# Physics Paper 5 tips

Discussion in 'International A And AS Level' started by arlery, Apr 3, 2012.

1. ### arlery

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Hey,
Erm so I was looking up threads that might actually help in Paper 5 [considering I have my mock exam tomorrow] but I couldn't really find one, so decided to post one.

Things You Should Know For: Design, Analysis and Planning

VARIABLES
Scientists use an experiment to search for cause and effect relationships in nature. In other words, they design an experiment so that changes to one thing causes something else to vary in a way that the scientist can describe as a 'trend'. The most useful way to describe a trend is a mathematical one.
These changing quantities are called variables, and an experiment usually has three main kinds: independent, dependent, and controlled.

*The independent variable is the one that is changed by the scientist. In an experiment there is only one independent variable. This is usually plotted on the X-axis of the graph that the scientist uses to display his/her results in.
As the scientist changes the independent variable, he or she observes what happens.

*The dependent variable changes in response to the change the scientist makes to the independent variable. The new value of the dependent variable is caused by and depends on the value of the independent variable. For example, if you turn on a water tap (the independent variable), the quantity of water flowing (dependent variable) changes in response - the water flow increases. The more open the tap - the faster the flow of water. The number of dependent variables in an experiment varies, and there is often more than one.

*Experiments also have controlled variables. Controlled variables are things that would have an effect on the dependent variable. S/he must be sure that the only thing affecting that variable is his/her adjustment to the independent variable.
So, controlled variables are quantities that a scientist needs to keep constant, and s/he must observe them as carefully as the dependent variables.
For example, if we want to measure how much water flow increases when we switch on a tap, it is important to make sure that the water pressure from the water supply (the controlled variable) is held constant. That's because both the water pressure and the opening of the tap valve have an impact on how much water flows. If we change both of them at the same time, we can't be sure how much of the change in water flow is because of the faucet opening and how much because of the water pressure.
Most experiments have more than one controlled variable. Some people refer to controlled variables as "constant variables."

*INTRODUCTION
Whenever you design an experiment you have to first 'set the scene'.
You are not ever finding anything out without any preconceptions. You always have ideas about what you are going to find out - you have expectations!
In a science experiment these expectations will be based on:
- what you have experienced in life,
-experiments you have carried out before and
-scientific knowledge (things you have been taught about science at school, or have found out from books).
*In your report you need to explain to the reader what you expect to find out and why!
*You do not have to look into a crystal ball and write down numeric predictions... just predict a general trend. A good way to do this is to sketch a graph!
*You do have to explain the main scientific ideas that your prediction is based on. Try to use scientific keywords in this section and explain in simple terms what you understand them to mean.

A Fair Test
A fair test situation is vital for an investigation's results to be meaningful. You therefore have to use the scientific knowledge you have explained to identify the variables in your investigation - things you have to control, otherwise it will not be a fair test. Say what will need to be controlled and why - using theory to explain it.
One of the variables will be the variable you are going to change. Say which on you are going to change and by how much (the range over which you will change it). Say how you found out that was a suitable range. It may well be your preliminaries that helped you decide on a suitable range! Then say have you are going to control all of the others you have identified.

You will have a rough idea of what you want to do, but will need to 'tweak' your idea by trying things out practically. You therefore sketch out a rough experimental procedure and test out the best way to do it in a preliminary session.You may want to:
- choose materials to work with: check that you will get a big enough range of readings with the ones you have chosen to investigate.
- find out if you are controlling the other variables well enough to have a 'fair test'.... maybe you will spot some you hadn't thought of!
- practise using the equipment, and see if you need to make adjustments to avoid or minimize errors.... or make it safer!
- spot dangers in your procedure that you ought to avoid.

Always check with a teacher before you carry out preliminary experiments - they have more experience at spotting potential dangers than you do!!
Remember to say in your report if you found out a better way to do it from preliminary work.... and how you checked your ideas were sound before proceeding.

.

3. ### arlery

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*PROCEDURE

The procedure has several parts to it:
*A fully labelled diagram of the experimental equipment.
This should be so detailed that a person could carry out the experiment just from the diagram! It must be fully labelled with specifications of the equipment (e.g. '250 ml beaker' rather than just 'beaker'). Measuring instruments must have their range as well as increments marked on them (e.g. rather than 'thermometer' you would put a mercury filled thermometer with a range of -10oC to 110oC in 0.5 oC increments) A full side of A4 should be given to this!
*A full list of equipment - including minor parts
This should be done on a separate sheet of paper as a list to be given to a technician. Full specifications of the equipment (e.g. '250 ml beaker' rather than just 'beaker') must be requested. Measuring instruments must have their range as well as increments marked on them (e.g. rather than 'thermometer' you would put a mercury filled thermometer with a range of -10oC to 110oC in 0.5 oC increments). Odds and ends such as: 4 connecting wires, 2 crocodile clips, sellotape etc. must be itemized.
*A risk assessment
List all of the possible hazards you have identified and how you intend to avoid them.
*A set of instructions
These should be in past impersonal tense.... 'The apparatus was set up as shown in the diagram. The beaker was filled with 100 ml water..... etc.'. This is far better than a list of instructions with bullet points - but you may want to start off with such a list and then translate it into the correct form of English for scientific writing. The order must be logical!Don't forget to say that the experiment was repeated, how many times it was repeated etc. Remember to say that results were recorded - in a table of whatever, averaged, and that a graph was plotted.

*RESULTS/ANALYSIS
When successive measurements of the same quantity are repeated there is a distribution of values obtained. In experimental physics it is vital to be able to measure and quantify this uncertainty. The words "error" and "uncertainty" are often used interchangeably by physicists - this is not ideal - but get used to it!
Some important questions can only be answered if, in addition to performing an experiment, an error analysis has been conducted. These include:
• Do the results agree with theory?
• Are they reproducible?
• Has a new phenomenon or effect been observed?
*Types of Error

We need to identify the following types of errors:
• Systematic errors - these influence the accuracy of a result
• Random errors - these influence precision
• Mistakes - bad data points.
*Accuracy and Precision

These are two terms that have very different meanings in experimental physics. We need to be able to distinguish between an accurate measurement and a precise measurement. An accurate measurement is one in which the results of the experiment are in agreement with the ‘accepted’ value. Note this only applies to experiments where this is the goal – measuring the speed of light, for example. A precise measurement is one that we can make to a large number of decimal places.

*ERRORS
These cause reading to be different from the true value. For example; Error is a measure of how close you can be sure about your measurement.
Percentage error = (smallest measurement you can measure/your measurement)*100
e.g. a ruler in mm divisions measure
es a length of 10 mm. The smallest
that the ruler can measure is to within 0.5 mm. So the error in my
measurement of 10mm is;
(0.5 mm/10 mm ) x 100 = 5%
This means I have measured 10 mm +/- 5%
The measurement may actually have been as big as 10.5 mm or as small as 9.5 mm.

*Types of Errors

- Random
Random errors may be detected and compensated for by taking a large number of readings.
For example: Random errors may be caused by human error, a faulty technique in taking the measurements, or by faulty equipment. These cause readings to be spread about some value other than the true value; in other words, all the readings are shifted one way or the other way from the true value.
- Systematic
These cause readings to be spread about some value other than the true value; in other words, all the readings are shifted one way or the other way from the true value.
- Zero
For example: A zero error occurs when a needle on an ammeter fails to return to zero when no current flows, or when a top-pan balance shows a reading when there is nothing placed on the top-pan balance

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4. ### XPFMemberXPC ModeratorStaff Member

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Assalamoalaikum wr wb!

say you are taking log of x...
now x is suppose.. 83 +/- 5...
log 83 = 1.92
so Upper Limit (UL) = 83 + 5 = 88
and lower limit (LL) = 83 - 5 = 78
find log of (UL-LL)/2 = (88-78)/2 = 5
log 5 = 0.70 => This is the uncertainty...
so log(83 +/- 5) = 1.92 +/- 0.70

Sorrydid a mistake in the method I mentioned ealier...
this is how we proceed..
[log(UL) - log (LL)]/2

Check smzimran's post below..he has a different method...
this is the way we were taught...

Hope this helped..!

5. ### smzimran

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Thanks a lot arlery!

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6. ### smzimran

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I think there is a problem here!
the uncertainty cannot be such high compared to the actual value
% error = 0.70 / 1.92 * 100 = 36.5%
% error in actual question is = 5 / 83 * 100 = 6.0%
That is why this method is incorrect.
The correct method is:

now x is suppose.. 83 +/- 5...
You can work either with upper limit and mean value (88 and 83)
OR
You can work with mean value and lower limit (83 and 78)

I will go with the former (88 and 83)
the uncertainty is = lg 88 - lg83 = lg (88 / 83) = 0.025

If I work with mean value and lower limit (83 and 78)
the uncertainty is = lg 83 - lg78 = lg (83 / 78) = 0.025

log(83 +/- 5) = 1.92 +/- 0.025

I have attached two snapshots frm a book sorry for the bad quality
I took these frm my phone camera!

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7. ### ABDSyed

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AOA
Thanks A Million Bro
Jazzallah Ba Khair

8. ### smzimran

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U r welcome!
Wa iyyakum

9. ### arlery

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np!
and thank YOU for the calculation part correction!

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10. ### XPFMemberXPC ModeratorStaff Member

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oops...yeah...sorry... i mixed the things

i'm gonna edit my post...inshaAllah..
so yeah it is...[log(UL) - log (LL)]/2

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11. ### XPFMemberXPC ModeratorStaff Member

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smzimran..u used a different method...your teacher told you this?
Anyway we did i this way the one I mentioned above...
I guess both are correct...

12. ### smzimran

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Yes my teacher told me and i also saw this in the book of which i have posted snapshots
= [log(UL) - log (LL)]/2
^This is also correct!

We can further modify it using a little knowledge of logarithms and it becomes
= 0.5 lg (UL / LL)

Btw, i feel the method i used is easier as you just have to find the UL and not both UL and LL
My formula:
= lg (UL / RL)
*RL means real value

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13. ### hassam

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well/....i ll want to add one thing that u can either use upper value or lower one....its better to use the one that givves the largest deviation and that always comes with lowest value(cn be visualised by looking at shape of log graph)....
and can u please tell what was that bit about significant figures in log quantities....

14. ### bineetojha

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15. ### h.alia

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does anyone have bio paper 5 notes ??

16. ### SkyPilotage

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Awesome, it has been very helpful. Thank you very much!
1-) May you please shed light on the number of decimal places and significant figures? How can we know how many to use? Whats the relation between them?
2-) For Question One, do we have to look for experiments on all the Physics Chapters? Because we need to know what kind of experiment to set up.
3-) Can an ideal answer be going like this for Question 1 :- ?
The independant variable is ... and the dependant is ..... The variable that need to be controlleed are....
Then talking about the procedure, results and safety.
My point is Can we address the points that the examiners are looking for directly in the same order or do we address the questions posed in the question in that same order?
For Example :-
A question part asks :- a) the procedure to be followed
etc...
Do we state the procedure directly or do we address the points the examiners are looking for? Meaning do I Identify the variable first then state the methods of collecting data then analysis then safety?

Thank you for your time ,

17. ### user

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AsSalamoAlaikum wr wb!

For significant figures...check the content for paper 5 given towards the end of the syllabus...! do go through all those things...

and I follow the marking order rather than the question...
and additional details...i add it in the method part...like write the method part including every minor detaill...and that usuall covers those additional points

18. ### SkyPilotage

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just went through it, nothing related to d.p and s.f of absolute errors :S

19. ### SkyPilotage

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Im just feeling that you surely require prior knowledge of experiments for question one in paper 5.
To investigate force and acceleration, who would think of an air glider track !
Projectile motion, wooden board with a small ramp on a side.. its hard to think of such experiments without having prior knowledge in the exam.
Investigating polarisation, or an a.c voltmenter (signal generator + cro) , etc.... Lots of prior knowledge of experiments required...
Thats the only thing that is worrying me about Paper 5.... that they may ask for an experiment where I have no idea how to perform it... that will cost be 15 marks ..

20. ### smzimran

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Didnt you give practicals last year in AS ?

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