- 01 Apr, 2021
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Geometric Optics
What to Turn In
► Analysis Questions
► Data Tables 1-4
► Graph of dimage vs. dobject for the convex mirror. This includes data for 2 different focal lengths.
Given a lens of any shape and index of refraction, you could determine the shape and location of the images it forms based only on the Law of Refraction. You need only apply the law along with some of the ray tracing techniques you have already used. However, for spherical lenses (and for spherical mirrors as well), there is a more simple equation that can be used to determine the location and magnification of an image. This equation is called the Thin Lens Equation (Note: it is also sometimes called the Fundamental Lens Equation):
(1)
where f is the focal length of the lens, and do and di are the distances from the mirror to the object and image respectively (see Figure PH11.5). The magnification of the image is given by the equation:
(2)
Part A: Mirrors
Here we will use curved mirrors to focus reflections and form images. Begin by visiting the simulation at the following website:
https://www.physicsclassroom.com/Physics-Interactives/Refraction-and-Lenses/Optics-Bench/Optics-Bench-Refraction-Interactive
The simulation will open and look like the image below. To increase the size of the simulation, there is a button in the top-left to put it in full screen mode, or you can click and drag the bottom-right corner to expand the size to what you want.
Getting Acquainted
By default, Optics Bench opens in Lens mode. Click on the Lens button in the middle to change to Mirror mode. You should observe a curved mirror with its principal axis, a candle, and three sets of incident and reflected rays.
Experiment with the simulation in the following ways:
• Tap and drag the candle back and forth along the axis; observe how the image changes.
• Use the focus slider to change the focal length. Notice how f and 2f change location. The 2f point is the Center of Curvature location.
• Use the height slider to change the image height.
• Notice how the object can be changed into an arrow or a vertical column of letters (A B C).
• Notice how the incident rays can be toggled ON and OFF.
• Notice how the object can be dragged to the right side of the mirror – the convex side.
Observations
⦁ Concave Mirrors
Use the sliders to set the focal length to approximately 30 cm and the object height to approximately 20 cm.
Then drag the object to the various locations described in Data Table 1. For each location, practice the L.O.S.T. art of image description – that is, describe the image Location, Orientation, Size, and Type.
Data Table 1 already has descriptors of what you should record. Remove what you don’t need in each cell. For example, the Orientation column has the descriptors Upright and Inverted. If an image is inverted for your observation, you would remove the word Upright.
(Remember, real Images are formed when reflected rays converge at the image location. Virtual images are formed with light rays diverge after reflection.)
2. Convex Mirrors
Use same values of focal length and object height. Drag the object to the right side of the mirror and observe the image. The right side of the mirror is the convex side.
Do the basic characteristics of the image depend upon where on the right side of the mirror that the object is placed? Experiment to find out.
Practice the same L.O.S.T. art of image description for a nearby and distant object position. Record your observations using Data Table 2.