Opening up the world of light

Light is one of those things that we usually tend to take for granted and remember the utility of especially when stubbing a toe or hitting a thigh on the handrail of the stairs in the dark when the distance is calculated wrongly as the bathroom door was open wider than usual. It is also one of the physical phenomena which interest me the most now as I am reading and understanding more about how it relates to electricity and magnetism. Light is electromagnetic radiation and visible light is just a small part of the whole spectrum of light. However, this aspect of it is a bit too advanced for my four-year-old. So, today, we started to study the light we could see. We did not do them in quite as organised a manner as I demonstrate below, but I decided to tidy up the process for you.

1. Playing light-agents

First, as a way of introducing the topic, it is possible to play light agents. These agents go around the house and see all the things that create light. There is a surprising amount of them in this time of LED-lights in all the electronic gizmos around the house. Don’t forget to look out the window.

You can also google the plethora of light experiments found on Youtube. I showed my daughter THIS ONE to get her into the mood for experimentation.

2. Study light and shadows

For this you need a) flashlight, b) smartphone OR c) sunny day + window (cover up a window and prick a hole in the covering) and a dark room. I used my smartphone, which has a flashlight as daughter had been playing with our flashlights and I had absolutely no idea where they were.

Study with the child how the light travels in the room. What happens if something comes in the way of the light? It creates a shadow, because light travels in a straight line. A  shadow happens, when something comes to reflect, absorb or refract (in Finnish: taittaa valoa) the light waves. This bit was a great deal of fun with my daughter as I made shadow-animals and they chased her shadow-animals around. The shadows prove the light travels in a straight line unless something refracts, absorbs or reflects it.

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Light and shadow games with daughter

3. Study the spectrum

For this you need a prism, or also a CD works, and a darkened room

Next we studied the phenomenon named white light. We have a pyramid made of glass and I used that. I put it next to the light source and it refracted the light in a way that separated the different wavelengths of light and showed a myriad of beautiful colors of the spectrum of visible light. I explained that all these colours are in white light, that they are different wavelengths of colour and as the prism refracts the light, each wavelength is refracted at a slightly different angle.

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White light contains all the colors of the rainbow. Here light from my phone is refracted into different wavelengths with a prism.

4. Reflection (in Finnish: heijastuminen)

For this you need a light source and a mirror and a darkened room.

Then we proceeded to study, how light is reflected. I first used a laser pointer to show how it is reflected from the mirror, but that was a bit of a mistake as my daughter wanted to try it too. I did not want her to, because I had a vivid image of the laser light flashing in her eyes, my eyes or the eyes of my younger daughter. So I took the baby out of the room and talked my older daughter (4 years old) into accepting the light from the smartphone instead. We reflected the light of the mirror onto the floor, walls and ceiling.

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Reflecting light with a mirror to a cup, with water and some of daughters’ little treasures. Her own experiment design :).

5. Absorption (in Finnish: imeytyminen)

For this you need a light source, a hand, different colour papers, black cardboard and another cardboard of a lighter colour (same width). A dark room helps, but is not absolutely necessary. A laser pointer is optional.

Then we studied, what light does when passed through the hand. Most of the light is absorbed, but red light is passed through (humans are mostly red inside). So I told her this. We then tried moved onto the laser pointer and I turned it on and put the yellow cardboard (it was what we had on hand) and showed that some light came through. Then I put the black cardboard in its place and nothing came through. I told my daughter that the cardboard looked black for exactly this reason. It absorbs all the light, all its wavelengths. Then I asked her to fetch different coloured papers from her room to experiment on. She came back with pink, blue, white and green. We put each of these in front of the flashlight. Pink paper coloured her hand and the table pink, green coloured it green, blue coloured it blue and white did not colour it at all. I explained that the coloured papers looked that specific colours just because that is the wavelength of light they reflects as it absorbs the others. White lets everything through so it did not colour anything differently.

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Experiments in absorption. Upper level: How white colour changes colour, when passing a coloured paper and hand, as other wavelengths are absorbed. Below: laser light is completely absorbed by black cardboard while passing through similar (besides colour) yellow one.

6. Refraction (in Finnish: taittuminen)

Lastly we studied refraction. For this you need a glass/bottle, water, a straw or pen, a coin, cup you cannot see through, and a paper with an arrow. Actually, you may not need all of them as they demonstrate refraction in different ways.

First I poured some water into the glass and put the straw in. I then asked whether the straw still looked straight or whether it bent at some point. She told me that it did not look straight. I explained that this is due to refraction, that light traveled differently in water than in air and that is why it looked like the straw was bent.

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Straw experiment. The straw looks to bend due to refraction.

We then put a coin on the bottom of a cup in a way that we did not see it. I then poured water very gently so as not to move the coin and, like magic, the coin appeared. Lastly I drank the water from the glass, drew an arrow on a piece of paper and asked which way the arrow was pointing (left). I then placed it behind the glass. I asked daughter which way the arrow was pointing now. She showed me (left still). I then poured water in the glass and asked again. This way the arrow pointed right, although the shape of the glass made it less obvious. A bottle probably works better. Again I told her that the water affects the light and it moves differently and is refracted at the surface of the water.

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Experiment in refraction. First upper left: An arrow drawn on paper. Bottom left: a glass in front of the arrow. Right: water in glass -> the arrow changes direction because of refraction of light

To finish up

We made a list of all the things we now know about light:

  • it travels in straight lines unless something refracts it
  • shadows are formed as something stops (absorbs or reflects) the lightwaves. If the light could travel in something other than a straight line, shadows could not exist
  • White light is composed of all the colours of the spectrum
  • Light is reflected for instance by a mirror, which does not absorb the light
  • Light is absorbed by different coloured items and all the white light (or red light from a laser pointer) is absorbed by black, which is why it is black. If the item is coloured in something other than black (absorbs everything) or white (absorbs nothing) then it will let the wavelengths through (or reflects them) that match the colour it is, which is why it is of that colour.
  • Light is refracted if it travels through liquids or solids.

Then, just as a repetition, we explained all these to my husband. Daughter explained all she could and I helped a little. As a follow-up I do need to try these again with her and talk about these as we run across the same phenomena or related ones. This way this information is something her little growing brain realises is something worth keeping and not just forgotten (see spaced repetition).

If you try this at home and your child asks questions (mine doesn’t, really), please let me know in the comment section so I can further develop these instructions. Also, please remember like and share if you find this useful.

 

 

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