoughts; D is just copied in from the formula sheet, I'd expect to see √ in the right answer given the layout of the point charges (though maybe best not to jump the gun too soon)

since we're just adding up the contributions of each point charge the +ve and -ve diagonal pair can be seen to cancel leaving us to worry about 2 +ve charges which are both at √2a distance (pythagoras)

formula sheet says Q/(4πε0r)

for 2 charges this is
2Q/(4πε0r)
=Q/(2πε0r)

at distance √2a this is
Q/(2πε0√2a)

---
should also work if you don't notice you can cancel the +ve -ve pair because +3-1=2 anyway.

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