Generation Next: Fun with Light!

Generation Next: Fun with Light!

November - December 2009

While conducting our Ozone module with 9th standard students at Dream School Foundation’s (DSF) education and development centres, we recognized a lot of parallels between this unit and their science chapter on Light. Sackhumvit Trust and our volunteers organized a series of experiments to facilitate students in understanding this topic as part of our Generation Next program.

One of the first things we realized was that the 9th standard science textbook immediately jumps into an analysis of how light interacts with lenses, without explaining what light is. When asked for their ideas, students shouted out words such as “energy”, “the sun”, etc. While correct, our first objective was to deepen student’s understanding of light and its importance to our daily lives. This was made possible largely due to a unique presentation prepared by Professor N. Chandrasekaran on the concept of light and its applications, which served as the foundation for the initial part of this program.

Students examined the wave and particle theory of light, and learned about the discovery of photons. We then reviewed the entire electromagnetic spectrum where students learned about the relationship between wavelength, frequency, and energy, as well as the various uses/roles of the energy the Earth receives from the sun. A useful activity sheet for this topic came from the United Nations Environmental Programme’s (UNEP) High Sky: Ozonaction Education Pack for Secondary Schools. Students had to piece together a puzzle of the entire electromagnetic spectrum based on clues on the use/importance of each type of radiation along with their respective wavelengths and frequencies.

Following this, students focused on a specific section of the electromagnetic spectrum: visible light. Here students learned about the role that light plays in coloring everything we see in the world. Many of them were boggled by the idea that our experience of the world is essentially a matrix, with photons of light registering in our eye to create what we see. Students reviewed the primary colors (red, green, and blue) and how combining these colors will create almost any other color. They found it interesting that the old name for computer monitors (RGB monitors) is based on the fact that they use the primary colors to generate images on the screen.

This was followed by an experiment called “Colors by Addition”, where students used three torch lights (each covered with red, blue, or green filter paper), to create various combinations of colors. Students noticed that when all three torches are superimposed on each other, they create white—hence white is made up of all the colors in the visible spectrum.

After completing “Colors by Addition,” it was only logical that we explore “Colors by Subtraction.” Here students learned how we see colors not by their reflection, but by their absorption! It was explained that this mainly applies to inks, dyed cloth, and other materials that are not a light source, yet give off color. We see these items mainly because of the visible wavelengths that they do not absorb, i.e. we see the radiation that is left over after they have absorbed or subtracted certain radiation.

This concept was illustrated by a simple experiment where students mixed different colors of paint. For example:

•Magenta (a combination of blue and red, with all other colors being absorbed) mixed with

•Yellow (a combination of red and green, with all other colors being absorbed)

creates the color red, because the blue and green wavelengths get absorbed. Students found this concept harder to grasp than “Colors by Addition,” but nonetheless enjoyed predicting what colors they would create from various combination of paints.

As a primer to the textbook discussion on light and lenses, we covered one last concept of light. This is the various ways in which light can interact with an object: transmission, absorption, reflection, scattering, and refraction. As we already covered the concept of reflection and absorption in terms of seeing color, students readily picked up these concepts. To further illustrate the concept of reflection, students built their own kaleidoscopes and periscopes using the reflective properties of mirrors. This activity was a big hit amongst students, with most of them requesting to take their inventions home.

For the remaining processes, we conducted simple experiments to explain what they meant.

• For transmission, students observed a piece of glass and how the can see perfectly through it, hence demonstrating how light passes directly through an object without any change.

• For scattering, we conducted a simple experiment where a red laser beam shines through a clear glass filled with water. Students then observed how adding drops of milk causes the laser beam to transform into a fireball of light at the beginning of the glass, instead of passing through the water as a straight line. It was explained that the fat solubles in milk scatter light, hence creating a fireball affect. It was also explained that reading the content of a poster, paper, etc., from any viewpoint is the result of scattering. In this case, light is not reflected as this would make the object appear bright and shiney like a mirror.

• Lastly, students learned that refraction is similar to transmission except that it involves the bending of light as it passes through an object. This was demonstrated through a simple experiment where students observed how a straw appears to bend when placed in a glass of water. Examples of real-life objects that refract light include diamonds and prisms.

The remainder of this module focused on the use of lenses. Students learned the definition of lens as a transparent material with generally two (or more) curved surfaces that refract light. They learned how light is refracted for both concave and convex lenses, as well as terminology covered in their textbooks—such as focal point and length, optic centre, principal axis, radii of curvature, etc. Students learned that convex lenses magnify objects because they converge light rays, whereas concave lenses minimize objects because they diverge light rays. This was demonstrated by using a water droplet to magnify the text on a newspaper, and looking through convex and concave lenses purchased from a science lab store. Students also learned the meaning of a virtual focal point and how this applies to the image created by a concave lens. In fact, students were able to measure the virtual focal point of a concave lens by devising an experiment of their own!

Lastly, to conclude the unit, we discussed the various uses of lenses in our daily lives. Students mentioned how lenses are used to make cameras, binoculars, microscopes, and telescopes. They enjoyed a presentation, also prepared by Professor Chandrasekaran, on magnifying powers, which showed a view from the world from the largest possible distance (outer space) to the closest possible distance (inside the cells of a leaf). This presentation beautifully illustrated the ability of lenses (and light) to guide our vision and overall experience of the world! 

Overall, students enjoyed the activity-based nature of this program. Moreover, they easily picked up concepts in their textbooks once they were supplemented with hands-on activities. This ranges from understanding the meaning of light and the role it plays in our daily lives, to realizing what a convex or concave lens looks like and can do! Education ultimately boils down to making the subject matter accessible and engaging to our students, and we hope to have accomplished this here. Sackhumvit Trust would like to thank DSF for enabling us to conduct these lessons as part of its after-school tutorial program at the Yeshwantpur and R.T. Nagar education and development centres. Sackhumvit Trust is happy to share these resources with other schools and organizations dedicated to the education of underprivileged youth.