Introduction to Chemistry and Physics
Introduction to Chemistry and Physics
Light
Objectives of this lab:
1. Describe how light interacts with lenses.
2. Explain how colors are perceived and how they mix.
3. Draw a light ray diagram to explain how a mirror works.
Procedures:
Discuss each part with your partner. Do not go on to other parts of the lab until you and your partner are sure you understand. Ask your instructor about anything you are unsure of. Although you work with a partner, be sure you can do all parts of the lab on your own, because you will have to on a test.
ALWAYS USE CORRECT UNITS on any numbers you write down!
Please be gentle with all the equipment so we can have it to use later on.
1. Use the magnifier to observe a few objects. Do NOT touch the lens because your finger smudges will interfere with how well you can see! Describe one thing you can see with the lens that you could not see without it below.
Now look at the “tails” side of a penny. Describe what you see inside the Lincoln Memorial.
2. Now hold the lens at arms length and view something far away (across the room). When you use the magnifier like this, what does the lens do to the image?
3. There are a few other magnifying lenses in the room. When you get one, compare the magnification of it with the magnification of the lens you already had.
After determining which one can magnify the most, look at the lenses themselves. How do they compare?
4. Place a lamp so that the light shines straight down onto the floor. Hold your lens horizontally a few inches below your lamp. Move the lens up and down until you can clearly see an image of the bulb (you can actually clearly read the writing) projected onto the floor.
The distance that you need to hold the lens from the floor to get this image is called the focal length of the lens. Measure the focal length of your lens with a meterstick (in centimeters).
5. Now you will examine colors and their properties. Note that the colors of the visible spectrum are arranged in order: Red, Orange, Yellow, Green, Blue, and Violet. ROYGBIV is also the order you see colors in a rainbow. When the colors blend smoothly into each other, we call it a continuous spectrum. When all these colors are mixed together, you see white!
When colors mix, the effects are complicated. As you already know, there are several shades of every color.
When we see color, it is the reflection of that color (usually a mix of color). All other colors are absorbed. So when an object absorbs most of the yellow, green and blue light, the resulting color will appear red. Below are a few simple rules for the colors that are reflected by a given color.
White = R O Y G B I V are reflected
Red = R O V are reflected
Blue = G B V are reflected
Yellow = O Y G are reflected
If a color is not reflected by an object, it must be absorbed.
What colors are reflected by black?
What colors are absorbed by black?
6. Now you will try to make your own color filters. A filter is something that absorbs some colors and reflects or transmits others.
Use the bottles of colored water on the teacher’s desk. Fill four test tubes as follows: 1 with red, 1 with blue, 2 with yellow.
Predict what will happen when you pour the red and one yellow together.
The mixture becomes orange because the red pigment absorbs Y, G, and B while the yellow pigment absorbs R, B, and V. The only color that remains unabsorbed is Orange!
7. Predict what will happen when you mix the yellow and blue solutions. Explain your prediction using the rules given in part 5 of the lab.
Now mix the yellow and blue and see if you were correct.
8. Using the Law of Reflection, draw rays to show how light gets from the star to the mirror, and then to the eyes drawn below.
Make sure that the angle into the mirror equals the angle out of the mirror!
9. Using what you did above and still thinking about the Law of Reflection, design an experiment to find out the minimum size of a mirror you would need to see your whole self. Assume that the top of the mirror is even with the top of your head. Does the mirrors size depend on how close you are to the mirror?
Describe how you would set up an experiment to figure this out below. To help you figure this out you should first try to draw a diagram of you looking into a mirror. Draw lines to show the light that goes from your feet to the mirror and to your eyes. Then draw lines to show the light that goes from your head to the mirror then back to your eyes. Make sure that the angle into the mirror always equals the angle out.