IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: [Spy] on May 20, 2010, 09:47:27 am
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- Read through past paper experiments, get an idea of what the questions come like.
- when taking values off a stopwatch for example, you should write the timing to the resolution of the stop watch, meaning if the time recorded was 00:06:42, then you write it was 6.42 and not 6.4, even if it was 00:06:00, you still write it as 6.00. these are called RAW VALUES.
- when doing calculations involving raw values, you should always keep them to the same significant figures are the raw values, and yes its very important, examiners care alot about these stuff in practicals unlike other papers.
- when doing your axes values, dont just think that if you get all your readings within the range then you managed to get a good axes no! you need to make sure than each tiny square will give you a value easy to deal with for example 0.2 or 0.15 even but not something recurring like 0.3333333 for example.
- when drawing graphs, make sure your curve/line covers more than half and preferably 80% of the graph provided.
-when plotting a graph us X and not a dot with a circle around it.
- never ever has it been obvious that you need to draw a curve, and most most most of the times its a line of best fit.
- your line of best fit has to go through the most points and should the same number of points on both sides and they should be equidistant from the line.
- when finding gradient, it is preferable if you use one of your plotted points which the line cuts, and therefore always try to make that the last and first points are on the line
- if for example your asked to take readings for a pendulum swing at a range of length from 0.3 to 0.6, then YOU SHOULD TAKE A VALUE SLIGHTLY LOWER AND A VALUE SLIGHTLY HIGHER like 0.25 and 0.65.
- when constructing the table, you should always have the name of the reading and its unit for example time/s or length/m
- also when doing your table record two readings, name them t1 and t2 for instance and then find the average. and use the AVERAGE when plotting.
- if you are asked to find a thickness of a wire for example, measure its thickness at diffident places and take the average.
thats what i have :)
i hope you find it useful and if anyone has anymore please share them
good luck :D
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nice,man.
+rep. :)
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your welcome :)
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thanks a lot. really helpfull. :)
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my pleasure :)
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- if for example your asked to take readings for a pendulum swing at a range of length from 0.3 to 0.6, then YOU SHOULD TAKE A VALUE SLIGHTLY LOWER AND A VALUE SLIGHTLY HIGHER like 0.25 and 0.65.
i didnt get this one? :S
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lets say the expirment involves taking time readings for how long it takes the pendulum to come to rest, then they may tell you to repeat the experiment with different lenghts of the wire holding the bob, for example 0.3 to 0.6, then start with values a bit lower than those
get it?:)
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ohh ohkay...buh why do we take .5 lower n higher than the range..?? to get set of six readings?
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no, you can take any six readings between, but because thats it, you should take a bit lower or at least take the values themselves so that they are included, and you could take less to see it how it compares with lower values
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thank you =)
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Hey s3 guys my sir said that 2 ques r coming, i can tell buh if u the moderatrs allow?
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for variant 1, its a pendulum question and a long electricity question.
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n i heard its sumthin to do with ball slidin down an inclined plane...
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Wat about varient 2?
@spy acc to my kolege news any 2 of the folowing r coming
--> electricity
visosity, its somethng about oil n water
or, pendulum
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what u guys doing pp 33 or 34
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im doing 31
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Thanks spy!!
really appreciate it but i still don't get why do we take lower values?? reduce experimental errors..do we include them in our table??
plz explain further....Thanks and By the way +rep
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Your Welcome Mate :)
if you look at the past papers, they often ask you to repeat the experiment with different values of a specific factor, length of thread/resistance for example. you should take a value just a bit lower so you'd see how it compares. and to have that value included in your readings. and By the way YOU SHOULD ALSO INCLUDE THE EXACT HALF WAY READING For example if the range given is 0.3-0.6 then you must include 0.45, yeah its not just anything you have to include specific things.
what do you mean "reduce experimental errors..do we include them in our table??"
thanks :)
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i mean that if they ask us to take the lengths between 0.3 and 0.6, right u said to take 0.25 and 0.65, so do we include the 0.25 and 0.65 in our table of results or we include 0.3 and0.6 although we have used 0.25 and 0.65??
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no no, you take six readings for example or whatever they ask you and you include this as a standard.
0.25
0.30
0.45
0.55
0.60
0.65
i included a value lower (25) a value higher (65) a value in the middle (45) and the values they asked for (30 and 60) you can include any number as a sixth preferrebly above the half
:)
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r u sure about it?? From where did u get this info??
it will be very useful if u can post the source of this info ;)
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my teacher, and he's been teaching a levels for 12 years. so i'd trust his word, and besides it sounds very logical, you can at least only use the actual values (0.3 and 0.6) but you should use the middle value.
:)
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THANX LOADZ :D
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your welcome :D
where's the +rep? :P
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- also when doing your table record two readings, name them t1 and t2 for instance and then find the average. and use the AVERAGE when plotting.
can u elaborate this ?
what is t1 and t2
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your welcome :D
where's the +rep? :P
i did give u one but dunno y not appearing
anywayz i'll give u another 1 after 2 hours have passed :D
listen do u noe how to calculate the uncertainties?? ???
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lets say you have to record the time taken for a pendulum to stop swinging, you should repeat each twice for each length..
for example, your recording the time taken for a 0.5 meter pendulum to stop, then you time it once, and twice. you get 10.51 and 10.75 then find find the average and use this as the time value for the length of 0.5 meter :)
then do the same for your other lengths
hope its clear? :)
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i did give u one but dunno y not appearing
anywayz i'll give u another 1 after 2 hours have passed :D
listen do u noe how to calculate the uncertainties?? ???
oh probably takes time to show, haha thanks :D
yeah its easy, the key is you ALWAYS add them, and they should be in PERCENTAGE Form. these two things are very important.
for example lets say you have the equation.Q=A*B^2 all over C^1/2
and A=1.3mm +/- 0.02
B= 2.8mm +/- 0.01
C= 0.8mm +/- 0.008
convert all to percentages first! for example A= 0.02/1.3 * 100 and do the rest for B and C
lets say for example you get A=1% and B=2% and C=1% (im too lazy to calculate :P)
so you plug them into the equation.
AND YOU ALWAYS ADD. but before that, any thing to the power of X, in uncertainties you multiply by the power. (because your adding them twice for instance if its squared you multiply by 2)
so for our equation. its 1+(2*2*(the power)) + 1*0.5(the power) as you can see its always ADD no matter what the equation is.
so your uncertainty is 1+4+0.5=5.5%. and if you want to find it as a value of the actual result. then use this equation. X/the value= 5.5/100
i hope its clear :D
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oh probably takes time to show, haha thanks :D
yeah its easy, the key is you ALWAYS add them, and they should be in PERCENTAGE Form. these two things are very important.
for example lets say you have the equation.Q=A*B^2 all over C^1/2
and A=1.3mm +/- 0.02
B= 2.8mm +/- 0.01
C= 0.8mm +/- 0.008
convert all to percentages first! for example A= 0.02/1.3 * 100 and do the rest for B and C
lets say for example you get A=1% and B=2% and C=1% (im too lazy to calculate :P)
so you plug them into the equation.
AND YOU ALWAYS ADD. but before that, any thing to the power of X, in uncertainties you multiply by the power. (because your adding them twice for instance if its squared you multiply by 2)
so for our equation. its 1+(2*2*(the power)) + 1*0.5(the power) as you can see its always ADD no matter what the equation is.
so your uncertainty is 1+4+0.5=5.5%. and if you want to find it as a value of the actual result. then use this equation. X/the value= 5.5/100
i hope its clear :D
didnt understand anything!!! ;D
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HAHAHAHAHAHAHA NASHAT, GO STUDY
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ok for uncertainties check this link
http://spiff.rit.edu/classes/phys273/uncert/uncert.html
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HAHAHAHAHAHAHA NASHAT, GO STUDY
im trying, but physics is just tooo hard!! i dont understand anything!! :( ::)
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hahahahahahhaa stop fooling people here, you dont take physics. go study A2 chemistry and get raped ;)
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hahahahahahhaa stop fooling people here, you dont take physics. go study A2 chemistry and get ****d ;)
i will study chem A2, but right after im done with understanding physics
its just confusing :S
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stop -.-
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stop -.-
im serious!! ask me any question and i will answer :)
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what came in the exam?
:P
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what came in the exam?
:P
path difference and speed of waves and all the other stuff about velocity, voltages, etc.
good enough? :)
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No, not a single question about path difference. haha nashat stop convincing me that you take physics. im with you in class are you that stupid? haha
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No, not a single question about path difference. haha nashat stop convincing me that you take physics. im with you in class are you that stupid? haha
i took tution for physics because it wouldve clashed in the school timetable with BIO A2!!!now just ask a question and lets see if i answer or not!
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how do we calculate uncertainties when weve taken readings using screw guage and vernier calliper
Thanks
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hiii .. i hv a question .. like the one in m/j 09 Q1-d .. hw we suppose to find P and Q .. >:(.. if any can help me :)
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Paper 3? What Variant?
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m/j 09 .. ppr 31
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hiii .. i hv a question .. like the one in m/j 09 Q1-d .. hw we suppose to find P and Q .. >:(.. if any can help me :)
wht the hell r u talking abt, there is no 1-d
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wht the hell r u talking abt, there is no 1-d
sorry my bad, i thought u were talking abt igcse
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m/j 09 .. ppr 31
1/I=R/P+Q/P
change it into a straight line equation form (y=mx+c) and then just put in the values you got for the gradient and y-intercept. try doing it that way yourself and then if you couldnt ill do it for you :)
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so wat is excpected to come for 33?
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Here's another tip guys, generally for all practicals.
when your doing the first question, try finishing it 5-7 minutes earlier,so you can get to read the second question while the others are still doing the first. it helps ALOT! cause you'll go to the second question knowing directly exactly what to do unlike the others which will take some time to grasp the experiment first. just dont RUSH the first question,
i did it in biology practical and i was on of the few who found it very direct ;)
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1/I=R/P+Q/P
in y=mx + c ... so c = Q/p and mx = R/P ?? m i ryt or wt ?
thanks alot spy
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yeah c=q/p
but, for mx, you can split R/P into, 1/P * R/P, so m=1/P (and x=R/P)
no problem :)
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bt in this question .. x=R nt R/P
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why?
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cuz in the graph the x-axis is R
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no leave the graph, just compare the equations.
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hmm i ddnt gt it >:( then hw ill substitute ??
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spy .. i think x=R cuz only in this way we can substitute the values to find P
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How about the last part of ques 2? The 8-point question about errors and how to fix. I always lose mark in that ques.
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hey, can anyone please post the possible errors and improvements for tomorrow's phy 33? any ideas, spy?
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It All Depends on the expirement, but here are some standard ones.
Repeat experiment several times and take average.
avoid paralex error by reading off a ruler in line with the value on the ruler.
use a set square for anytime you need to ensure right angles or measure something vertical.
if you tell me a specific experiment in a past paper or something i can tell you some which are more specific :)
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if you tell me a specific experiment in a past paper or something i can tell you some which are more specific :)
[/quote]
s07, paper 5...question 1...i know, we dont have paper 5 in AS but if a similar kind of experiment comes, then what could be the possible errors and improvements?
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which part exactly?
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dude this is paper 5, its analysis, meaning your set up the expriment yourself, we dont have anything like this in AS, its just a practical and you follow instructions given to you. i cant tell you anything about it because its an A2 paper and i dont know anything and you dont need to know it because we arent getting anything like it :)
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hii... can any1 tell me wts least count .. and percentage uncertainty ??
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like the one in o/n 07 question 2-c
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Hi
if i was asked to calculate the gradient and y-intercept from the graph should i convert the plotted values to their base units in order to get the right values of the gradient and y-intercept???????????
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spy .. help meeee !!! percentage uncertainty o/n 07 Q2-c .. and the least count
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NO CHEATING WE ARE WATCHING YOU ALL !!!!!!!!!!!
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EXCUSE ME I WAS NOT CHEATING because IF U SAW MY PREV POST I WAS ASKING FOR HELP ABOUT THE QUESTION I JUST ASKED ABOUT THE Y-INTERCEPT AND GRADIENT PLZ RESPECT THT I AM SO TENSED ND NOT IN THE MOOD FOR YOU TO REMIND ME THERE IS NO CHEATING