# Young's double slit experiment help

supersub
1. The statement, all variables and given/known data
Hi I'm doing this experiment where we need to find the wavelength of our laser light source. I am unsure what the variables IV and DV would be and the controlled variables? Also how will I make the graph? I'm in AS level so please don't make it too solid for me thanks.

## Homework Equations

so we are to use: w=λD/s where w= fringe spacing D is distance from slit to screen and s is the slit seperation
in the form λ=ws/D

## The Attempt at a Solution

I think the controlled variables are the slit separation, s, the distance, D, but I am really unsure on the others.

Homework Helper
Hello sub,

Eager to help, but telepathy isn't my forte. What are you talking about ? IV, DV, AS don't appear anywhere in my dictionary. Read your own post and try to imagine what someone who is eager to help can make out of this !

supersub
Hey sorry i thought it was common to know it because its how i learned it in class. IV= independent variable DV = Dependant Variable
AS 1st year of A levels. Thanks for your help.

Homework Helper
So that's settled. Now all we have to find out is what 'this experiment' is, 'the graph', and so on

supersub
Yes I am familiar with the experiment. I have done a replica practical using a monochromatic light source (a red laser). Its not so much an essay but more of just a write-up/report of what we found. We needed to find the wavelength of the light source using the formula i gave above. We used a range of D, distance from light source to the screen and measured the fringe spacing of each distance. I am just unsure what the 3 variables are, independent, dependent, and controlled variables. The other thing I am unsure about is how to plot the graph and if anything is necessary to calculate from the graph e.g. gradient.
thanks again

Homework Helper
Yes I am familiar with the experiment. I have done a replica
I know that, but I am asking what you actually did, what you measured, etcetera.
I already understand you varied the distance from the slits (two slits?, separation?, width, ?) to the screen.

supersub
I know that, but I am asking what you actually did, what you measured, etcetera.
I already understand you varied the distance from the slits (two slits?, separation?, width, ?) to the screen.
Right. Yes it was a double slit of one piece. the slit separation was 0.25mm, and the D we started at 1metre from the light source and measured the fringes by using a paper as a screen and marking the fringes on the paper then using a small ruler measured around 10 of them added length and divided by 10 to reduce uncertainty. Then moved it 2m away and repeated it until 6metres and recorded a results table of Distance and fringe spacing.

Homework Helper
Good. So, as you can read from your own account, you varied D and measured the fringe distance. A reasonable graph would then be: measured vertical versus varied horizontal. You expect some relationship ( ##w={\lambda\over s} D## ) that should give a straight line with slope ##\lambda\over s##.

lychette
Hello sub,

Eager to help, but telepathy isn't my forte. What are you talking about ? IV, DV, AS don't appear anywhere in my dictionary. Read your own post and try to imagine what someone who is eager to help can make out of this !
AS is an exam level...1 below A ! All teachers or those involved in education know this