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February 14, 2010

Science: Burning Paper With a Magnifying Glass

Seeing it's a beautiful sunny day today I took advantage of it and went ahead and did one of our science activities for this week. We are using Behold and See 3 for science. Our chapter is about the sun, moon and the stars. Our activities have to do with the sun, moon, and stars. On page 73 it actually suggest this activity to learn about how "hot the sun is". This is something that NEEDS to be done with parental supervision.

I have a 4x Magnifying Glass. We took it outside and focused the sun's rays onto a piece of paper to make it burn. Very much like in this video below.
We at first had a hard time with this we couldn't get things to burn. I just had some plan white computer/printer paper. I thought perhaps that we were moving around to much and not keeping still. So I brought the paper in and put a small x on it with a pencil. Took it outside focus the sun rays and within seconds the paper was smoking and we had a hole burned into it.

We then tried on a different spot and could not get it to burn. So we came back in and wrote some more xs and other things on the paper with the pencil. Everywhere that we wrote, with pencil, went up in smoke and had a hole in it within seconds. We know that lead has something to do with that but we are not sure what it is exactly.  We don't understand why we couldn't get it to burn without the lead.

Perhaps it's because it's the middle of winter here? The weather is in the 20's and there is snow on the ground.  Perhaps it's because we are using a 4x magnifying glass? It might not really be strong enough to burn the paper? Perhaps these factors are making it difficult for the paper itself to burn. However it burns within seconds anywhere there is lead. Perhaps the leads burning point is lower?? Or the lead is acting as an accelerator? Don't really know for sure, but he had fun burning the paper.

Later this week we will actually have a discussion on this and will be able to say remember Sunday on how we did that. If it's a sunny day when I plan on having the actual discussion we will go out and burn more paper. I just wanted to do it today in case it end up being a cloudy day later this week.

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  1. I suppose it's possible that the color of the pencil marks helped the spots heat up, but it's not because it's lead. The lead in pencils is actually graphite. Did you try using papers that were different colors to see if they burned quicker than the white paper? It would probably be neat to see if darker colored papers burned faster than lighter colors.

  2. DUH! Graphite.... LOL (I should have or think I knew that at one time). So much for this homeschooling teacher knowing her stuff! LOL Different color paper now that's something we can try later this week. I'm sure I'll make it point to find time to do it again this week. :) Or next if the weather doesn't work with us LOL.

    It would be neat to see if color effects the rate that it burns. I just mention that to the kids. I've got blue, green, and purple paper on hand and I'm sure I will find a few more colors sometime this week try out.

    Thanks Karen!


  3. Using just colored markers to color different patches on the white paper will allow you to see that things that are white are harder to burn.

    White things tend to bounce back all the light that's shined onto it, so no light OR energy absorption; therefor no color and a very weak heat source. but when you color the paper it absorbs that specific wavelength of light which is enough to allow the paper to burn

    When I did this i was then able to continue over to the white parts of the paper... i think this is because im not really burning white paper but the scorched marcks just in front of the beam.

  4. Buz- Thanks for visiting and for your comment! That makes total sense! I'm thankful that you shared your insight with us!

  5. White paper doesn't burn with a magnifying glass because it reflects the heat. When you put the dark pencil markings on the paper it attracted the heat and made it burn.

  6. buz: but when you color the paper it absorbs that specific wavelength of light

    A little correction - The colour that the paper is, is actually the wavelength that is reflected from the paper, i.e. it's all the other wavelengths that are absorbed.

    So, a completely white paper reflects all the wavelengths and absorbs none, thus there's no heat, while completely black paper reflects no wavelengths and absorbs all, converting it to heat.

    A better lens in summer would make you able to burn white paper as well.
    It takes a little time to get it going, but as soon as the paper starts getting brown because of the heat, it's less than a second before it burns away.
    Newspaper is good to use - cheap, and lots of black lettering.


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