(New 2017) AQA A-level Physics 7408 [Exam Discussion]

Original post by thelegend99

Aye lad, same here. People here have really been helpful, especially @Kyou and @Rexar

:biggrin:

let's do this!

Aww thanks! :smile:

You have been incredibly helpful too!

Best of luck for the exam and have a fantastic brrak afterwards

Reply 1885

NitroR

2

According to the mark scheme, you can measure the time it takes to decrease by some factor (e.g. 1/2, 1/e) over 2 different intervals (e.g. 5.0-2.5 and 4.0 to 2.0) and see if that time is the same - if so, it's exponential.

Reply 1886

blurred

8

For proper length equation, does it refer to the distance travelled by something or does it refer to the actual length of the object? I know in a rockets frame of reference, it travels a lower distance, but when the rockets length is measured by a stationary observer, its length is measured shorter than it actually is. Which of these scenarios does proper length correspond to?

Reply 1887

Original post by A-level2016

Unless for example they dont give a reading but say 1 div a particular scale is 0.1 then the uncertainty in one reading becomes +/- 0.05.
Think of this if i asked what the uncertainty in 2.106 it would be +/- 0.001 it won't ever be a (5) unless they state otherwise.

Ohh noes, I am now confused before the exam has started, I thought hhat the uncertainty in the reading of 2.106 would be +-0.0005 as it is a reading??????

Reply 1888

Original post by Rexar

Ohh noes, I am now confused before the exam has started, I thought hhat the uncertainty in the reading of 2.106 would be +-0.0005 as it is a reading??????

Remember when AQA just state values it's always +-1 in the last significant digit

Reply 1889

revisionphysics

10

If its a digital instrument you use the resolution as the uncertainty

if its analogue you use half resolution as uncertainty. and then if you need to make your own starting point you have to account for the start and end uncertainty
so it doubles.

is that right? i have been doing it like this and its been working

Reply 1890

Original post by Kyou

Remember when AQA just state values it's always +-1 in the last significant digit

Right. So if it said state the absolute uncertainty I would use +-0.001 but if it said state the oercentage uncertainty I wouod use +-0.0005 and then find the percentage uncertainty and give me answer to the same sig figs as in the question?

Reply 1891

Original post by Rexar

Right. So if it said state the absolute uncertainty I would use +-0.001 but if it said state the oercentage uncertainty I wouod use +-0.0005 and then find the percentage uncertainty and give me answer to the same sig figs as in the question?

No because in the spec paper for 15.7, 0.1 was used, not 0.05

Reply 1892

Remember this and you're fine. Unless stated otherwise, use this:

The value of the charge on an electron is given in the data sheet as 1.60 × 10^–19. In all such cases (when a value is given) assume the uncertainty to be ±1 in the last significant digit. In this case the uncertainty is ± 0.01 × 10^–19 C.

Reply 1893

Original post by Kyou

No because in the spec paper for 15.7, 0.1 was used, not 0.05

That was for the timing wasnt it, therefore yu take two reading, somit is 0.1.
But say for the voltmeter wuestion innthe same paper, 0.005 or something like that is used because it is digital or something???

Reply 1894