Praxis: Glass, water, air and the blending of light

By Patty Rooks on October 26, 2019.

praxis@praxismh.ca@PraxisMedHat

Our 28th annual Family Science Olympics have finally arrived! Please do not forget to stop in to Medicine Hat College from 10 a.m-3 p.m. today to enjoy some fun hands on science experiments for all ages. am excited to see what the Education Students have put together for all of us to do. They are an amazing group of students so I have no doubt this is going to be a fun filled day of learning for all. Even after all these years, this day is so exciting for me, as I just love seeing the awe on the faces of all the scientists that come out to have fun. I thought I would share a little “blast from the past” and do an experiment we did a number of years ago at the Family Science Olympics. I look forward to seeing you soon!

*Remember to ask an adult before doing this experiment.

Materials

– one tall clear glass drinking glass

– water

– index cards

– black Sharpie marker

– sturdy work surface

-science helper

Procedure

1. Find a good sturdy work surface to do the experiment on.

2. Take a blank index card and draw a large horizontal arrow in the middle of the card with the marker.

3. Have your science helper place the note card behind the glass of and slowly move the index card back and forth.

4. What’s happening?

5. Bend/sit down and look through the glass from the front and observe the arrow.

6. Does anything happen to the direction of the arrow?

7. Fill the glass three quarters full of water.

8. Place the index card behind the glass of water and slowly move the index card back and forth.

9. Bend/sit down and observe the arrow through the glass from the front.

10. What appears to happen to it?

11. Try this with different shapes.

12. What happens?

What is going on?

How does the glass of water do that? No, you aren’t going crazy and you haven’t found yourself with Alice in Wonderland staring at arrows pointing in opposite directions. In fact, you have just demonstrated a physics concept called refraction, the bending of light.

When the arrow is moved to a particular distance behind the glass, it looks like it has reversed itself. Did you know that when light passes from one material to another, it can bend or refract?

In the experiment that you just completed, the light had quite a journey; it traveled from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Anytime that light passes from one medium, or material, into another, it refracts. Just because light bends when it travels through different materials, doesn’t explain why the arrow reverses itself.

To explain this, you must think about the glass of water as if it is a magnifying glass. When light goes through a magnifying glass the light bends toward the centre. Where the light all comes together is called the focal point, but beyond the focal point the image appears to reverse because the light rays that were bent pass each other and the light that was on the right side is now on the left and the left on the right, which makes the arrow appear to be reversed.

Party Rooks, Senior Scientific Consultant PRAXIS, “Connecting Science to The Community”. Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. NOTE our NEW address: #12 826 11 Street S. E., Medicine Hat, Alberta, T1A 1T7 Phone: 403-527-5365, email: praxis@praxismh.ca.

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