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Section2Newton's Opticks Experminents

Subsection2.1Experiment 1

Follow Newton's instructions for making the two-colored card (red and blue) using construction paper and glue. Be sure that the red/blue strip is on a black background. Place the card on the table and view it through the prism, as Newton suggests, by holding the prism close to your eye. Rotate the prism so that you can see the card in different orientations.

Note that the blue and red cards are shifted away from each other with the blue on the left being shifted up from the right red section. This agrees with Newton's observations. The shifting has to do with chromatic aberration and blue light being bent more than the red. We also noticed that there was a fairly pure red fringe on the red side but the blue was tinged with a wider spectrum; this would result from our blue being less pure than our red.

Subsection2.2Experiment 2

Wrap the card from Subsection 2.1 in black thread as described by Newton. Place your card upright and (in an otherwise dark room) illuminate it with a light source. Use one of the small lenses to project the card's image onto a blank white screen.

Observe that the thread comes into focus at a closer distance on the blue side than the red. This also occurs due to the difference in refraction for blue and red.

Subsection2.3Experiment 3

Obtain a ray box and a pair of prisms. Place the card into the end of the ray box that produces a single thin ray. Shine this ray into one prism. By doing so, we can obtain a full spectrum on a blank white screen some distance from the prism.

When a full rainbow is obtained, red appears on the left while blue to green to violet appear on the right. This occurs as a result of blue being refracted more severely than red. This is consistent with what was observed in Subsection 2.1

Starting with your spectrum, block every color but one (try red), shine the remaining single-colored beam through a second prism, and note what happens.

Refracted light of a single color remains a single color and thus Newton ascertained that the extent of refraction was a property of not only the mediums, but also of the type of light.

Go back to the full spectrum produced by a single prism. See if you can recombine colors by intercepting the spectrum with a second prism or a solid D-shaped plastic block.

We see that by using a converging block we are able to take the separated colors and recombine them into essentially the original light, as far as can be seen by the eye. This occurs due to the double refraction when moving from air to glass and back to air.

Figure2.1The splitting and then reconstitution of white light.