through a Glass Block
Objective: Trace a refracted light ray through a glass block and calculate the index of refraction
Materials: glass block, pins, board, ruler, protractor
1. Lay the glass block flat on your paper, then carefully outline its shape.
2. Draw a normal line z to one of its sides then place a pin at the intersection of the normal line and the surface of the block. Label as point R.
3. Measure an angle of 10-15o from the normal line, then place a pin at point A approximately 6-8 cm from the block along your selected angle.
4. Look through the other edge of the block. Place a pin against the edge of the block at point A2, and another pin E (for your eye) 6-8 cm from the block in line with A, R, and A2. Be sure to label all points (A, R, A2, E).
5. Repeat for angles of 20-25o (B, R, B2, E) and 30-35o (C, R, C2, E).
6. Trace the various rays using arrows to show the path of the light from the pins A, B, and C.
7. For each angle, calculate the index of refraction n of the glass block using Snell=s Law (n1Sinθ1 = n2Sinθ2)
8. Determine the speed of light in the glass block. Determine the wavelength of red and blue light in the glass block if in air the wavelengths are 7 x 10-7 m and 4 x 10-7 m, respectively.
9. Calculate the critical angle of the glass block.
10. Place the block vertical on your board such that one of the letters shows through the long end. Now estimate the position of the letter along the vertical side of the block. Have your partner measure the distance down. Estimate the index of refraction as the length of the block/distance down.
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