Post by: ashwinkandel on October 02, 2010, 02:18:31 pm
Calculate the density of aluminium with its uncertainty. Express your answer to an appropriate number of significant figures.
density= ......................±................... g cm-3
Post by: elemis on October 02, 2010, 03:59:04 pm
Post by: elemis on October 02, 2010, 04:06:17 pm
adding the fractional uncertainties :
Hence, multiplying 1 and 2 gives an absolute uncertainty of 0.2
Therefore, ans =
Post by: Deadly_king on October 02, 2010, 04:10:07 pm
The mass of a cube of aluminium is found to be 580 g with an uncertainty in the measurement of 10 g. Each side of the cube has a length of (6.0 ± 0.1) cm.
Calculate the density of aluminium with its uncertainty. Express your answer to an appropriate number of significant figures.
density= ......................±................... g cm-3
hey that's fro, June 09 p2, right??
Anyway it's not that difficult. Let me get this clear for you.
Density = Mass / Volume ---> density = 580/63 = 2.685
Volume of cube = l3
Therefore density = m/l3
Delta D/density * 100 = delta m/mass *100 + 3deltaL/Length * 100
Delta D = [(10/580 * 100) + (3*0.1/6 *100) ] * 2.685/100 =0.18
Since all the values given were correct to 2 sf, your answer should be correct to 2sf.
Hence answer is 2.7 +- 0.2 gcm-3
Post by: elemis on October 02, 2010, 04:12:16 pm
Good work man ;)
Post by: Deadly_king on October 02, 2010, 04:12:45 pm
Well done Ari.....except that the units are g/cm3 :Pequation 1
adding the fractional uncertainties :equation 2
Hence, multiplying 1 and 2 gives an absolute uncertainty of 0.2
Therefore, ans =
Post by: elemis on October 02, 2010, 04:18:05 pm
Well done Ari.....except that the units are g/cm3 :P
I did that purposely because I wanted to see of you were paying attention :P
I was doing chem all this time..... concentrations and all :D
Post by: Deadly_king on October 02, 2010, 04:20:23 pm
I did that purposely because I wanted to see of you were paying attention :P
I was doing chem all this time..... concentrations and all :D
Haha........take it as if I believed ya :P
Yeah......i know you have loads on your head.....just chill and relax a bit dude :)
Post by: ashwinkandel on October 02, 2010, 04:38:20 pm
(answer 2.69 ± 0.09 g cm-3 scores 4 marks).
Can anyone teach me about the use of significant figures while solving the problems like the above one.
Post by: Deadly_king on October 02, 2010, 05:25:35 pm
i looked up the marking scheme. it was given like this:
(answer 2.69 ± 0.09 g cm-3 scores 4 marks).
Can anyone teach me about the use of significant figures while solving the problems like the above one.
Hmm.....this question carries 5 marks.
Ok........the values given to you and which you used in your calculations were 580g and 6.0cm.
In both cases the values were correct to 2 significant figures.
NOTE : The 0 in 580 is not considered as a significant figure but the one in 6.0 is considered as one. In decimals a zero in front of the other numbers is not considers as a significant figure (Example 2) but a zero after the decimal point which has a number in front is a significant figure.(Example 3)
Examples :
1. Express 5.89 correct to 2 sf ---> 5.9
2. Express 0.00875 correct to 2sf ---> 0.0086
3. Express 1.99 correct to 2 sf ---> 2.0
Hope it helps :)
Post by: ashwinkandel on October 02, 2010, 05:40:38 pm
Post by: iluvme on October 02, 2010, 05:42:38 pm
thanks for the info. but i have one doubt. how many significant digits are there in the digit 1.001010. and how do we know how many significant figures should we use in the question i asked.
6 significant figures. You ignore the last 0.
Usually its to 3.
Post by: Deadly_king on October 02, 2010, 05:44:34 pm
6 significant figures. You ignore the last 0.Indeed it is 6 :)
Usually its to 3.
Good job girl :)
+rep
Post by: iluvme on October 02, 2010, 05:49:42 pm
Indeed it is 6 :)
Good job girl :)
+rep
Thanks.
Isn't this like grade 5 math?
No offense meant to ashwinkandel.
Post by: Deadly_king on October 02, 2010, 05:51:07 pm
Thanks.Yeah......it's somehow similar though in physics it's much more complex ;)
Isn't this like grade 5 math?
No offense meant to ashwinkandel.
Post by: ashwinkandel on October 02, 2010, 06:13:22 pm
6 significant figures. You ignore the last 0.ending zero after decimal point is significant , isn't it?
Usually its to 3.
Post by: iluvme on October 02, 2010, 06:38:17 pm
Yes.
Post by: ashwinkandel on October 02, 2010, 06:56:10 pm
Post by: iluvme on October 02, 2010, 07:03:31 pm
if the last digit was significant then why did u say 6 s.f. there should have been 7 isn't it? and you have said ignore last 0. how can we ignore it if it is significant?
Damn.My mistake, No it is not significant. Sorry.
Post by: Deadly_king on October 03, 2010, 05:16:56 am
Damn.My mistake, No it is not significant. Sorry.Nope......ashwin is right there. Indeed the number is correct to 7 sf.
Since the zero has been written and is after decimal point, it is certainly significant.
Otherwise the last zero would not have been written to form a number correct to 6 sf.
I apologise for my mistake :)
Example : Express 1.99 correct to 2sf ----> 2.0
The zero counts as a significant figure.
I had already stated this example before :P
Post by: ashwinkandel on October 03, 2010, 01:26:51 pm
5 A student makes measurements from which she calculates the speed of sound as 327.66ms–1.
She estimates that her result is accurate to ±3 %.
Which of the following gives her result expressed to the appropriate number of significant figures?
A 327.7ms–1 B 328ms–1 C 330ms–1 D 300ms–1
Post by: elemis on October 03, 2010, 01:38:28 pm
Which year ?
Post by: ashwinkandel on October 03, 2010, 01:54:04 pm
Post by: elemis on October 03, 2010, 01:56:21 pm
ya it is D . Can you explain me how is it D?
I THINK this is the explanation :
Since the uncertainty is given to a maximum of 1 s.f. therefore the actual answer should also be given to an accuracy of 1 SF.
Hence, answer = D
What year is this question from ?
Post by: ashwinkandel on October 03, 2010, 02:12:02 pm
Post by: elemis on October 03, 2010, 02:30:42 pm
How could say I was correct ? My answer and explanation is wrong.
Post by: ashwinkandel on October 03, 2010, 02:38:07 pm
Post by: elemis on October 03, 2010, 02:39:20 pm
ohh i m really sorry. i apolologise for this i mistakely looked another marking scheme.
I'll be honest too... I really dont know how its C :P
Post by: Deadly_king on October 04, 2010, 05:31:41 am
one more question related to this:
5 A student makes measurements from which she calculates the speed of sound as 327.66ms–1.
She estimates that her result is accurate to ±3 %.
Which of the following gives her result expressed to the appropriate number of significant figures?
A 327.7ms–1 B 328ms–1 C 330ms–1 D 300ms–1
Let delta C = c where C is the speed of sound.
% uncertainty = c/C * 100
3 = c/327.66 * 100 ---> c = 9.8
But c is taken as 10 since the % uncertainty (3%) is given correct to 1 significant figure.
Therefore the correct answer should be to the nearest tenth which results in C = 330 m/s
Hope you understood what I am trying to say :)
Post by: ashwinkandel on October 04, 2010, 12:50:11 pm
Post by: Deadly_king on October 04, 2010, 01:08:39 pm
you are great deadly_king. thanks again .No problem dude :)
By the way I noticed you added me on msn ;)