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

1. (Original post by king cobra)
The second bit was just less deflection

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No, it was opposite direction as well. The flux through Q moves to the left as it decreases. The initial flux was to the right -- opposite
2. (Original post by k9000)
Yeah b was incorrect that's what i'm saying
Oh right cool haha
3. (Original post by NEWT0N)
No, it was opposite direction as well. The flux through Q moves to the left as it decreases. The initial flux was to the right -- opposite
Why ?

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4. But that's only due to air resistance which is negligible
5. (Original post by DanTheMan358)
Yeah i thought this, half goes to capacitor half goes to resistor?
Some used in resistance of wires so not 50:50
6. Also for the ring and cone question, i put it has no affect on damping? Because damping is caused by resistive forces and weight doesn't affect acceleration downwards?
7. (Original post by Disney0702)
So did you put weight as the answer?
Yes
8. (Original post by chizz1889)
Some used in resistance of wires so not 50:50
But still? B statement was correct?
9. what did y'all put for the six marker?
10. (Original post by king cobra)
Why ?

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As it initially enters coil Q it is moving in some horizontal direction through Q. Then when it decreases, it moves in the opposite direction because some of it essentially "returns" to coil P to account for the smaller current through P. Thus at any rate the second flux is opposite to the first.
11. (Original post by NEWT0N)
As it initially enters coil Q it is moving in some horizontal direction through Q. Then when it decreases, it moves in the opposite direction because some of it essentially "returns" to coil P to account for the smaller current through P. Thus at any rate the second flux is opposite to the first.
Not in the spec so doubt it

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12. And what was the purpose of the steel wires?
13. (Original post by Humbers)
1. Is newtons as rate of change of momentum is force (newtons 2nd law)
21. I put A as it had the longest side perpendicular to the magnetic field. Its a couple and not looking for flux (so largest area is irrelevant) force on couple is F=BIl so biggest couple was A as it had largest length perpendicular to field
22. I think is 1/root 2 as kinetic energy is proportional to the square of velocity
Im sure a couple is the force acting perpendicular to the axis of rotation multiplied by the distance between the two equal and opposite forces. So the couple is equal to BI(vertical length)*(horizontal length) ie proportional to the area. So the coil with the largest area had the greatest couple and that was B.
14. (Original post by Humbers)
indeed

Weight is a force so has unit N

or

Weight = mg = Kg ms-2 which is another unit of force
Just to be pedantic, it's not another unit of force, N is the unit of force. Kgms-2 is the dimensions of force
15. (Original post by NEWT0N)
There were 3? Hm, maybe they would want you to extend the graph to cover the whole length of the x-axis or something. Or they would not want it to intercept the x-axis but only tend asymptotically to it. I don't know
Maybe for the two areas to be roughly equal.
16. how much time before capacitor needed to be recharged?
17. (Original post by chizz1889)
Yes it is. Rate of change of momentum is MLT ^-1 * L^-1 = MLT^-2
Weight is M * LT^-2 which also = MLT^-2
What do those symbols represent?

Momentum, p=mv [kgms^-1]
Rate of change= (delta)mv/t [kgms^-2]
18. The damping question with ring and cone. The damping force is air resistance, which depends on shape of object, how streamlined it is. It does not depend on mass. hence ring has no effect on the damping forces. But the effect of the damping forces will be less since the ringed cone has more inertia. The question is what the mean by damping? The dissipative forces, or the final effect?
19. Your correct but I think it was option C, B was a 1/2 wasn't it?
20. (Original post by TheRAG)
And what was the purpose of the steel wires?
To increase the strength

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