# Homework Help: Young's double slit experiment help

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1. May 12, 2016

### 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.

2. Relevant 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

3. The attempt at a solution
I think the controlled variables are the slit separation, s, the distance, D, but im really unsure on the others.

2. May 12, 2016

### BvU

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 !

3. May 12, 2016

### supersub

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

4. May 12, 2016

### BvU

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

5. May 12, 2016

### supersub

Yes im 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. Im just unsure what the 3 variables are, independent, dependent, and controlled variables. The other thing im unsure about is how to plot the graph and if anything is necessary to calculate from the graph e.g. gradient.
thanks again

6. May 12, 2016

### BvU

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.

7. May 12, 2016

### supersub

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.

8. May 12, 2016

### BvU

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 $\lambda\over s$.

9. May 12, 2016

### lychette

AS is an exam level....1 below A !! All teachers or those involved in education know this

10. May 12, 2016

### BvU

This is PF. THere are research physicists from all over the world here too. The point wasn't to find out what AS means, but to seduce Supersub to compose a decent post. That'll also help to write a decent lab report !

11. May 12, 2016

### supersub

Right so independent would be D from the equation and dependent variable is fringe spacing (W). You're right I just had to read my words ha. Just a few things needed, by slope do you mean gradient. I think the fringe spacing is on the y axis is that right? Also so would one controlled variable be slit separation, s, and are there any others? Thanks again

Last edited: May 12, 2016
12. May 12, 2016

### lychette

I hoped that expaining what was meant by AS would help you judge the level of any help that you give.
AS and A level are widely recognised as exam levels. Most research physicists have probably obtained at least AS and A level.