AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread]

Could anyone help me on 2cii please. Not too sure how to go about it. http://filestore.aqa.org.uk/subjects/AQA-PHYA5-1-QP-JUN12.PDF


Posted from TSR Mobile

How's everyone going about today then?

How's everyone going about today then?

It's the ratio of the area of the detector compared with the area of where the radiation will go. ie. the surface area of a sphere (4pir^2)

Fancy explaining part Bii to me?

sorry I meant 3bii too, I don't understand how that equals activity lol

No worries!

No. They suffer from chromatic aberration.


Posted from TSR Mobile

In my notes it says refracting telescopes suffer from chromatic and spherical whereas reflecting only suffer from spherical :\

You have more faith in my abilities than I do . Thank you though, and good luck for tomorrow and FP2!

Oh does it? I could be wrong. I've just always been taught the opposite. What notes are they from?

EDIT: I guess you could have "spherical" aberration if the curvature of the lens is not designed properly? Is that what your notes say?


Posted from TSR Mobile

Notes are vague, they only say that it is easier to correct in mirrors.
Googling tells me that only lenses of perfect form don't have problems with spherical aberration.

If I remember correctly, one in 400 of the photons incident on the detector are actually picked up.

So the activity ACTUALLY incident on the detector is 400 x 0.62.

This means that, using the ratio of number of photons incident on the detector over the number produced by the source, divide the activity actually incident on the detector by the ratio you've just worked out:


(0.62 x 400) divided by 4x10^-3 or whatever the ratio was. Hope that helps


Posted from TSR Mobile

Does this help?



There are initially 3 x 10^22 atoms of U.

The half life of U is 4.5 x 10^9 years so there must be 1.5 x 10^22 atoms of U and 1.5 x 10^22 atoms of Pb after one half life. This is where they intersect on the graph.

After another half life, the U curve halves again. Conversely, the Pb curve doubles. They are the mirror of one another.


EDIT: lol, just seen its part two. Ignore me. I'll get on the case.

...

Right, you know that when there are twice as many U atoms as Pb atoms, the ratio is 2:1. This means that the number of U atoms is two thirds the total number.

So the number of U atoms is:

$[br]\dfrac{2}{3} \times 3.0 \times 10^{22}[br][br]= 2.0 \times 10^{22}[br]$


Posted from TSR Mobile

Yeah that makes sense now, thanks

How's everyone going about today then?

Question for turning points.

Special relativity:
Is the length for the observer always shorter than that for the person travelling?

Is the rest mass always smaller than the mass due to its speed


Is the time always shorter for the moving particle

Basically
Is length observer<moving object

Mass : m0<m

Time t<to

I know this is confusing but can someone just simply lay it out for me please


Posted from TSR Mobile

That's right, but i assume for the length you are referring to the length of the moving object.


Posted from TSR Mobile

Yeah that's what I meant! Just wanted to know as a mental check so I know I'm right


Posted from TSR Mobile

Oh cool. Yeah i know, when you make a comparison the results seem to contradict each other as in m>m0 whereas t<t0 because you expect t0<t as in the case with mass. I prefer to think about them to distinguish them so for example i know that time slows down for a uniformly moving object


Posted from TSR Mobile