7: Optics and Telescopes
- Page ID
- 162999
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Lab Overview
Lab Goals
As a result of this lab, you should be able to:
- Describe how concave and convex lenses and mirrors affect light rays
- Identify a mathematical pattern related object distance, image distance, and focal length for a double-convex lens (thin lens/mirror equation)
- Use scale-model diagrams to explain how a simple refracting telescope uses two lenses to form an image that the eye can see.
Equipment and Setup
This lab requires the following equipment on each table.
- Pasco Optics System (or similar)
- Pasco Optics Track (or similar)
- Graph Paper
Submission Instructions
Submit a brief lab report that includes the following sections:
Results
Include all data tables and calculations. Make sure everything is properly labeled with clear and accurate units.
Discussion
Your discussion should summarize your responses to the questions throughout the lab manual. You might choose to group some questions together in this response. Each paragraph should be organized in a Claim-Evidence-Reasoning format:
- Claim: A succinct one-sentence answer to the question.
- Evidence: A sentence or two that selects and summarizes measurements, descriptions, or patterns from your lab. Be as clear as possible. You might want to add labels or color-coding to your models to make it easy to refer to specific parts or components.
- Reasoning: Explain how the specific evidence you selected supports/justifies your claim. Imagine you are explaining it to someone who is not in this lab so they do not have the background information that you have.
Part 1: Single Optic Systems
Background Information
Lens and mirror surfaces can be flat or curved with two different types of curvatures: Concave and Convex.
The material a lens is made from and the way a lens/mirror is curved will influence the way that optical component bends light. This bending of light is what allows a telescope to brighten and enlarge our view of an object.
Concave and Convex Lenses and Mirrors
Lenses
Explore how lenses affect incoming, parallel light rays and determine which type of lens converges light.
- Set up the optical track with the parallel laser emitter pointing towards higher numbers on the track.
- Position one of the free lenses (not one in a black holder) so that it is flat on the track with a curved edge facing the lasers. Draw a picture of the setup, including the beams before and after they go through the lens. Repeat for the other lenses.
Discussion Questions:
- How do the different shapes of the lenses affect the way they bend light?
- Which lens converges light to a point?
Mirrors
Explore how mirrors affect incoming, parallel light rays and determine which type of mirror converges light.
- Set up the optical track with the parallel laser emitter pointing towards higher numbers on the track.
- Position one of the free mirrors (not one in a black holder) so that it is flat on the track with a curved edge facing the lasers. Draw a picture of the setup, including the beams before and after they go through the lens. Repeat for the other mirrors.
Discussion Questions:
- How do the different shapes of the mirrors affect the way they bend light?
- Which mirror converges light to a point?
Focal Length and Image Creation
Now we will explore how lenses affect all of the light from an object by constructing the setup shown below:
- Remove the parallel laser emitter and replace it with the light source.
- Return the free lenses and take out the lenses that are in black holders. These holders allow the lenses to snap into the optical track and slide to different positions.
- Add a screen near the end of the track. You will slide this around later.
- Choose one lens that is the type that converges light and put it between the light source and the screen at a position of 30cm in front of the light source. This is called the object distance ( do ).
- Move the screen back and forth until you get a clear image on the screen. Record the distance between the lens and the screen as the image distance ( di )
- Add the two distances together (do + di) to calculate the total distance from the object to the image.
- Repeat the above steps for 4 different object distances.
|
do |
di |
do + di |
|
30 cm |
||
Discussion Questions:
- Describe any patterns you notice in your data
- When the object distance increases, does the image distance increase or decrease?
- Were there any object distances that did not form a clear image? Were they large or small distances?
Some quantities have reciprocal relationships. Calculate the reciprocals of your data and fill in the table below. Round to two decimal points.
|
1/do |
1/di |
1/do + 1/di |
|
30 cm |
||
Discussion Questions:
- Describe any patterns you notice in your data
- Try to construct an equation relating the object distance and image distance
Thin Lens/Mirror Equation
The relationship between the location of an object, a lens/mirror, and the image that is formed by that object/mirror is given by the thin lens/mirror equations:
Part 2: Primary and Secondary Optics
Background Information
Two different optical components (lenses/mirrors) can be used in combination with one another. The first component that the light interacts with is called the primary and the next is called the secondary. On the lab bench, count starting with the component that is closest to the light source (object).
Lab Instructions
Shorter Focal Length Primary and Larger Focal Length Secondary
Use the shorter focal length double convex lens as your primary lens and the larger double convex lens as your secondary lens. Start with the Primary lens 50cm from the light source (d1 = 50cm).
- Place the secondary at the end of the track and look through the secondary to see the light source on the other side of the primary lens. Make sure everything is lined up (the light source might be blurry).
- Adjust the secondary lens until the image first becomes clear. Record the distance between the primary and secondary lenses (d2).
- Move the primary to 2-3 other positions (ie, change d1) and then move the secondary to create a focused image. Record all positions.
- Use your data to create a scale model of the optical system for each position of the primary lense:
- Draw a line at the positions of the object, the Primary Lens and the Secondary Lens. Label them.
- Use the thin lens equation to identify the position of the image that is created from the primary lens (di).
- The image from the primary becomes the object for the secondary. Identify the distance between this image/object and the secondary lens (do).
- Use the thin lens equation to (try to) identify the position of the second image that is created from the secondary lens.
|
d1 |
d2 |
di |
do |
|
50 cm |
|||
Larger Focal Length Primary and Shorter Focal Length Secondary
Now switch to use the larger focal length double convex lens as your primary lens and the shorter double convex lens as your secondary lens. Start with the Primary lens 50cm from the light source (d1 = 50cm).
- Place the secondary at the end of the track and look through the secondary to see the light source on the other side of the primary lens. Make sure everything is lined up (the light source might be blurry).
- Repeat the process as before to collect data on the locations of clear images in this new configuration
|
d1 |
d2 |
di |
do |
|
50 cm |
|||
Discussion Questions
- What patterns do you notice in your tables for the two telescopes that you made?
- Where does the image formed by the primary need to be in relation to the primary/secondary lens?
- Where is the secondary image? Why is this a good location?
- If you want to make a larger image of the object compared to what you would see without a telescope, which should be bigger, the primary or the secondary?
- Summarize how a Simple Refracting Telescope works. Draw an example diagram to go along with your description that includes the primary lens, primary image, and secondary lens.