CONVERGING LENS

Psalms 34:3 O magnify the LORD with me, and let us exalt his name together.

Ezekiel 38:23 Thus will I magnify myself, and sanctify myself; and I will be known in the eyes of many nations, and they shall know that I am the LORD.

OBJECT:

To fined the focal length of a double-convex lens.

MATERIALS:

One large square can, last resort square can from olive oil, because of the oil coating, you will have a difficult time working with it. Can opener, A 60 - 75 watt light bulb, and socket, Extension cord, White paper, White stiff paper ( like index card ) with a metric strip of about 7 cm in length; Two screen supports, A lens with it support jacket, Two foot PVC pipe with metric strip attached, Leg supports from SBB, Opaque 5 cm object, preferable from black construction paper, A PVC " T " connector, modified, by cutting a half section from top of it ( you will need vice and a hack saw for the modification).

NOTE ABOUT LENSES:

Try to obtain two lenses, small magnifying lenses of different strength. These will have very small value for 2F. Only commercial lenses would have significant higher values for 2F.

PROCEDURE AND OBSERVATION

1. Construct the set up shown below.

2. Obtain tape and cut your 5 cm high arrow, preferable from black construction paper.

CAUTION:

Use caution, because of the sharp metal that is in side the can! If necessary use protective gloves!!

3. Insert your lamp through the opening and then thread your plug through the spout in the can. Over the opening of the can, tape a piece of white paper. Later you will tape on an object arrow to this paper.

4. Place the metal can at the zero end of the two foot beam ( with metric strip ).

5. Insert your lens with its lens holder into the plastic support. Slide the lens support close to the white paper, so that you can get a rough idea as where to attach the black object arrow, so that it is the same height as the lens.

6. Insert your screen into the screen support, with the metric strip facing the lens.

7. Dim the lights, turn the lamp on and you are ready to start. Adjust the lens and the screen, until the image shown on the screen is the same size, as the object; Which should be 5 cm high, be sure to make use of the metric scale that is attached to the screen.

8. When the object and the image are the same size, they both must be located at 2F or twice the focal length. Therefore the distance between the object and the lens should be equal to the distance between the lens and the image.

9. The distance between object and the lens is __________.

10. The distance between lens and image is ___________.

QUESTIONS:

1. Define a real image.

2. Define a virtual image.

3. What is the speed of light in air?

4. What is a normal?

5. What happens to light rays, when the speed of light is reduced, with respect to the normal?

6. What happens to light rays with respect to the normal, when the speed of light is increased?

7. Why are light rays refracted by a lens?

8. What kind of image will you obtain, when the object is greater then 2F?

9. What kind of image will you obtain, when the object is at 2F?

10. What kind of image will you obtain, when the object is between 2F and F?

11. What kind of image will you obtain, when the object is at F?

12. What is the focal length of your first lens?

13. What is the focal length of your second lens?

14. Compare a convex and a concave lens.

CAUTION: Because the light bulb is in a confined space the can will get hot, so every chance that you get, turn light bulb off, when not in use!

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