The curved shape of the magnifying lens causes light rays to bend and focus on an image. When we look through the lens, we can use it to make writing or some other object appear larger. However, the magnifying lens can also be used to make something smaller. The light from the bulb is bent and focused on the wall when the lens is held far from the lamp and close to the wall. The image is much brighter than the surroundings. This is because all the light falling on the surface of the lens is concentrated into a much smaller area.


When sunlight is concentrated by passing it through a lens, the result can be an intensely bright and not spot of light. Even a small magnifying glass can increase the intensity of the sun enough to set wood and paper on fire. We are using a light bulb rather than sunlight for this experiment because concentrated sunlight Can be very harmful to your eyes. NEVER LOOK AT A CONCENTRATED IMAGE OF THE SUN.


The United States Department of Energy’s National Renewable Energy Laboratory in Colorado uses solar energy to operate a special furnace. This high-temperature solar furnace uses a lens to concentrate sunlight. A heliostat (a device used to track the motion of the sun across the sky) is used so that the image reflected from a mirror is always directed at the same spot. The lens is used to concentrate sunlight from a mirror to an area about the size of a penny. This concentrated sunlight has the energy of 20,000 suns shining in one spot.


In less than half a second, the temperature can be raised to 1,720° C (3,128° F) which is hot enough to melt sand. This high-temperature solar furnace is being used to harden steel and to make ceramic materials that must be heated to extremely high temperatures.


Concentrated sunlight also has been used to purify polluted ground water. The ultraviolet radiation in sunlight can break down organic pollutants into carbon dioxide, water, and harmless chlorine ions. This procedure has been successfully carried out at the Lawrence Livermore Laboratory in California. In the laboratory, up to 100,000 gallons of contaminated water could be treated in one day.
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Materials


  • Lamp with a single incandescent bulb
  • Magnifying lens


 
Download Student Worksheet & Exercises


Procedure


The results of this experiment may be easiest to observe if done at night in a dark room.


Ask an adult to remove the lamp shade from a lamp that uses a single incandescent bulb. An incandescent bulb is the type that gets quite hot when used. Turn on the lamp. Turn off all the other lights in the room.


Stand about two feet from the wall that is the greatest distance from the lamp. There should be nothing between you and the lamp bulb. Place the magnifying glass on the wall so that the lens is flat against the wall. Now, slowly move the lens away from the wall and toward the light. Keep the lens parallel to the surface of the wall. As you move the lens outward, watch the wall.


 


Observations


Does an image of the lamp appear on the wall? How bright is this image? How big is this image?


Discussion


You should see an upside down image of the light bulb appear as you move the magnifying lens away from the wall. The image should be much brighter than the area around it and much smaller than the size of the real bulb. The image may be only about the size of your fingernail or smaller.


Other Things to Try


Trace the exact size and shape of the magnifying lens on a piece of paper. Cut out this piece of paper and tape in on the wall. Focus the image of the lamp on this piece of paper and copy the bulb image on the paper. Compare the size of the bulb image to the size of the piece of paper. How much bigger is the lens than the focused image of the bulb? Use this ratio of sizes to estimate the increase in the brightness of the image.


Can you explain why the image of the bulb is upside down when it is projected on the wall? See if you can find information about optics in a book or encyclopedia that could help you explain this reversal of the image.


Repeat this experiment using two magnifying lenses. Observe the effect of moving the positions of the two lenses relative to each other and the wall.


Exercises Answer the questions below:


  1. Name three uses for solar energy:
  2. What type of heat energy is transmitted by the sun?
    1. Conduction
    2. Convection
    3. Plasma
    4. Radiation
  3. Circle the following phenomena influenced by the sun:
    1. Pressure
    2. Climate
    3. Weather
    4. Wind

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Comments

3 Responses to “Can Solar Energy Be Concentrated?”

  1. No, any kind of magnifying glass should work.

  2. do you need a certain kind of magnifying glass?

  3. heidi_hancock says:

    cool!