BIOLOGY practicals help

[paridhi shobhana]

wat was ur x and y axis ??? time in X and the conc in y ryt

Yess changing the time was the independant variable so it propably should be on the x-axis !

THANKS !!!!! :Rose: :good:

 

[holychalice]

wat was ur x and y axis ??? time in X and the conc in y ryt

Yess changing the time was the independant variable so it propably should be on the x-axis !

THANKS !!!!! :Rose: :good:

wasnt time the dependent variable ?? and concentration the independant varible cuz increaseing the conc would cause lesser time to produce 1dm3 solution ?!

 

[Emily793]

no since each time you are closing the tap a bit tighter thus incresing time for collection of protein since the more you close the tap the more difficult it is for the solution to pass through thus more time taken.
i too had this doubt in exam took me about 10min to decide which variable was which...

 

[mrpaudel]

my drawing is wrong too emily

and my teacher said that the percentage error is 3.33%

and i ve got the U between 5% and 50% and my friends got it between 5% and 0.5% but my teacher said
the examiner will not deduct marks as the conc of U depends on what u ve written in the table

I got the answer 3.33 too, but I just wrote "3" i think they will defintly deduct marks for this!

error is 13.3%....i dont know how ur teacher said its 3.33% ...may b m wrong too...!!

 

[mrpaudel]

Are'nt we suposed to do 1/15 for error? Since we are recording time twice??
What differences did u put guys? I put projections one was circular shape and the other rectangular. Fig 2.2 was larger in size, and the layer y or x dnt remember what i wrote was thicker in 2.2, there was also taste buds in 2.2 and nt 2.3

yeah...rest was same as mine..the 1st one is also the same..but this is how i wrote...... Fig 2.2-->has longer projections and flat at the end........fig 2.3--->has shorter projections and spherical at the end..>!!

 

[mrpaudel]

Time was independent..so it should b on X axis for sure.....coz, the concentration collected down there depends on the time u allow the thing to pass through...!!

 

[mrpaudel]

And guys....this is what i did for error one...

Initial time = (0 ± 1) s Final time= (15 ± 1) s

so....time taken =(15 ± 2)s....so uncertainty=2/15 * 100% giving u 13.3% ( well..i read the least count need to b halved to get an error in Mary JOnes book........but....in some year past paper, the error was the least count itself....!! which was written in ms...so i thought to follow the ms..so put the error as 1 rather than halving to get 0.5 !!...and...while getting the difference, u must add error which means...2...so..i got 13.3% ....now if u think m incorrect smwhere..correct me guys..!

 

[nano9595]

no it is supposed to be the uncertainty /15*100
and in this case the lowest count was 1s and so the uncertainty was 0.5s
and so the calculation must be like this: 0.5/15*100
thats what i think and could u pls send me the link of the ms that you ve mentioned above
cause i think u ve misunderstood the ms as there are exceptions where u have to take the lowest count without halving
it like when using a burette or a dropper

 

[mrpaudel]

no..its was in a ruler...!! well..i wil definitely put the link here..if i find it..!! will search it later..and put it here...!! but...u are wrong for sure..>!! even if uncertainty is 0.5 u have to add the error to get 1....!! as i did..!! u have to put 0.5 where i kept 1 and..put 1 where i said it should be 2...!!

 

[mrpaudel]

that question : http://www.xtremepapers.com/CIE/Interna ... _qp_33.pdf


ms for that question: http://www.xtremepapers.com/CIE/Interna ... _ms_33.pdf


1 (f) number...!!

 

[nano9595]

in the ms he didnt add anything nor he did anything of what u ve mentioned above and the answer is not the least count itself
the least count is 0.1 cm and halving it would give
0.05 cm that what is in the ms

sorry :sorry: but i cant understand ur point what do u mean by adding the error

maybe ur right but i cant get ur method after all this question was only worth 2 marks do u think that the
examiner would grant me a mark for my working?
could u pls explain it to me
thnx :Rose:

 

[paradoxice]

@mepaudel,this question http://www.xtremepapers.com/CIE/Interna ... _qp_33.pdf
is error on a ruler.. But the question that came out about percentage error is error in time and not on a metre rule..actually when calculating error in time,errors come from reaction time error which lies between 0.1 till 0.4 and not human error.. hence,you should use any value between these reaction time error and calculate percentage error,i did (0.1/15)X100 and the answer is 0.666 which is 0.67% . hope that could help you..

 

[mrpaudel]

@mepaudel,this question http://www.xtremepapers.com/CIE/Interna ... _qp_33.pdf
is error on a ruler.. But the question that came out about percentage error is error in time and not on a metre rule..actually when calculating error in time,errors come from reaction time error which lies between 0.1 till 0.4 and not human error.. hence,you should use any value between these reaction time error and calculate percentage error,i did (0.1/15)X100 and the answer is 0.666 which is 0.67% . hope that could help you..

as far as i m concerned...its in second...so while that needle moves, it doesnot more than a second....therefore, i wrote
INitial timing =(0±1)s and..final timing=(15±1) s ......so time taken is 15 seconds..with error of 2s...>!! therefore 2/15*100...thats what i did..!! i dont know the rest..!!


well..for the query bout the ruler and percentage error...well.........percentage error= error/ measured value *100%.....well..if percentage error was asked in tht ruler..it would be 0.05/ measured value with that ruler * 100%....

 

[mrpaudel]

in the ms he didnt add anything nor he did anything of what u ve mentioned above and the answer is not the least count itself
the least count is 0.1 cm and halving it would give
0.05 cm that what is in the ms

sorry :sorry: but i cant understand ur point what do u mean by adding the error

maybe ur right but i cant get ur method after all this question was only worth 2 marks do u think that the
examiner would grant me a mark for my working?
could u pls explain it to me
thnx :Rose:

can u plz look at it once...there are 20 divisions in 1cm..which means...1 division=0.05cm...i think m correct...!! so the same is written as error..!!

 

[nano9595]

ohhh yeah sorry my bad :sorry: :fool:
didnt count those divisions i thought that there were 10 divisions
now i get ur point however in our exam it was a stopwatch not a ruler
so why r we arguing about the ruler? :unknown:

 

[mrpaudel]

well...i didnot say m correct....!! but i read like this..in Cambridge International Biology by Mary Jones, who is a senior xaminer in Cambridge...!! error should b added...i wrote that one...!! well...error in ruler or the stopwatch.......the rule is same i guess....!! ..but the xample given in that book was Thermometer...!! well..whatever it is, leave it...!!

 

[nano9595]

what do u mean by adding the error ? :unknown:

 

[paradoxice]

I assure you guys.. there is no such thing of adding error..this is done when calculating uncertainty in physics.. it's completly different when calculating percentage! And futhermore,error in a stopwatch anything in time are reaction time error.. it is not the same as a metre rule..

 

[mrpaudel]

@paradoxice: well dude, this is for u..!! this is written in the book of biology...Written by mary Jones....senior xaminer of Cambridge...!! so i dont know whats correct....i just said what i read here..so this is the source...!! if m right, it will help u....if i failed to get the correct info from here, i will learn the correct thing..!! so...not a prblm..but just check it out once....

 

[paradoxice]

yeah marui jones said the right thing.. i can see that.. but this applies for a thermometer
If could understand what i mean..Error in time is different with error in a thermometer.. in a thermometer when you take readings do you hae to start or stop something taking time?? its different. as for measurment in time it took 0.1 to 0.5 seconds atleast for you to start or stop the stopwatch. and this is what is called reaction time!