Which number to use?

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604601071
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Joined: Fri Sep 25, 2015 3:00 am

Which number to use?

Postby 604601071 » Fri Oct 09, 2015 6:26 pm

When it comes to constants, the textbook flips between numbers like: c= 2.998 x 10^8 and 3.0 x 10^8 all the time, which ones should we be using? How many sigfigs for each constant?

Hanna Barakat IL
Posts: 12
Joined: Fri Sep 25, 2015 3:00 am

Re: Which number to use?

Postby Hanna Barakat IL » Fri Oct 09, 2015 6:29 pm

Both should be fine. I'd generally stick to using the same amount of sig figs as the rest of the problem asks for. It's such a minute difference though, that when you do round off at the end, it shouldn't effect your final answer. I'd email your TA just to be sure. :)

Vanessa A 3F
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Re: Which number to use?

Postby Vanessa A 3F » Sat Oct 10, 2015 2:51 pm

Our reference sheet says c= 2.99792 x 10^8 m/s, so I'd use as many sig figs as possible, like 2.998 x 10^8 just to be safe and as precise as possible. Try a problem where you use 3.0 x 10^8 and do it again using c=2.998 x 10^8 m/s. As you'll find, the answers are slightly different, but if your final answer only requires a couple sig figs there's no difference.

Kaitlin_Ryan_ 3K
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Joined: Fri Jul 15, 2016 3:00 am

Re: Which number to use?

Postby Kaitlin_Ryan_ 3K » Sun Sep 25, 2016 5:40 pm

When dealing with known constants such as the speed of light, I tend to use the number with the most number of significant figures. This allows for fewer errors due to rounding off. I would therefore use 2.998 x 10^8 when possible, unless the problem specified that the speed of light was 3.00 x 10^8 in order to minimize rounding errors.

Chem_Mod
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Re: Which number to use?

Postby Chem_Mod » Sun Sep 25, 2016 11:09 pm

Good discussion on Chemistry Community tonight.

Correct sig fig will vary.

However, in a test I provide all students with the same constants, equations, and periodic table.
Therefore all students should have the same answer if sig-fig and round-off are done correctly.

Please do not email your TA (my TAs) science questions.
Use Chemistry Community :-)

Jazmin Martin 1D
Posts: 19
Joined: Fri Dec 04, 2015 3:00 am

Re: Which number to use?

Postby Jazmin Martin 1D » Mon Sep 26, 2016 11:04 am

Will we be knocked off major points if we are off by a sig fig?

emilyharland
Posts: 22
Joined: Fri Jul 15, 2016 3:00 am

Re: Which number to use?

Postby emilyharland » Tue Sep 27, 2016 1:56 pm

When doing calculations, use as many sig figs as possible up until you have calculated your final answer, which should include the same amount of sig figs as the smallest numerical data being used. For instance if the smallest number in the original data has only 3 sig figs, then in your final answer you should only have 3 sig figs, and you should be correct.


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