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June 25, 2019, 03:24:47 am

Author Topic: Physics sig figs  (Read 658 times)  Share 

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Ghost_

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Physics sig figs
« on: September 25, 2018, 01:48:51 pm »
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Hey,

I was wondering if sig figs are assessed in the exam, at least to the extend of chemistry where one mark is allocated to sig figs for an unknown question. If so, would they rather tell us in the question the number of sig figs required or is there a similar expectation as in chemistry because a lot of the trials I've seen don't follow the conventions either however it stated in last year's examination report that "Answers should be in decimal form and reflect the correct number of significant figures" so I'm a bit confused since I've heard different things on the matter.

-Thanks
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Bri MT

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Re: Physics sig figs
« Reply #1 on: September 25, 2018, 02:35:36 pm »
+2
From my understanding, in the exam it's best to use a common-sense number of figs. Eg. If theres only 1 sig fig of accuracy and you get the answer "250" write 250 instead of 3 * 10^2. If there are 3 sig figs of accuracy and you get "3.64231587374755..." write "3.64".  The most important thing here would be not writing "4" or "3.6" in that last example because I can easily see them taking marks off for that.

Hope this helps :)
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Ghost_

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Re: Physics sig figs
« Reply #2 on: September 25, 2018, 11:26:48 pm »
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Thanks miniturtle, that's what made sense to me too.
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S200

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Re: Physics sig figs
« Reply #3 on: September 26, 2018, 10:02:06 pm »
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what does 1 sig fig and 3 sig fig mean?
Basically, if I have a formula \(a\times b\), and \(a\) is given as \(1.4\), I can't get the answer anymore accurate than the \(1.4b\), because I don't know what \(a\) was before any rounding was done...

I personally suggest three significant figures if there is an issue...
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Bri MT

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Re: Physics sig figs
« Reply #4 on: September 26, 2018, 10:19:53 pm »
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significant figures or "sig figs" describe the accuracy of your result. For example, if I was to measure a table with a ruler I might say that it had a width of 62.5 cm and length of 212.7 cm. I wouldn't say that it had a width of 62.50000 cm, because that implies that I know it isn't 62.50005 cm or something. If I as then to calculate the area of the table top, I say that it was 1.33 m^2, not 1.329375 m^2  - because the numbers I was using to calculate were only accurate to 3 and 4 significant figures respectively.

examples
In 2.00 there are 3 sig figs
In 2.0 there are 2 sig figs
In  0.0001 there is 1 sig fig
In  0.00010 there are 2 sig figs
In 0.00101 there are 3 sig figs
In  100 there is 1 sig fig   (could also be 3 - this is one of the reason why scientific notation is good, it avoids this ambiguity)
In 100.0 there are 4 sig figs
In  101 there are 3 sig figs

When you multiply, the product should be written with the lowest amount of significant figures of the factors. Eg, 1.0 * 2.00 = 2.0
When you add, use the lowest number of deicmal places eg. 1011.000 + 2.0= 1013.0
« Last Edit: October 14, 2018, 09:21:48 am by miniturtle »
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minhalgill

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Re: Physics sig figs
« Reply #5 on: October 13, 2018, 05:34:24 pm »
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When you add, use the lowest number of deicmal places eg. 1011.000 + 2.00= 1013.0

is the lowest number of decimal places not 2 as 2.00 has 2, so shouldnt it be 1013.00 instead of 1013.0?

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Re: Physics sig figs
« Reply #6 on: October 14, 2018, 09:21:06 am »
+1
is the lowest number of decimal places not 2 as 2.00 has 2, so shouldnt it be 1013.00 instead of 1013.0?

Yep, that was a typo. Thanks for letting me know! 
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