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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 11.9 Practice - Ray Optics

Subsubsection Explanation Practice

Explanation 11.9.1. Ray Diagram.

Draw a ray diagram to determine the location of the images of both objects in the figure.
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Figure 11.9.1. Two objects and a mirror.
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Explanation 11.9.2. The Wall and the Mirror.

Shown below is an object, a wall, and a flat mirror.
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  • Find the image location
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  • Suppose you put your eye at each of the points on the right
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  • At which points would you be able to see the object?
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  • At which points would you be able to see the image?
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  • What direction would you have to look to see it in each case?
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  • Which rays is it necessary to draw to answer this questions?
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Figure 11.9.2. An object, a wall, and a mirror.
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Subsubsection A*R*C*S Practice

A*R*C*S 11.9.3. Fun House Mirror.

You go to the hall of mirrors in a funhouse and stand 2.25 m in front of a spherical mirror. The mirror forms an image of you at a point 1.25 m behind the mirror. What is the focal length of the mirror?
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Subsubsection Numerical practice

Calculation 11.9.4. Angle of Refraction.

Light traveling from water enters a horizontal slab of glass. The light makes an angle of 20° with respect to the horizontal surface of the glass. The indexes of refraction for water and glass are \(n_{water} = 1.33\) and \(n_{glass} = 1.52\text{.}\) Calculate the angle of refraction (in degrees).
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Answer.
\(55.3^{\circ}\)
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Calculation 11.9.5. Unknown Index of Refraction.

Light traveling from air strikes a horizontal slab of unknown material. The light makes an angle of 40° with respect to the perpendicular of the horizontal surface. The angle of refraction is measured to be about 29.4°. What is the index of refraction of this unknown material?
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Answer.
1.31
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Calculation 11.9.6. Total Internal Reflection.

At what minimum incidence angle (in degrees) will you get total internal reflection of light that is traveling from water into a layer of ice? Note that \(n_{water} = 1.33\text{,}\) and \(n_{ice} = 1.31\text{.}\)
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Answer.
\(80^{\circ}\)
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Calculation 11.9.7. Diverging Lens.

Consider a thin diverging lens with a focal length of 4 cm. A 2-cm-tall object is placed 8 cm in front of the lens. Use ray tracing to answer the following items:
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  1. Estimate the image distance in cm.
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  2. Estimate the image height in cm.
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  3. Estimate the magnification
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  4. Is the image real or virtual?
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Answer 1.
-2.2 cm to -2.8 cm
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Answer 2.
0.3 cm to 0.8 cm
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Answer 3.
0.1 to 0.4
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Answer 4.
Virtual
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Calculation 11.9.8. Magnifying Glass.

What is the focal length, in cm, of a magnifying glass (a thin converging lens) that produces a magnification of 3.00 when it is held 5.00 cm away from an object?
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Answer.
7.5 cm
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References References

[1]
Numerical practice activities provided by BoxSand: https://boxsand.physics.oregonstate.edu/welcome.
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