Friday, July 07, 2017

Lab equipment older than me

While continuing to clean my prep room (no end in sight!) I found more old Macalaster Scientific Corporation boxes similar to the radiacmeter and dosimeter I found a few weeks ago. I found four different pieces of equipment, it has been interesting to research them, find out what they were used for, and try to determine if they can still be used. The company seems to have stopped production in the 1960s, although upon searching for their equipment I see many familiar things. My dynamics carts from my Crash Cushions project are apparently made by Macalaster and potentially 50 years old. Perhaps new dynamics carts will be on my shopping list this year ...

Mass of an Electron Apparatus
This uses a "Magic Eye Tube" with a circular display that was used to tune radios in the 1930s. My equipment, shown below left, had to be used with an air core solenoid, shown below right. From what I can tell these can still be purchased for about $100 each (solenoid not included) and used as demo equipment.

The instructions puzzled me a bit as they referred only to assembly so I turned to the instructions of a similar modern version.

This video shows the magic eye tube changing as a radio is tuned in and out:
It took me awhile to realize that when not used with a radio, the magic eye would produce a straight edged fan shaped wedge that would be unchanged (bottom right).  That is, unless a magnetic field is brought near it to bend the electrons and the fan shape on the display (bottom left).  That is where the air solenoid comes in, constructed to be about twice the height as the fluorescent screen on top of the magic eye tube so that it sits at the center of the solenoid. The magnetic field around the solenoid when current is running through it effects the electrons on the fluorescent screen.

The explanation describes an experiment to determine the mass of an electron approximating the curvature of the "fan" shape using something else round. You seem to need to know multiple voltages, the current and turns in the solenoid (to determine's magnetic field strength) and the curvature of the bend. The instructions end with "Refer to physics text books for the formulae relating to the calculations for the strength of the magnetic field and the velocity of the electrons. From this information you can calculate the approximate mass of a single electron." Not quite spelling it out for us, is it?

I found this image and equations on Hyperphysics that I think match up with this experiment.

I'm not 100% sure that this is the correct equation for finding the mass of an electron with a magic eye tube but it looks promising. The radius of the curve of the electron deflection due to the solenoid's magnetic field would be found by matching it to a circular object. Since it would be hard to accurately measure the radius of only part of a curve, the instructions suggest that if you find something else that has the same curvature but is a complete circle it will be easier to measure the radius. The magnetic field strength of the solenoid could be found by knowing the current through it and the number of coils. The voltage should be measured from the circuit, charge on one electron is known and that should reveal the mass of one electron.  

Potential Difference Kit
From the brief assembly instructions I think (1) I'm missing an insulating handle and (2) it is acting like an electrophorus. (Here is an Electrophrus Engineering activity by the way.) That is my guess at least, maybe someone else has a better idea of what this #unknownequipment is used for.

Tangent Galvonometer Kit
The dismantled frame (left) can be assembled (right) to make a base to hold a compass and a loop of wire. A compass (not found in the box) would be placed where the spool of wire is placed on the right. A square loop of wire is made around the four nails (two top, two bottom) that surround the compass resting on the base. This modern version shows the same set-up. There are fancier equivalents of this kit with secured circles of wire around mounted compasses. I've made similar set-ups for students with cardboard in class (start video about 30 seconds in).
I was surprised to read "This can also be used to determine the magnitude and direction of the horizontal component of the Earth's magnetic field." in the description. I found this explanation of the experiment but I'm not sure if this particular rudimentary kit would be successful. This kit is quite large, about a foot tall, and has sharp aluminum edges. This particular one has been defaced with an engraved swear word as well. While it could be useful, I can probably make some that are a bit easier to worth with.

Cathode Ray Tube
I figured it lit up when I saw it but Dan was able to tell me that this piece of #unknownequipment was a Cathode Ray Tube. This Lab Guy post shows how it could be hooked up and made to work like a small TV. That is way above my current summer level of work load though. Dan also said he powers one with a handheld Tesla Coil so until I procure one of those this may not be useful.

While I might be able to get some of these to work, some would require purchase of additional materials. One could find such vintage pieces on eBay but it begs the question, do you want to? They still hold some educational value, if their original purposes are known, but it may not be worth trying to get them to work. For the time being they will remain on a shelf with other vintage pieces I can't bear to part with.


Dean Baird said...

My recollection is not always spot on, but I believe that old Macalister apparatus was designed for and aligned with the PSSC Physics lab manual. The apparatus always struck me as very specialized and each item seemed to be used on only one lab activity. Not my cuppa, but it worked wonderfully for many.

Back in the post-Sputnik years of the '60s and '70s, PSSC Physics and Harvard's Project Physics were the big, dominant curriculum projects. Eventually their stars faded, but in the '60s and '70s, they ruled the roost of American high school physics. If you can find an old PSSC lab manual, I'm pretty sure you'll see labs written for those pieces.

Dean Baird said...

I use the air core solenoids as ... wire coils for induction applications. But also as bases for the embroidery hoop inertia activity.

Hoop Dreams Success (300 fps)

Jeff Sensabaugh said...

My lab has much of the same equipment! We use the air coil solenoids for lots of magnetism demos. It's fun to use them to 'vacuum' up iron filings. Two, side by side, make an impromptu transformer. Just hook one coil up to a sine wave generator and the other to a galvanometer. If you drop a the handles of a pair of pliers into the centers of the coils you get a much stronger signal.

We also have little PSSC see-saws that go into the mouth of the coils to make a current balance. There are little clips that you attach to the side of the coil; the see-saw balances on points resting on the clips, with one end sticking out and one end enclosed in the coil. The enclosed end has a wire that traces from the points to the enclosed end of the balance. By adjusting the current you can get the beam to balance horizontally. It's simpler than it sounds; I'll try to post some pictures next week.

I decided to try the tangent galvanometer lab with my AP students this year, just to see if it works. It was one of my most accurate labs, with many groups matching the NOAA estimated field by 5% or less. ( The hardest part was finding the field equation of a square coil!

Heather Stirewalt said...

Thanks, I have been scouring the internet for information on these old Macalaster pieces of equipment! I am trying to figure out the current balance kits for a decent AP Physics 2 lab, It would be nice to not have to pay $300 each for PASCO current balances. Are you able to get decent data from this setup Jeff? I also have the mass of electron apparatus, tangent galvanometer and others. Thanks for the tip on the PSSC Lab Manual... I think I actually have a few of those!

Jeff Sensabaugh said...

The equipment for the current balance has seen better days. If I use them, it's just to have kids test their right hand rules against real situations. I don't have them do anything quantitative with them. I only have some of the documentation that came with the equipment and the balances are not in great shape, so measurements are not going to work well. I might try doing some repairs. Are they really $300? Maybe I can build something in the school's shop...

The Tangent Galvanometer kits, though, worked like a charm.

I recognized the q/m tube from when I did the lab 30 years ago. We have a set but I've never done it with my students.

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