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

Is that the one with the water rising in a very thin tube?

I calculated:

The internal radius:
$r = 1.36 \times 10^{-3}m$

The % uncertainty in internal radius r = 2.97%

You?

Is that the one with the water rising in a very thin tube?

I calculated:

The internal radius:
$r = 1.36 \times 10^{-3}m$

The % uncertainty in internal radius r = 2.97%

You?

Hi there,

Yeah I got exactly $r = 1.36 \times 10^{-3}m$ for the first part

My percentage uncertainty was 3.0 but that's just because I rounded to 2 significant figures!

Do you still have the values of R


Posted from TSR Mobile

Yeah 3.0 is the correct answer. I'll lose marks for incorrect sig figs.


Posted from TSR Mobile

No problem! How's your revision going?

I don't think you'll lose marks to be honest! What sort of values did you get for the gradient etc. in the first question?

It was this part!!

Here's my full answers. I disagree with most, but they're what I basically put haha.
• Gradient at V1=V2 = 0.0494 Volts per second
• Ve/G = 37.7 seconds
• R2/R1 = 2.16 (ratio - no unit)
• V2 adds % uncertainty to R2/R1 as you draw a tangent and don't know where it exactly peaks. V1 adds uncertainty because it's a smaller value so it's nominal uncertainty is a greater portion of its value. When divided these % uncertainties are added.
• Current flows from C2 to terminal Y when V2 is max - positive charge flows from positive plate through Y which discharges C2 through R2, producing the dip in the graph
• Graph of V2 for student is exactly 2.5 times the y values of the V1 graph. Same shape, all values multiplied by 2.5. Y intercept = 4.0 V.
• Systematic error in y would produce curve shifted up or down vertically
• Plotted h against 1/r which gave gradient of 2(gamma)/gp (definitely wrong)
• Units of gamma = Nm^-1
• Thinner match stick would increase (steepen) gradient of y against 1/x
• r = 1.36x10^-3m
• % uncertainty in internal radius r = 2.97%


Posted from TSR Mobile

Hmmm okay, but I don't really know what to do apart from past papers (of which there is a limited amount), I've made notes already so now don't know what more to do to revise!

Does anyone here have good ideas? =D

How about you CD223?

My values for the gradient and Ve/G were slightly different but that's to be expected, I got 2.2 for R2/R1 so that's pretty much the same.

What you put for the gradient is correct I think! Although I did it slightly differently, I said plot (h + r/3) against 1/gρr and the gradient will be 2γ so γ = gradient/2

The answer to that is in the unit. You can also figure out what the answer is since the particles are charged. You know that you can only have charged particles (in the tube)when they lose electrons and for that to happen the electrons emitted from the positive plate (cathode) collide with gas molecules or atoms (i think it's a noble gas) ripping of electrons from the particles ( that's one possibility).
And for conduction to occur there must a flow of charged particles, whether negative or positive, but because you can't have negative ions in the tube, the conduction is due to electrons and positive ions


Posted from TSR Mobile

My values for the gradient and Ve/G were slightly different but that's to be expected, I got 2.2 for R2/R1 so that's pretty much the same.

What you put for the gradient is correct I think! Although I did it slightly differently, I said plot (h + r/3) against 1/gρr and the gradient will be 2γ so γ = gradient/2

I got Nm^-3 hmm do u know what the equation was ?

My book Just says what can we deduce from Gas discharge tube and why it glows.... it doesn't even state what happens

I donno but i did it right after the exam aswell and i got the same answer

Yeah you're right. The book only explains why light is emitted, it doesn't say anything about conduction. That's a big problem, especially in the exam


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