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### How many significant figures?

Posted: **Sun May 06, 2018 11:02 pm**

by **Isabel Jabara 1C**

On one of the UA's practice tests (Lyndon's), question 7a asked "An excited hydrogen atom undergoes an electronic transition from n=3 to n=1. Calculate the frequency of the photon emitted." Since the question only contains numbers with 1 significant figure, should we answer with only one?

### Re: How many significant figures?

Posted: **Sun May 06, 2018 11:05 pm**

by **Elijah E 1C**

Since these numbers reference atomic energy level and cant be any non-integer I don't think they effect sig figs. That being said I would give the exact value.

### Re: How many significant figures?

Posted: **Sun May 06, 2018 11:05 pm**

by **danielruiz1G**

Just remember to use the rules of sig figs when either multiplying/dividing or adding/subtracting. With multi./division you keep the same number of digits as the smallest number of sig figs in your problem and for addition/subtraction, you keep the sig fig until the digit of the least accuracy.

### Re: How many significant figures?

Posted: **Sun May 06, 2018 11:06 pm**

by **Chris Qiu 1H**

I'd keep 3-4 sig figs just to be safe. Having only one sig fig for a value that wont be a whole number (or a single digit for that manner) doesn't make too much sense.

### Re: How many significant figures?

Posted: **Mon May 07, 2018 3:05 pm**

by **Chem_Mod**

Isabel Jabara 1C wrote:On one of the UA's practice tests (Lyndon's), question 7a asked "An excited hydrogen atom undergoes an electronic transition from n=3 to n=1. Calculate the frequency of the photon emitted." Since the question only contains numbers with 1 significant figure, should we answer with only one?

Use the number of sig figs given by the constants that you used. For example, planck's constant will be given with a certain number of sig figs.

### Re: How many significant figures? [ENDORSED]

Posted: **Mon May 07, 2018 3:31 pm**

by **Chem_Mod**

n=1 and n=3 are values whose sig figs we DO NOT take into account because we know the EXACT value of these.