Light path of lens combinations (Item No.: P )

Transcription

1 Teacher's/Lecturer's Sheet Light path of lens combinations (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Optik Subtopic: Linsengesetze Experiment: Strahlengang bei Linsenkombinationen Difficulty Preparation Time Execution Time Recommended Group Size Easy 10 Minutes 10 Minutes 2 Students Additional Requirements: Experiment Variations: White paper (DIN A4) Ruler (approx. 30 cm) Keywords: Task and equipment Information for teachers Additional information In the experiments concerning combinations of lenses, the students' understanding of the light path through convex and concave lenses is both strengthened and extended. The first experiments serve as direct revisions, the experiments involving the combination of a planoconcave lens with a biconvex lens provide the opportunity for the students to understand that by using particular combinations of lenses and changing their distance of separetion, different total focal lengths can be achieved. At the same time, however, only qualitative statements are strived for. Since the results obtained with a combination of a planoconvex lens with a planoconcave lens of the same curvature leads to a surprising result as far as the students are concerned, it offers a good starting point for a revision of the law of refraction. The experiment is not so demanding in terms of the abilities and experimental skills required of the students. lowever, skills related to the careful adjustment of the experimental setup can be further developed. These are immediate prerequisites for the quantitative determination of focal length for lens combinations. Suggestions The precise adjustment of the respective positions of the blocks, in particular the juxtaposed planoconvex lenses, with the help of the middle incident beams along the optical axis is necessary in order to obtain convincing, experimental results. Using the semicircular, convex lens contained in the set of apparatus, and by changing the sequence of lenses used, it is possible to assemble still more lens combinations which can be investigated experimentally.

2 Light path of lens combinations (Item No.: P ) Task and equipment Task How does light travel through lens combinations? Investigate the course of light passing through a combination of convex and concave lenses.

3 Equipment Position No. Material Order No. Quantity 1, 2.lock,planoconvex lens,fl+100mm lock, planoconcave lens,fl-100mm , 5 Light box, halogen 12V/20 W Additional material PHYWE power supply DC: V, 2 A / AC: 6 V, 12 V, 5 A White paper (DIN A4) 1 Ruler (approx. 30 cm) 1

4 Set-up and procedure Set-up Attention! Take care that the lenses lie with their flat sides precisely on the perpendicular of the crossed lines and that their position does not change during the experiment. Set-up Draw crossed lines at right angle to each other in the middle of your sheet of paper. The intersection of the lines is point M. Make two marks, one on either side of M, at a distance of 3 cm away from M. Fig. 1 Lay the planoconvex lens (rough side downwards) with the flat side precisely on the perpendicular line within the two marks. Insert the three-slit aperture in the light box on the lens side and position this about 10 cm from the plane edge of the block. Fig. 2 Procedure Connect the light box to the power supply (12 V AC).

5 Fig. 3 Move the light box and, if necessary, the lens carefully until the middle light beam travels precisely along the optical axis and on passing the lens is not refracted. Observe the course of the parallel light beams on passing through the lens and note your observations in the table in the report. Mark the position of the focal point on the optical axis. Fig. 4 Change the experimental setup step by step as illustrated. In each case observe the path of the light and, in particular, the position of the focal point. Note all observations in the table in the report.

6 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Switch off the power supply and remove the light box and the block from the paper.

7 Report: Light path of lens combinations Result - Table 1 Note your observations in the table. Lense in light path Observation on the path of the light beams Position of the focal po Evaluation - Question 1 What difference exists between a planoconvex lens and a planoconcave lens in terms of the refraction of parallel, incident light?

8 Evaluation - Question 2 Which changes results in the light path when a planoconvex lens is transferred into a biconvex lens? Evaluation - Question 3 How can the focal length be changed?

9 Evaluation - Question 4 What is the effect of the combination of a planoconcave lens and a planoconvex lens having the same curvature? Explain this. Evaluation - Question 5 Where are combinations of lens used? Give two examples.