# Homework Help: Error equation for the balmer series

1. Mar 12, 2013

### wahaj

1. The problem statement, all variables and given/known data
I have to find the error in λ determined by the Bohr model/Balmer series. I am a bit confused with this so I'd like someone to double check my work. I don't know the exact name of this method but basically all you do is take the differential of all the values which have an error to find the error of the determined value.

2. Relevant equations

$$\frac{1}{\lambda} = R (\frac{1}{n^2_f} - \frac{1}{n^2_i} )$$
nf and ni are discreet values so they have no error in them
R is the Rydberg constant and has an error of +-1 in the last digit so
R = (1.097 +- 1 ) * 107 m-1

3. The attempt at a solution
$$\frac{1}{\lambda} = R (\frac{1}{n^2_f} - \frac{1}{n^2_i} )$$
$$\frac{\delta \lambda}{\lambda^2} = \delta R (\frac{1}{n^2_f} - \frac{1}{n^2_i} )$$
$$\delta \lambda = \lambda^2 (\frac{1}{n^2_f} - \frac{1}{n^2_i} ) \delta R$$
The reason I am confused with this is that I am trying to find the error in λ but λ shows up on the right hand side of my error equation. Also did I get the error in R in the right decimal place?

2. Mar 12, 2013

### Simon Bridge

First: replace everything in brackets with 1/K and solve for lambda.
Now find the error on lambda - should clear up your confusion.

3. Mar 12, 2013

### wahaj

that works thanks

4. Mar 15, 2013

### dab353

So is the equation supposed to look like as follows: δλ=λ2(1/K)δR??? Im so confused.

5. Mar 16, 2013

### Simon Bridge

@dab353: welcome to PF;
Take it step-by-step.