Physic II LAB

http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html

M7A1 Experiment: Optics

PART I - The Thin Lens Equation

Start the Geometric Optics Simulation (if you haven’t done so already) by clicking on the image below.

http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html

· Move the object so that the eraser is on the optical axis.

· From the green control box, select Many Rays.

The Many Rays setting allows you to see a depiction of light being diffusively scattered from the point of the pencil. Several of these scattered rays intersect the lens. Because the lens is curved, each ray encounters the surface of the lens at a slightly different angel. Snell’s Law tells us that each light ray is going to be bent at a slightly different angle. Here is where it gets interesting. The bent rays intersect each other at a location called the focal point of the lens.

The relationship between the object distance (p), the image distance (q), and the focal length (f) is captured by the thin lens equation

· Select the ruler from the green control panel.

· Choose any Radius of Curvature other than the default 0.8 m.

· Move the object to any position on the optical axis outside the focal length (e.g., beyond the “x”),

· Measure the image and object distances.

· Repeat 5 times.

In your laboratory notebook, create a table that contains the focal length, object distance, and measured image distance. In two additional columns, include the image distance calculated from the thin lens equations above and the difference between the two image distances. Also write a short paragraph describing whether or not your data and analysis supports or fails to support the thin lens equation.

Part II - Magnification

You have encountered a single convex lens before, and likely used it to focus the sun’s rays to burn leaves. This single convex lens is called a magnifying glass, and in this activity, we are going to find out how it works.

Conventions: An image height is positive if it is in the same orientation as the object. An image height is negative if it is inverted with respect to the object. All of our images to this point have been inverted. If you have been paying attention, you will also have noticed that the image height gets smaller as you move away from the focal point.

The magnification (m) of an image can be greater than one. In other words, the size of the image is larger than the actual size of the object. Magnification can also be smaller than one; the image will be smaller than the object. The formula which describes magnification is

· Check the box for Principle rays.

· Check the box for Virtual Image.

Experimentally determine the object distances for which the magnification is positive, negative, greater than one, and less than one. Record distances as greater than or less than the focal length. Be sure to write your results in your laboratory notebook.

Part III - The Lens Makers Equation

The thin lens equation is not the whole story. You can and should play with all of the controls to see how they affect the focal point of the lens. The Lens Maker’s Equation takes into account both the index of refraction of the lens material and the curvature of the lens surface itself. The form we have below is a special case of a more general equation, in which the radii of curvature (R) of both lens surfaces are equal to each other.

Experimentally determine the relationship between the index of refraction and the radius of curvature for a constant focal length.

· Ensure that the ruler is still present in the simulation.

· Choose a radius of curvature other than the default value.

· Change the index of refraction by some small increment.

Observe the change in the position of the focal point. Use the slider bar to change the radius of curvature to bring the focal point back to its original position. Record both the index of refraction and the radius of curvature in your laboratory notebook. Repeat the process of changing both the index of refraction and the radius of curvature to obtain at least 10 data points. Plot your data on a scatter plot using your favorite spreadsheet program. What is the shape of this curve? What happens to the required index of refraction as the radius becomes arbitrarily large or arbitrarily small? What conclusions can you draw about the material requirements of manufacturing small spherical lenses for use in personal electronic devices?