Lab 10Optics Odds and Ends

OBJECTIVESExplore conceptual odds and ends of optics not covered in lecture.

EQUIPMENTOptics stuff

Part 1: Microwave Polarizationa. A microwave transmitter emits polarized microwaves and is detected by a

microwave detector. Setup the transmitter, polarizing grating and detector as shown on the right.

b. Measure the relative intensity as the angle θ of the polarizing grating is rotated from 0o to 180o.

Optical Polarizationc. Using a light source and an optical polarizer, shine light off of glass and rotate the polarizer

similar to part (b). Is the light reflected from the glass polarizer?

Part 2: The Eye Modela. Farsighted Eye

A person affected with hyperopia has a shorter-than-normal eye ball, making the retina too close to the lens system. This causes images of near objects to be formed behind the retina. Move the retina screen to the normal slot and find the near point (NP) using a light

source. Now move the retina screen to the far slot and describe the image a farsighted person

sees? Move the eye model away from the light source. Does a far-sighted person have trouble

seeing distant objects? Move the eye model back to the NP and correct the hyperopia by putting eyeglasses on

the model. Find a lens that brings the image into focus when you place it in front of the eye in slot 1.

b. Nearsighted Eye A person affected with myopia has a longer-than-normal eye ball, making the retina too far away to the lens system. This causes images of far-away objects to be formed in front of the retina. Move the retina screen to the normal slot and find the near point (NP) using a light

source. Now move the retina screen to the near slot and describe the image a nearsighted

person sees? Move the eye model away from the light source. Does a near-sighted person have

trouble seeing distant objects? Correct the myopia by putting eyeglasses on the model. Find a lens that brings the

image into focus when you place it in front of the eye in slot 1.

Part 3: Color addition.We have hung a white screen on the side wall of the lab, and illuminated it with three overlapping spotlights (R, G and B, of course).

For each of the cases below, predict what you will see, then check your prediction.

Combination of colors Predicted Color Observed Color

Red and Blue ___________________________________________________________________ Blue and Green ___________________________________________________________________ Red and Green ___________________________________________________________________

All Three ___________________________________________________________________

Note: We have technical terms for these overlapping colors: “blue-green” = cyan, purplish, or “red-blue” = magenta, and “yellow” = yellow.

Experiment with making shadows on the wall (with all three lamps together), by putting a pencil or other object in one or more of the colored light beams. Can you explain the colors you see?

Part 3: Light from warm objectsAll objects emit light. As an object gets hotter, it emits more light and it emits light of higher energy (thus higher frequency and shorter wavelength). Warm objects emit mostly infrared light, IR, which we can’t see, but this special camera can ‘see’ infrared light!

Use the camera and your eyes to answer the following questions: Which emits more IR light – your eyes, or your nose? Why?

Look at a cup of hot water vs a cup of cold water. Which one emits more infrared light?

If we heat something until it gets really hot, do you think it could emit visible light?

Turn on the wire coil and watch it warm up. Does it emit visible light? _____What color does it emit? _______ Is it still emitting infrared light as well? ______

If we heat up something even more, what will happen to the wavelengths of light it emits? Use the light bulb filament. Turn up the voltage on the light filament and describe how its light changes.

While you have the camera in your hand, see if IR light passes through these materials.Predict first!

clear acrylic glass black plastic paperDoes IR go through? Prediction: ________ ________ ________ ________

Test result: ________ ________ ________ ________

Part 5: Energy in lightHere we have some fluorescent materials. Light can excite these materials and cause them to glow, but it has to have enough energy to do so. Try different kinds of light to see if they have enough energy to excite the fluorescent material. Does it cause fluorescence?Light Color Prediction Observation

Infrared (warm light bulb)

Red light (red laser)

Green light (laser)

Violet light (laser)

Ultraviolet light (UV lamp – wear goggles)