$100 close up

Turn Your Mobile Phone into a Mobile Microscope [W/Video]

Can the new Cell Phone Magnifier unlock why Mint Mentos are better than Fruit Mentos for making soda explode? Check out this cheap option for those times when high-powered microscopes aren’t necessary.

Arbor Scientific has a marvelous Cell Phone Magnifier that can easily be attached to a cell phone camera and turn it into a microscope.

You can use it anywhere you want, any time you want; for example you can investigate something on your nature walks that would be interesting microscopically such as an insect or plant. But I have found a lot of use for it in my lab when I view or photograph something microscopic. In this article I will provide some examples of interesting objects to view and discuss some details of the physics of the lens.

Examples of Interesting Objects
For starters, here is the surface of an ordinary piece of printer paper. This shows quite easily that it is not smooth at all. This is important for explaining why paper does not reflect light the same way a mirror does (diffuse vs. specular reflection).
paper
mentos-1 Here are up-close pictures of Mentos candies.

Can the microscope unlock their secret powers of soda exploding?

mint

The Mint Mentos display a pitted surface.

fruit

 

The Fruit Mentos have a glaze that inhibits nucleation sites.

You can clearly see the dimpled “nucleation sites” that are the catalysts for releasing the bubbles from soda. The Fruit Mentos is more glazed over and does not work as well as the Mint Mentos.

The new $100 Bill is an excellent candidate for this tool.  Many of its security features are only appreciably if you have a microscope.  For example, the tiny security writing along the length of the feather, or the security threads that are thrown in to curb counterfeiting.  Also, note that you can clearly see the color changing glitter is lain in different directions on each side.  Shine a flashlight at the bill for best results.  Don’t miss the raised ink on the front of the bill, you can feel it with your finger, but only with a microscope can you recognize the very specific patterns that in the relief.

100

Illumination from the side helps the features of the new $100 Bill to stand out.

 100close

The color change glitter effect comes from having different colors on each side. 

100rased

Raised ink and holograms are among the new features.  Note the pattern is the Liberty Bell. 

onehundredusa

A security fiber and the micro printing are best viewed through a microscope lens. 

One of my favorite experiments is to hold it up to a computer screen and see the different pixels that are making the colors.  The lens offers an excellent opportunity to study how the primary colors of light are combined to generate new colors.  When looking at pixels, I recommend the Google.com logo.

 

google

This summarizes what you will take away from viewing the Google logo microscopically. 

You will be using a computer screen anyway and it is such a familiar sight that students find this investigation highly amusing.  Also look at the black cursor with a white background, to learn how white light is made.  While you are at google.com you might as well do an image search for specific colors, like pink, or brown and find out how they are made by mixing RGB.

 

Speaking of mixing colors, take a close look at an image in a text book and see that these pictures are not made from RGB, but rather the primary colors of ink, CYMK.  Cyan, yellow, magenta, and black are unequally mixed to form the color desired.  For example, cyan and yellow makes green.  That they are not red, yellow, and blue, is sometimes a surprise.  Note also how messy individual letters look close up.

CMYK image

A CYMK print image of a red car, green bushes, and a blue sky. 

Pretty much any grain or crystal will look very interesting microscopically.  Take a closer look at your rock collection or – even easier – just take some condiment packets from your local restaurant.

salt, sugar, pepper, and sweet'n low

Some good things to image that you can probably get for free.

salt close

To hold the world in a grain of sand.

Pepper close

Of course insects offer a wonderful venue for this lens.  Because the camera is mobile, you now can look at and photograph living insects more easily.  Nonetheless, I still enjoyed looking at my insect collection with the camera.

wasp close up

A wasp from my students’ collections.

fly close up

A flesh fly from the same collection. 

The Physics of the Lens

Using your cell phone as a microscope has advantages beyond just the fact that it helps you make and share videos and pictures.  One of the best things is that your camera has an autofocus, which makes it easier to get the image.  Also, since the lens is making a virtual image, you do not have to move the object oppositely to the direction you want the image to move (this is a major annoyance when using conventional microscopes).

The lens has a focal length of about 1cm.  I found this by projecting a real image of my ceiling lights and by assuming that since the object distance is so much greater than the image distance, that the focal length is the same as the image distance ( 1/f  = 1/do +  1/di ).

 

lens

When the image distance is much smaller than the object distance, the focal length is very nearly the same as the image distance. 

Our website (Arborsci.com) says that the magnifying power is 15 times.  I found this to be true.  I first took a picture of an ordinary meter stick without the lens and found that my iPhone’s lens had a magnification of 2.  Then I took a picture of a ruler with and without the lens, and compared those.  Here I found the increase to be a little more than 7 times.  (Images must be in focus.)  The product of 2 and 7.5 is 15 which is very the same as the advertised value.  I am using the definition that magnification is the ratio of the image height to the object height.  Since our images are not upside down we have a +15.

 

Since the lens needs to be sticky to stick to the cellphone, it also is sticky to dust.  This is easily washed off however, either by a little water or more conveniently and effectively saliva.  The instructions recommend water with a little soap, but water alone is usually sufficient.

 

Conclusion

I am surprised at how much I have come to like having this little attachment.  I have been using it whenever I need to show my students things that are better appreciated through a microscope.

 

With the advent of every student having a camera in their pocket, it would certainly not be an unjustifiable purchase to buy a class set of these to increase engagement when learning about lenses or any subject that uses microscopes.  If you are interested, you should definitely buy one to try it out; you’ll be glad you did.

 


James Lincoln
Tarbut V’ Torah High School
Irvine, CA, USA

James Lincoln teaches Physics in Southern California and has won several science video contests and worked on various projects in the past few years.  James has consulted on TV’s “The Big Bang Theory” and WebTV’s “This vs. That”  and  the UCLA Physics Video Project.

Contact: [email protected]


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Kinetic energy into thermal energy [W/Video]

Watch how silly putty and simple steel spheres can be used to demonstrate the conversion of kinetic energy into thermal energy! (And you thought Silly Putty was for copying comics from the newspaper!)

One of the most important concepts in physics is the principle of energy conservation, especially the idea that energy can change forms and be transferred from one object to another. An important application of this idea is that kinetic energy can be transferred to heat, which is just another form of energy. One way to demonstrate this idea is to have students simply rub their hands together, showing that friction transfers energy into heat. However, it may be less obvious to students that impacts also generate heat, since the role of friction may not be as clear when the objects are not actively rubbing together. One easy way to demonstrate this is with a set of Colliding Steel Spheres. When I use this demo in class I ask for a “brave student volunteer.” I have the student volunteer hold a sheet of paper vertically and then I dramatically smash the spheres together with the paper in between. A small hole results and I have the student examine the hole, in particular noticing that there is a smell of burning paper. This clearly shows the class that the kinetic energy of the moving spheres is changed into heat energy when the spheres collide. I then typically make several more collisions to drive home the point, and sometimes allow students to try it for themselves.

swiss_cheese_paper_600

Another dramatic and visual way to demonstrate this concept uses silly putty, a hammer, and a temperature probe connected to computer data acquisition system. Simply embed the temperature probe inside the silly putty, start the data acquisition, let the temperature come to equilibrium and then smash the hammer down on the silly putty. You should then see a rise in temperature recorded on the screen, again showing how kinetic energy is transferred into heat energy, resulting in a rise in temperature of the silly putty.

fire syringe
Another great way to show energy conservation, and connect to thermodynamics concepts, is the Fire Syringe. This is basically a piston that you can use to rapidly compress a column of air with a bit of cotton ball; the rapid compression heats the air and ignites the cotton ball. This again is an illustration of converting kinetic energy into heat; you can also present this in the context of the idea gas law, where the compression increases the temperature. A couple of things to watch out for when using this device: the seal needs to be good, so the o-rings should be lightly lubricated and when you compress the piston it should bounce back rapidly; use a small bit of cotton ball and pull it apart so there is a lot of surface area to heat. You need to give the piston a quick compression, and it helps if the cotton fibers are near, but not sitting on, the bottom of the column.

These demos are visual and, for many students, surprising, and can really drive home the idea that energy can change forms and particularly that kinetic energy can be changed into heat energy.

Brian Thomas is an Associate Professor of Physics & Astronomy at Washburn University’s College of Arts & Sciences His Career Accomplishments include but are not limited to: Principle Investigator on a $500,000 research project funded by NASA’s Astrobiology program, in collaboration with the Smithsonian Environmental Research Center, author or co-author on approximately 20 peer-reviewed articles. Invited speaker for several international conferences. His work has been featured in news articles, as well as in several television documentaries.
washburn.edu/our-faculty/brian-thomas


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