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Question

Lab 5 : Ray

Optics                                                   Name: _______________________

Do not delete content, bold and highlight your answers

Introduction:

When you hold your glasses far away from your face, what do you see? If you look through a magnifying glass and move it away from your face, something odd happens as you look through the moving lens. The light that reflects off images and passes through a lens before it arrives at your eye can be simulated as a series of rays. The lens we will use in this simulation is a thin double-convex lens.

Important Formulas:  or    or

Please note that in some texts, the object's distance is given by "p" and the image's by "q"

Procedure: Go to http://phet.colorado.edu/en/simulation/geometric-optics  and download the simulation. Save geometric-optics_en.jar as a file in a directory you can remember. Click on geometric-optics_en.jar in the download window. Accept the agreement and begin the simulation

PART I

1.      Take some time and familiarize yourself with the simulation. You are able to move the object and the lens and change the characteristics of the lens. During this lab, be sure to always anchor your image on the principal axis. The pencil's eraser works well for this.

2.      Click  to draw the rays using the 3-ray system you learned in your book (Figure 17.16 on page 365).

3.      Move the object towards the lens. What happens to the image formed on the other side of the lens?

4.      As you move the object inside the lens' focal point (marked by the 'x') something odd happens. The rays don't meet, they diverge. Does this mean no image will be formed? 5 pts [Answer

Where is the image? Recall figure 17.17 from the text.

5.      Click on "Virtual Image."

(a) How are a real image and a virtual image similar? 5 pts [Answer]

(b) How are they different? 5 pts [Answer]

6. Click on the ruler. You will need to make several measurements during the lab. You may, if you wish, leave your measurements in cm when using the formulas given above.

PART II

Set the lens's refractive index (n) to 1.8 and the radius of

curvature (R) to 0.7m.

1. Use the appropriate equation above to solve for the

focal distance (f). Show your work below

(Measure the focal distance to confirm your answer.)

2. Using the focal distance you just found, complete the table below and check your work in the simulation.

10 pts

Focal Distance (f)

(cm)

Distance Object (do)

(cm)

Image Distance (di)

(cm)

Magnification

(m)

120. cm

90. cm

60. cm

30. cm

15 cm

3. Repeat the previous exercise, but with a very

different lens with the following characteristics:

R = 80cm, n = 1.25

10 pts

NEXT PAGE ..........

WATCH YOUR SIGNS (Bold the correct answer and highlight)  Real images' (di ) should be __+ / - __ while virtual images (di) should be __+ / -__

Focal Distance (f)

(cm)

Distance Object (do)

(cm)

Image Distance (di)

(cm)

Magnification

solve for this first

120. cm

90. cm

60. cm

30. cm

15 cm

Conclusion Questions and Calculations:   Highlight your correct answer and show your work for numerical questions.

1.      Images found behind a lens are ( real / virtual ) images that will be ( upright / inverted ). (1 pt)

2.      As the radius of curvature of the lens increases, the focal point of that lens becomes ( closer to / further away from )  that lens. (1 pt)

3.      As the refractive index of the lens increases, the focal point of that lens becomes ( closer to / further away from ) that lens. (1 pt)

4.      What advantage does a larger lens have over a smaller lens (all other characteristics being equal)? (5 pts)

5.      What was the focal distance (f) when the radius of curvature was 0.70 and index of refraction was 1.8? _____________ (5 pts)

6.      Calculate the radius of curvature of a lens with a focal distance of 40. cm and an index of 1.2. ____________________ (5 pts)

7.      An object placed 35. cm away from a lens projects a real image 0.55m behind the lens. What is this lens' focal distance? _____________________(5 pts)

8.      What is the lens' magnification? ____________________(5 pts)

9.      An object 20. cm to the left of a convex lens is 1.0 m in height. What is the height and location of its image if the lens has a magnification of -2.0? ________________ m and ________________ cm on the ( left / right ) side of the lens (5 pts)

10.  Imagine you are nearsighted (can only see close objects clearly and far objects are blurry). At your last eye doctor's appointment, your optometrist tells you that she will need to increase your prescrition because as it turns out light is focusing "too soon" or in front of your retina. You respond, "Obviously, I will need a ( converging / diverging ) lens with a ( higher / lower ) focal distance." (5 pts)

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