Applied Science - Technology (5B)

  • Analyzing how objects can be focused.
  • Comparing focal distances amongst classmates.


  • focal point
  • focal distance
  • optics

Students determine focal distances.


The study of lenses and light is called optics. Students will discover how images can be controlled by lenses to help observe small things. A microscope uses the physics of optics to allow us to see small things our eyes cannot detect. The principles of optics of the Swift GH microscope are the same as those in more complex microscopes. This activity has students discover how far an object must be from the objective. They will learn that this distance for the Swift GH, with a 2.5X objective and 10X eyepiece is 5.5 cm and is constant for all objects.

The focal length or focal distance is the distance between the center of a converging thin lens and the point at which parallel rays of incident light converge; or the distance between the center of a diverging lens and the point from which parallel rays of light appear to diverge. The point at which it intersects the focal plane is called the "focal point." The distance from the lens to the image is called the "optical element-image distance."


  1.  In exercise 1 on the lab sheet, students will find the optical element-distance image. Give each student a biconvex lens and an index card. Have the students create an inverted image on the card by focusing on an object. It will work much better if students stand by a window. See figure which traces the movement of the light. Students should measure the distance between the lens and the placement of the image in focus. All students should come up with the same answer (5.5 cm) if you purchased the lenses from the Math/Science Nucleus..

  1. In exercise 2, students work as partners with a Swift GH. Have each partner determine the distance where an object is in focus using different specimens. Have students measure the distance from the top of the specimen to the objective. The reason for this exercise is to learn the approximate distance from the objective to a specimen, in order for the object to be to be in focus. Provide students with objects like a small block, clothes pin, or other small objects with flat surfaces. Have students record the information on the lab sheet. Compare their information with 2 other groups and determine if the distance is the same for each object.

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