# QM light experiements at home.

1. Jul 30, 2004

### Glenn

Hi,
Reading about physics is a pastime of mine. I have read about many of the famous experiemts such as Young's double slit experiment and such.

I would like to do some of these experiements at home to start teaching my kids about QM and light.

What types of QM light experiments are within reach for the serious home experimenter? Are there any books or references that are tailored to this type of work?

I am an engineer by day, spend my after hours building full size experimental aircraft, telescopes, etc... so complex or precise construction won't scare me away, nor will a having to purchase some moderately priced components if need be.

Any thoughts or recommendations?

Thanks,
Glenn

2. Jul 30, 2004

there is an easy experiment with single slit diffraction. All you need is a 5 dollar laser, you can purchace them nowadays in convenence stores. What you do is take a human hair, strap it vertically between two holders and let there be vertical portion hanging out in mid air. Now aim your laser at the hair, and observe the effect about 5m away. It would act as a single slit and it should have a single slit diffraction pattern. You can calculate the width of the hair by measuring out the spacing of the fringes of light 5 m away. Use equations like dsin(theta) = m(lamda), where d is the width of the slit, or hair in this case. m is the fringe number as an integer, starting from the centre fringe as 0. Lamda is the wavelength of light. You can also use dx/L = m(lamda), where x is the fringe spacing, and L is the distance from the screen to the hair.

You can also do and experiment with soap bubbles. When you watch a soap bubble, you see different colours at different heights of it. This is double inversion, and it teaches about thickness of the bubble and the wavelenght of light.

You can also do a diffraction grating by aiming your lased at a cd. You will see a grating appear on your ceeling if you aim the laser at a 45 degree angle. Using the equations I stated above, you can find out lots of neat stuff about CD's and light.

3. Jul 30, 2004

### HallsofIvy

Staff Emeritus
My God! Now people refer casually to "5 dollar lasers" that you can buy in convenience stores! Am I the only one so old that I can remember when lasers cost a hundred thousand dollars and required a whole room to themselves?

(Now that I think of it, I also remember when computers required a whole room to themselves- and had 16 K memory!)

4. Jul 30, 2004

### ZapperZ

Staff Emeritus
Oh, phew! I thought I was the only one who still remember computer punch cards! :)

Zz.

5. Jul 30, 2004

### jcsd

You don't need a laser in order to perform the Yojung's double slit experiment, infact all you need is a light bulb, some 'blinds' and a metal sheet with suitably sized slits (when I was school we had loads of these kits consisting of a normal light bulb in a wooden frame with suitable places for blinds and slits to be slotted in).

6. Jul 30, 2004

### jcsd

Of course though ther double slit experiment only really demsontsrtes the classical wave model of light and doesn't in itself demonstrate the need for quantum physics.

7. Jul 30, 2004

### vanesch

Staff Emeritus
Indeed, I think that if you want to demonstrate quantum properties, that you need one, or a few, photomultiplier tubes, with associated electronics, and a oscilloscope and/or an acquisition system on a PC. This can quickly become expensive (although maybe not for someone who builds airplanes in his spare time

cheers,
Patrick.

8. Jul 30, 2004

### jcsd

It's a question that's been asked svereal time before and I've always been a little dubious of whether some of the cut-price experiments that have been described will unambigously demonstrate what they are meant to demonstarte.

That said I guess that an experiment to illustarte the photoelectric effect and thus show the quantum nature of light wouldn't be too hard to perform.

9. Aug 1, 2004

### valhalla_127

I have a way. Take a card from a deck or an index card or something, get a flashlight, and poke two holes in it that is smaller than the circumfrence of the flashlight head, and at night put the card up to the light with the two holes inside, and aim it at a ceiling or wall. You will see two lights, but in the middle will be the brightest spot of all, with two spirals connected. It is very beautiful, but it is too complicated to write how it does this here.