2016 Official AQA New Spec AS Level Physics Paper 2 - 9th June 2016

Hi can someone explain how to answer those 2 questions thanks.

For Q31 - you would redraw the circuit from p to Q to see the differnet path where the current would go. This would cause the circuit to split at the first junction, where one route will go through 4R then directly to Q, and the other path would go to R. After this point (following the path from R) it will split again to a 3R and 6R route and then meet up again, just befote the final R resistor then going back to Q.

You should have have the 3R and 6R resistor in parallel, and so you add them together using 1/Rt = 1/R1 +1/R2 and you will get 2R. This 2R should be in series to the two R resistors, so you add them together to get 4R. Finally this 4R resistor is in parallel to to the other 4R resistor (wich goes directly to Q) and so you add these together and you should get 2R

I thought that the new spec of science is linear. Meaning you do all three exams in your third year.What are these exams for?Are they simply exams which you do in order to get predicted grades which don't count towards your actual grade or what?

Can somebody explain uncertainties to me? I'm confused

Absolute uncertainty: The smallest interval you can measure. E.g. On a 30cm ruler the absolute is +/-1mm but when you take a reading there will be an uncertainty on both sides of the ruler so you might have to double the 1mm so +/- 2mm.
If you have repeat readings the absolute uncertainty is the range/2

Percentage uncertainty: absolute/reading * 100
Fractional uncertainty: absolute/reading

Always add uncertainties when values are being multiplied or divided:
g*h = uncertainty in g + uncertainty in h
g/h = uncertainty in g + uncertainty in h

When there is a power such as h^2 you multiply the uncertainty by 2

Also if two values are being added or subtracted the absolute uncertainty is the uncertainties added together then divided by the result of the calculation:
a + b
=
(uncertainty in a + uncertainty in b) / (a + b)


Uncertainty in gradients= (difference between best gradient and worst gradient) / best gradient
You use the error bars on a graph to find these. The best gradient is the line that goes straight through the middle of the error bars and the worst is from the bottom of the bottom error bar to the top of the top error bar.

Uncertainty in y intercepts = (difference in best intercept and the worst intercept)/best intercept

Hope that makes sense

On a 30cm ruler, Assuming the ruler increments in mm, the total absolute uncertainty would be +/- 1mm.

Are you sure? I was told that when taking a reading using a ruler since there are 2 ends to the ruler, each with an uncertainty then there are technically 2 uncertainties so 1mm * 2 = +/- 2mm

I thought that the new spec of science is linear. Meaning you do all three exams in your third year.What are these exams for?Are they simply exams which you do in order to get predicted grades which don't count towards your actual grade or what?

Aye, two ends to the ruler. But assuming the ruler increments in mm's (which it may not), then the uncertainty on each end is 0.5mm. Thus the total uncertainty is +/-1mm.

Oh I see.. ish. If the smallest increment on the ruler is 1mm surely then the absolute is +/- 1mm? (forgetting about the other end)

It's given as half the smallest division - i.e. what it increments by. Thus if the ruler increments in 1mm. The uncertainty (ignoring the other end) will be +/- 0.5mm.

It's given as half the smallest division - i.e. what it increments by. Thus if the ruler increments in 1mm. The uncertainty (ignoring the other end) will be +/- 0.5mm.

Hmm I'm not sure about this, on the spec paper it says it's 1mm:

Aye, this is the total absolute uncertainty. Remember 0.5mm uncertainty at each end.

It accepts 2mm or 1mm for the absolute uncertainty so both are right?

Hmm, not too sure about that but if the mark scheme accepts it then you'll get the marks. I personally use the rule of half the smallest division being the uncertainty at either end.

Okay fair enough. I've always been taught its the smallest division which is a bit strange. I don't know why there is disagreement about this

Aye, this is the total absolute uncertainty. Remember 0.5mm uncertainty at each end.