Newton’s Rings

I’ve been trying to show my AH pupils all of the experimental work for Unit 3 during this week, as it’s the last week of the course before their NAB next week.

Having gone over much of the theory before Easter and encouraging them to cover the theory on Scholar, I set up a few of the interference experiments – Young’s Slits with microwaves and using a He-Ne laser, which are both nice and obvious and relatively reliable (for physics demos). We took a few measurements and used them to find the wavelength for the microwaves and the slit separation, d, for the laser experiment.

We also used the travelling microscope to measure the slit separation, using a flexi-cam and projector to show both the view down the scope and the readings on the Vernier scale.

Optimistically, I decided to try the same set up for Thin Wedge Fringes and Newton’s Rings – demos which are not so nice and not so obvious and, as I’ve found in the past, can be awkward to set up. Worse still, they must be observed through a microscope, ideally a travelling microscope to allow measurements of fringe spacing to be taken.

The thin wedge fringes worked pretty well and we measured the fringe spacing, using it to calculate the thickness of the wedge. And it all worked!

Continuing to ride my luck, I had a go at Newton’s Rings, using our ancient, somewhat chipped Griffin apparatus. After setting it up, I had a look through the eyepiece and, to my very great surprise, saw the brightest, clearest Newton’s Rings fringes I have ever seen.

To my further surprise, it all looked great through the flexicam-projector, so much so that I took a picture and tweeted about what I’d been doing. One reply, from John Burk (@Occam98) asked how I’d set it up.

So, here goes…..

The images below show how the flexicam was connected to the travelling microscope, using a collar to align the camera and eyepiece lenses, and in turn connected, via the S-Video input, to a Sony LCD projector.

It’s a very rare physics lesson where all of the experiments work, let alone first time. Luckily, when I needed to get through a lot of experiments to gather up the loose ends of the unit, that’s exactly what happened. After all the effort of getting all the apparatus together and set up, getting such excellent images for Newtons’ Rings was a great way to finish my lesson, and coincidentally the Advanced Higher course.

All downhill to the exam now…..

Space Topic – Gas Sampling Apparatus

I’m currently planning a new Space topic for S1, as part of my department’s CfE development. I’d like to do something on sustaining life in space, looking at providing space travelers with clean air, clean water, food and communications during various types of missions.

I’ve yet to decide on a format for the unit, but I’m aiming to do a rich task with the pupils planning how to provide for each need on four different types of mission – Earth orbit, Lunar habitation, Interplanetary travel (e.g. Earth – Mars) and Mars habitation.

There’s not a great deal of scope for practical in most Space topics, and this is a great opportunity to do some cross curricular work in science – it ties together some biology, chemistry and physics. I’d like to do some practical to demonstrate some main points – O2 production/CO2 removal by photosynthesis and chemical ‘scrubbing’, hydroponic plant growth, water purification and signal delay.

ALBA interfacing gas sensors can be used to show CO2 and O2 levels in real time for photosynthesis in plants – link.

Using that experiment as a starting point, this is a bit of kit I’m thinking of putting together to demonstrate the CO2 and O2 content of ‘fresh’ air, exhaled air and ‘scrubbed’ air (using LiOH or similar to remove CO2 from exhaled air).

For each sample I think I could do the following -

• Clean air – with the exit valve closed, pump air from the room into the container, inflating the bag, whilst the sensors display the CO2 and O2 levels.

• Exhaled air – with the exit valve closed, use air from balloons inflated by mouth to inflate the bag, whilst the sensors display the CO2 and O2 levels.

• Scrubbed air – with the exit valve closed and some LiOH in the bottom of the bag, use air from balloons inflated by mouth to inflate the bag, whilst the sensors display the CO2 and O2 levels.

I’m expecting there to be some problems with this, but would very much appreciate some constructive criticism from the Physics/Science community. Suggestions regarding safety concerns, possible pitfalls, or just better alternatives would be gratefully received.

Please click on ‘Leave a Reply’ below to add your thoughts.

Thanks in advance.

AMENDMENT 12/01/10 –

On advice of Graham Dane, from St Augustine’s in Edinburgh, who responded to a posting on SPUTNIK (Scottish Physics teachers’ email forum), I’ve had a rethink about the third demo. Rather than have LiOH pellets in the bag to scrub the oxygen, a separate piece of apparatus will be used as a  CO2 scrubber, before the sampling jar.

I’ve got this made already, but can’t test it until we can source a suitable jar to house the sensing part of the experiment, above.

Graham also pointed out that removing the CO2 would affect photosynthesis, so I might well have a fourth demo to take a stab at.

Not without a suitable jar to house it all in though. Off to the local sweetie shop to procure an empty jar or two…..