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Anthony Nguyen

Leanne Lansangan

Angelique Delarazan

Period 2 Fiziks

2/27/11

Lab #15: PASCO Basic Optics System (1-17)

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Experiment 1: Color Addition

Part 1: Addition of Colored Light

Data Table:

|Color Added |Resulting Color |

|Red +blue + green |White |

|Red + blue |Red |

|Red + green |Yellow-orange |

|Green + blue |Teal/Turquoise |

Questions:

1. Is mixing colored light the same as mixing color paint? Explain.

Mixing the colored light is similar because the colors blend together when they are mixed.

2. White light is said to be the mixture of all colors. In this experiment, did mixing red, green and blue light result in white? Explain.

Yes, mixing red, green and blue light did result in white. This happened because the colors red, green and blue cover the basic colors that range from each color to color. It covers yellow, orange, purple, etc.

Part 2: Observing Colored Ink Under Colored Light

Data Table:

|Trial 1: Name of Observer: | | | | |

|Anthony | | | | |

|Color of Light |Line |Apparent Color of Ink |Do they look different? |Actual Color of Ink |

|Blue Light |A |Red |No |Red |

| |B |Black | |Black |

|Red Light |C |Black |Yes |Black |

| |D |Black | |Blue |

|Trial 2: Name of Observer: | | | | |

|Angelique | | | | |

|Color of Light |Line |Apparent Color of Ink |Do they look different? |Actual Color of Ink |

|Blue Light |A |Red |No |Red |

| |B |Black | |Black |

|Red Light |C |Black |Yes |Blue |

| |D |Black | |Black |

Look at red and black lines under red light. Which is easier to see?

Under red light, the black lines are easier to see.

Questions:

1. What makes red ink appear red? When red ink is illumined by blue light, is most of the light absorbed or reflected?

Red ink appears red because it reflects red light. When red ink is illuminated by blue light, most of it is absorbed.

2. When illumined with red light, why is red ink on white paper more difficult to see than black ink?

When illumined with red light, red ink is harder to see because the color is reflected on an exact or very similar color.

Experiment 2: Prism

Questions:

1. Rotate the trapezoid until angle (Ө) of emerging ray is as large as possible until the ray separates into colors.

a. What colors do you see? In what order?

Purple, blue, red, white, and yellow are seen in order from left to right.

b. Which color is refracted at the largest angle?

Blue is refracted at the largest angle.

c. According to Snell’s Law and the information given about the frequency dependence of the index of refraction acrylic, which color is predicted to refract at the largest angle?

Blue is predicted to refract at the largest angle because it has the largest index of refraction.

2. Without repositioning the light source, turn the wheel to select the three primary color rays. The colored rays should enter the trapezoid at the same angle that the white ray did. Do the colored rays emerge from the trapezoid parallel to each other? Why or why not?

No, the color rays emerge from the trapezoid perpendicular, at a right angle, to each other. This is because the rays have varying indices of refraction.

Experiment 3: Reflection

Part 1: Plane Mirror

Data Table:

|Plane Mirror Results | |

|Angle of Incidence |Angle of Reflection |

|16° |13° |

|21° |15° |

Questions:

1. What is the relationship between the angles of incidence and reflection?

The relationship between the angles of incidence and reflection is that they have the same angle.

2. Are the three colored rays reversed left-to-right by the plane mirror?

No, the three colored rays are not reversed left-to-right by the plane mirror.

Part 2: Cylindrical Mirrors

Data Table:

|Cylindrical Mirrors Results | | |

| |Concave Mirror |Convex Mirror |

|Focal Length |7 cm |8.3 cm |

|Radius of Curvature (determined using compass) |14.7 cm |16.9 cm |

Questions:

1. What is the relationship between the focal length of a cylindrical mirror and its radius of curvature? Do your results confirm your answer?

The radius of curvature of a cylindrical mirror equals twice the focal length. The results confirm this relationship.

2. What is the radius of a plane mirror?

The radius of curvature of a plane mirror is infinite. This is because the image of a plane mirror is always virtual. Also, the image is “behind” the mirror, the same distance as the object in front of the mirror.

Experiment 4: Snell’s Law

Data Table:

|Angle of Incidence |Angle of Refraction |Calculated Index of Refraction of Acrylic |

|45° |30° |1.175 |

|55° |35° |1.000 |

|56° |34° |1.917 |

| | |Average: 1.364 |

Analysis:

1. For each row of the table, use Snell’s Law to calculate the index of refraction, assuming the index of refraction of air is 1.0.

2. Average the three values of the index of refraction. Compare the average to the accepted value (n = 1.5) by calculating the percent difference.

Questions:

1. What is the angle of the ray that leaves the trapezoid relative to the ray that it enters it?

The angle of the leaves the trapezoid should be equal to the ray it enters it.

Experiment 5: Total Internal Reflection

Data:

1. Record the critical angle here:

θc = 69° (experimental)

2. Calculate the critical angle using Snell’s Law and the given index of refraction of Acrylic (n = 1.5). Record the theoretical value here:

θc = 67.7° (theoretical)

3. Calculate the percent difference between the measured and theoretical values:

% Difference =

Questions:

1. How did the brightness of the internally reflected ray change when the incident angle changes from less than θc to greater than θc?

The brightness of the internally reflected ray becomes brighter when the incident angle changes from less than θc to greater than θc.

2. Is the critical angle greater for red light or violet light? What does this tell you about the index of refraction?

The critical angle is greater for red light. This shows that the index of refraction is smaller.

Experiment 6: Convex and Concave Lenses:

Data Table:

| |Convex Lens |Concave Lens |

|Focal Length |12 cm |6.25 cm |

1. Are the outgoing rays converging, diverging or parallel? What does this tell you about the relationship between the focal lengths of these two lenses?

The outgoing rays are parallel. This shows that the focal lengths of the lenses are opposites—one is negative, one is positive.

2. What is the effect of changing the distance between the lenses? What is the effect of reversing their positions?

The effect of changing the distance between the lenses is that when they are apart, they converge. When they are switched, it remains to be converged.

Experiment 7: Hollow Lens

Data Table:

|Predictions and | | | | | |

|Observations | | | | | |

|Lens Surrounded by: |Section 1 Filled With: |Section 2 Filled With: |Section 3 Filled With: |Prediction (converging |Observation (converging|

| | | | |or diverging) |or diverging) |

| |Air |Water |Air |Converges |Converges |

| |Water |Air |Water |Diverges |Diverges |

| |Water |Air |Water |Diverges |Diverges |

Questions:

1. Under what conditions is a plano-convex lens converging? Under what conditions is it diverging?

The plano-convex lens is converging whenever section 1 is filled with air. It is diverging whenever the section 1 is filled with water.

2. If a plano-concave lens of an unknown material is a diverging lens when surrounded by air, is it possible to know whether the lens will be converging or diverging when placed in water? Explain.

Yes, because when the object is surrounded by air, it usually converges.

Experiment 8: Lensmaker’s Equation

Data:

1. Measure the distance from the center of the lens to the focal point. Record the result as a negative value.

f = 11.5 cm (measured directly)

2. Measure the distance from the lens surface to the point where the reflected rays cross. The radius of curvature is twice this distance. Record the radius of curvature.

R = 12.8

3. Calculate the focal length of the lens using the lensmaker’s equation. The index of refraction is 1.5 for the acrylic lens. Remember that a concave surface has a negative radius of curvature.

f = 12.8 cm (calculated)

4. Calculate the percent difference between the two values of f from step 3 and step 5:

% difference = 10%

Experiment 11: Dispersion

Analysis:

1. At what angle of refraction do you begin to notice color separation in the reflected light?

At 25°, you begin to notice color separation.

2. At what angle of refraction does the maximum color separation occur?

Angle of refraction is at 78° when the maximum color separation occurs.

3. What colors are present in the refracted ray? (order from minimum to maximum angle of refraction.)

The colors present are red, orange, yellow, white, blue, and violet.

4. Use Snell’s Law to calculate the index of refraction of acrylic for red light (nred) and the index of refraction for blue light (nblue).

With an incident angle of 45°, the blue refracted at 78° and the red at 73°; therefore nred = 1.488 and nblue = 1.910

Experiment 12: Focal Length and Magnification of a Thin Lens

Part 1: Object at Infinity

Data:

1. Record the image distance.

di =43 cm

Analysis:

1. As d0 approaches infinity, what does 1/d0 approach?

2. Use the Thin Lens Formula to calculate the focal length.

f = 10cm

Part II: Object Closer Than Infinity

Part A: Focal Length

Data Table:

|Image and Object | | | | | | |

|Distance | | | | | | |

|Distance From Light|d0 |di |1/d0 |1/di |Image Size |Object Size |

|Source to Screen | | | | | | |

| |11.2 cm |86 cm |0.089286 |0.011628 |76 mm |10 mm |

| |11.5 cm |81.1 cm |0.086957 |0.01233 | | |

| |11.9 |68.2 cm |0.084034 |0.014663 | | |

| |12.2 cm |63.3 cm |0.081967 |0.015798 | | |

| |12.3 cm |16.0 cm |0.081301 |0.0625 | | |

| |12.5 cm |

| |F |

|Result from x-intercept |9.21 cm |

|Result from y-intercept |10.1 cm |

|% difference between results from intercepts |8.9% |

|Average of results from intercepts |9.66 cm |

|Result from Part I |10 cm |

|% difference between Average of results from intercepts and result |0.34% |

|from Part I | |

Analysis:

1. Calculate 1/d0 and 1/di for all 12 rows in the table above.

2. Plot 1/d0 versus 1/di and find the best fit line (linear fit).

y-intercept = 1/f =.099

x-intercept = 1/f = .1086

Part B: Magnification

Data:

| |Point 1 |Point 2 |

|M calculated from image and object distances |1.262 |7.6 |

|│M│ calculated from image and object sizes |1.262 |7.6 |

|% differences |0% |0% |

Questions:

1. Is the image formed by the lens upright or inverted?

The image is formed by the inverted lens.

2. Is the image real or virtual? How do you know?

The image is real because it can be seen on the screen.

3. Explain why, for a given screen-to-object distance, there are two lens position where a clear image forms.

There are two focus points because there are inverse relations between the object size and object distance.

4. By looking at the image, how can you tell that the magnification is negative?

If the image is inverted, the magnification is negative.

5. You made three separate determinations of f (by measuring it directly with a distant object, from the x-intercept of your graph, and from the y-intercept). Where these three values equal? If they were not, what might account for the variation?

We do not know the answer to this specific question.

Experiment 13: Focal Length and Magnification of a Concave Mirror

Part I: Object at Infinity

Data Table:

|Image and Object | | | | | |

|Distances | | | | | |

|d0 |di |1/d0 |1/di |Image Size |Object Size |

|45.0 cm |5.5 cm |0.0222 |0.0181818 | | |

|35.0 cm |5.9 cm |0.028571 |0.0169492 | | |

|25.0 cm |6.4 cm |

|M calculated from image and object distances |0.3125 |

|│M│ calculated from image and object sizes |0.3121 |

|% differences |0.128% |

Questions:

1. Is the image formed by the lens upright or inverted?

The image is inverted.

2. Is the image real or virtual? How do you know?

It is real because it is visual on the screen.

3. Explain why, for a given screen-to-object distance, there are two lens position where a clear image forms.

There are two focal points because there are inverse relations between the object size and object distance.

4. By looking at the image, how can you tell that the magnification is negative?

The magnification is negative because the image is inverted.

5. You made three separate determinations of f (by measuring it directly with a distant object, from the x-intercept of your graph, and from the y-intercept). Where these three values equal? If they were not, what might account for the variation?

We do not know the answer to this particular question.

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