PHY 112 Lab 11 - Sofia Villamil Quintanar

PHY112 Lab 11 Name: Sofia Villamil Quintanar Lenses Section: 26190 Part 1 - Lens Simulation Access the Lenses and Mirrors interactive at The Physics Classroom site for Part 1 of the lab. Setup: Choose “Lens” and Converging” for the simulation. Choose the “arrow” object. Use the “focus” slider to choose a lens focal length between 20-25 cm. Record the focal length above the data table below. Do not change the focal length while recording measurements in the data table. Use the “height” slider to choose a height of the arrow object between 15-20 cm. Record the object height above the data table. Do not change the object height while recording measurements in the data table. Positioning the object: Note where the “f’ and “2f” positions are on the object side of the lens, and drag the arrow object to positions consistent with the values in the data table. Record the Object distance in cm for each of the object positions in the data table. Take a screenshot: With the object position at 2 f > d o > f , and all 3 rays on, take a screenshot of the simulation. Paste it below on the worksheet where indicated. Observing the images: Observe the image characteristics, including the image distance (d i ), image height, and image position (either to the left or the right of the object position). Note that a negative image height indicates an inverted image. Note also that a virtual image occurs when the object and the image are on the same side of the lens. Record the observations in the data table.

Part 1 Data Table: Object Height: 17.6 cm Focal length: 23.8 cm Object characteristics Image characteristics Object position ( d o ) relative to focal length ( f ) Object distance (cm) Image distance (cm), height (cm), and position (left or right of object) Larger, smaller, or same size as object Inverted or upright Real or virtual d o > 2 f 60.4 Distance: 39.4 Height: -11.4 Position: right smaller inverted real d o = 2 f 47.9 Distance:47.5 Height: -17.4 Position: right smaller Inverted real 2 f > d o > f 40 Distance: 58.8 Height: -25.7 Position: right larger inverted real d o = f 23.8 Distance: infinity Height: infinity Position: none none none none 3/4 f ˃ d o ˃ ½ f 77.5 Distance: 34.4 Height: -7.7 Position: right smaller inverted Real ½ f ˃ d o 9.7 Distance: 16.2 Height: 29.5 Position: left larger upright virtual Screenshot : Paste the screenshot of the simulation at the 2 f > d o > f object position below:

Part 2 – Physical Lab 1. Place the lens a few centimeters away from some printed text. Look through the lens. What do you observe? Is this information consistent with the simulation observations? Explain. 2. Steadily move the lens towards you (further away from the printed text) while looking through the lens. What do you observe? Is this information consistent with the simulation observations? Explain. 3. During the previous lens motion, there should have been a position when no image of the printed text was observable. Review your observations from the simulation. What is the significance of this position? Explain. 4. Explain how you can use the previous observations to determine the focal length of the lens. Use a ruler or meter stick to find the focal length. Report your process and the final value below. When the lens is placed a few cm away, the text is legible and appears to be the same size as when there is no lens. This is consistent with what I saw in the simulation, when the object was in the 2F position, the object and image appear to be the same size. As the lens was moved further away from the object, the letters appeared to increase in size and they became less legible, the image was then blurry. This is not what is expected from what I saw in the simulation, the image got smaller in the simulation while the text now got larger through the lens. This position is at d0 = F, this the the point in which the light from the lens does not converse. It is refracted and it can’t form an image. I found the focal point to be 16 cm. I then made a small dot on a piece of paper and started with the lens being close to the piece of paper. I then slowly began to move the lens towards me until I could no longer see the dot on the piece of paper. I then measured the distance between the paper and the lens and found that it was 16 cm.

5. Another method that could be used to solve for the focal length of the lens is the relationship between the object and image positions. Use the fine point dry or wet erase marker in your lab kit to draw an arrow on the face of the flashlight from your lab kit. Alternatively, you could remove the curved lens and tape on a piece of flat plastic or glass. Shine the flashlight on a wall or other surface. You may see a shadow of the arrow you drew, but you will not see a focused image on the wall. Explain why. 6. Place the lens from the kit in front of the flashlight. Since you want to produce a real image, make sure the flashlight isn’t too close to the lens. Adjust the d o value until you see a focused image of the arrow appear on the screen or wall (see below). Measure the d o and d i values using a ruler or meter stick. Record your d o and d i values below. Remember to include units. d o di flashlight lens wall or screen The light rays appear to be scattered as soon as it hits the lens, there is no focus for the image because the rays don’t converge. D0 = 32 Di = 30