# How to get the value of Rydberg's constant (R) and n_2?

Based from the formula

1/λ = R ( 1/ (n_2)^2 - 1/(n_1)^2 )

If I get the graph of 1/λ (y-axis) vs. 1/(n_1)^2 (x-axis), how do I get the value of R based from the slope and n_2 based from the y-intercept? Thank you :D

### 1 Answer

- Steve4PhysicsLv 77 years agoFavorite Answer
1/λ = R (1/n₂² - 1/n₁²)

1/λ = R/n₂² - R(1//n₁²) (equation 1)

You need to be sure which quantities are variables and which are constants.

1/λ and 1/n₁² are variable quantities

R and 1/n₂² are constants.

Compare equation 1 to y = c + mx and you can see:

- the variable y is equivalent to 1/λ

- the variable x is equivalent to 1/n₁²

- the constant m is equivalent to -R

- the constant c is equivalent to R/n₂²

FInd the gradient (which should be negative); since gradient = -R, R = - gradient.

Find the 1/λ intercept and then use:

Intercept = R/n₂²

n₂ = √(R/intercept)

n₂ should work out to be (close to) an integer.

If you are using SI units, make sure λ is in metres, so 1/λ has units of m⁻¹ by the way.

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