REFLECTIONS OF YOU (DO IT AT HOME LAB)
NAME__________________________ PARTNER ____________________ DATE___________
PURPOSE
To find the relationship between the angle between two plane mirrors and the number of images visible in the mirrors.
MATERIALS
Two plane mirrors, object to view.
PROCEDURE
1. Set the two mirrors vertically on a piece of white paper on the table, support them against a book. The two mirrors should form a straight line; that is the angle between them should be 180 degrees
2. Use or construct out of paper a small object on which the letter "R" is written. Draw a line perpendicular to the two mirrors at the joint. Set the object on this line a few centimeters from the mirrors.
3. Look into the mirrors and determine how many images of the "R" you can see in the mirrors Also, determine if the images of the "R" are inverted vertically or laterally.
4. Reduce the angle between the mirrors while watching the image(s) for any changes in number or orientation. Record the angles and orientations for the angle(s).
5. Make a ray diagram for the path of the light rays from the object to your eyes.
6. Repeat steps 3 and 4 (and 5 if you can) for several angles.
7. From your chart of images angles and orientations, find a mathematical formula which relates the number of images to the angle between the mirrors for all the angles you recorded. Also determine a rule that allows prediction of the image orientation from the angle. Use your formula to predict the number of images (of each orientation) for some angles you did not record. Check your predictions by experimentation. Revise your formula if necessary, and repeat. If your formula appears successful, check with others to see if they can confirm your results. Your formula/description should include instructions for rounding off fractions; since there are no real fractions of very small images. If your formula is carefully done; it should be possible to write a computer program that allows the user to input an angle; then the program calculates and returns the number of images. (Optional: try it.)
! DATA
Angle No. Of Inverted Images No. Of Normal Images Total No. of Images
ANALYSIS / CONCLUSION
Explain how this experiment illustrates the scientific method.
And:
INDEX OF REFRACTION
NAME________________________ PARTNER ___________________ DATE ________
PURPOSE
To determine the index of refraction of glass and other substances.
MATERIALS
Circular water tank, Glass plate about 7 cm square, prism, pins, protractor, plain paper Laser.
Precaution: EVER LOOK DIRECTLY INTO A LASER BEAM. Always keep the beam aimed toward the wall or below eye level.
INTRODUCTION
The index of refraction of a substance is defined as the ratio of the speeds of light in the two media. Using Snell's law the index "n" can be determined from angle measurements.
PROCEDURE
1. Place the glass square flat on the center of a sheet of plain paper; outline it with a sharp pencil. St the Laser on the lab table, then set the glass and paper on a book so that the laser beam will shine trough the glass. Don't be confused by the reelections inside the glass or plastic. ALWAYS AIM THE LASER TOWARD THE WALL AND BELOW EYE LEVEL. Aim the Laser at an angle about 1.0 cm from one corner of the glass plate; adjust the angle so the beam exits the plate on the opposite side near the opposite corner. Then place pin A at the point where the beam leaves the glass plate. Next place a pin (B) where the beam enters the glass; lastly place a pin (C) in the beam at least 7 cm nearer the Laser so the line BC will be the incident ray. The line BA is the refracted ray.
2. Turn off the laser, remove the glass and mark the pin positions; remove the pins. Draw a circle with B as the center. The circle should be 8-15 cm in diameter.
3. Draw the path of the light ray C-B-A as a dark line. Draw in the Normal at B. Complete the diagram as shown below.
4. Measure the lengths X, Y and the angles i, r and record.
5. Use the data to find the index of refraction two ways. Notice that sin i = X/R where R is the circle radius. Similarly sin r = Y/R
6. In a similar way use the triangular glass plate to find its index. The Laser is Red but if you look at white light you should notice a very slight difference between the bending of light of different colors.
7 Use the circular refraction tank find the index of refraction of water.Make at least five trials for light incident from air to water, measure and record i and r for the angles,
8. Repeat for five angles from water to air. One of the angles should be the angel that makes r 90°.
! DATA
MATERIAL X Y n=X/Y i r sin i /sin r
Triangle
Square
Refraction Tank Air (i) Water(r) Water(i) Air(r)
1
2
3
4
5
6
ANALYSIS / CONCLUSION
1. Complete your diagrams and include them with your report.
2. In Excel plot a graphs of sin r as a function of sin i. Enter the r data in the leftmost column so that it will plot on the x-axis. Try to put both sets of data on the same graph. Then fit a trendline that is forced throuh 0.0 to each data set; find the slope of each graph and compare to the values you expect for the index of refraction.
3. If the incident angle is 0.0 degrees, the angle of refraction is always _________.
4. What is the measured critical angle for water ._______. How does it compare with the value calculated from the index of refraction.
And:
Physics Lab Extension
Critical Angle & Total Internal Reflection
Objective: Determine critical angle for substances using Snell's Law
Materials: laser, beam splitter, glass, lucite
Methods
1. Establish monochromatic beam through prism & rotate until angle of refraction is 90 degrees.
2. Measure angle of incidence inside substance.
3. Accurately draw all angles and fully label.
Analysis
1. Using Snell's Law, calculate index of refraction for each substance.
2. Determine the critical angle for diamond, water, corn oil.