GET FOCUSED

During this Investigation, students will conduct two Trials. In Trial 1, students will view an object (a piece of oat cereal) with the unaided eye, a convex lens, and a convex lens in order to answer the following questions:

• How are the images produced by lenses different than the object viewed with the unassisted eye? How are they different?
• How are the images produced by concave and convex lenses different? How are they similar?

In Trial 2, students will view a microscope slide of the letter “e” in order to answer the following question:

• How are the images produced by convex and concave lenses and a microscope different? How are they similar?
• How are the images produced by a microscope similar to that of the unassisted eye? How are they different?

1. Direct each of the five student groups to obtain the following necessary materials from the distribution point: one (1) convex lens, one (1) concave lens, one (1) round oat cereal piece, one (1) metric ruler, and one (1) Letter “e” slide.

Note: If time in the lab is a concern, one student in each pair/group should be responsible for recording the required data in the Scientist Data Record. The remaining students can transfer the data into their records at the end of the experiment.

Trial 1:

Trial 1 has been designed to provide students with an opportunity to explore the refraction of light by convex and concave lenses. As students perform this trial they will observe a round oat cereal piece with the unassisted eye, a convex lens, and a concave lens. By comparing their observations of the oat cereal piece under these three conditions, students should note that the oat cereal piece appears different when viewed with the convex and concave lens than when viewed with the unassisted eye. In addition, the image of the oat cereal produced by the convex lens differs from that produced by the concave lens. Analysis of their results should lead students to infer that both the convex and concave lens refracts light because both produce an image that appears distinctly different from the object. 

Also during this Trial, students will be asked to measure the inner and outer diameter of the round oat cereal piece when viewed under all three conditions. By doing so, students will gather quantitative data about the differences in the images produced by the convex and concave lenses and the object viewed with the unassisted eye. During the Post-Lab, students will compare the ratio of the inner to the outer diameter of the oat cereal piece when viewed with the unassisted eye, the convex lens, and the concave lens. Upon comparison, students will find that the ratio remains unchanged under the three viewing conditions. This comparison will help students understand that although the refraction of light by lenses can produce images that are magnified (convex lens) or reduced in size (concave lens) when compared to the object, the proportions of the object are maintained in the image. 

KEYS: TRIAL 1

Trial 2:

As students complete Trial 2, each pair will take turns viewing the label of the Letter “e” slide at the table with the microscope, convex and concave lens. In order to assist this sharing process, suggest that each pair first view the Letter “e” slide with the unassisted eye, take the appropriate measurements and begin sketching the appearance of the word “Letter.” Four pairs of students should then concentrate on the sketch while one pair observes and obtains measurements with the convex lens. The convex lens can then be passed to another student pair while the previous pair works on the sketches of the word “Letter” with the unassisted eye and the convex lens. Once all students have completed their observations with the convex lens, the same process can be repeated for the concave lens and the microscope. Comparison of the images observed with the convex lens, concave lens, and under the 4X objective of the compound microscope should help reinforce the concepts that lenses refract light, that the refraction of light produces images that appear different from the object, and that the proportions of an object are maintained when viewing its image with lenses. In addition, this trial will provide students with an opportunity to learn the parts of the compound microscope and become familiar with its use and operation. The procedural knowledge of the microscope’s use and operation gained during this trial will be utilized by students in Investigations Two through Five as they view different microscopic specimens. 

KEYS: TRIAL 2

CLEAN UP

Let students know your expectations for clean-up. Ask them to clean up.