Reflection in a convex mirror (Item No.: P )

Transcription

1 Teacher's/Lecturer's Sheet Reflection in a convex mirror (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Optik Subtopic: Reflebion und Brechung Experiment: Reflebion am Wölbspiegel Difficulty Preparation Time Execution Time Recommended Group Size Easy 10 Minutes 10 Minutes 2 Students Additional Requirements: Experiment Variations: Ruler (approb. 30 cm) White paper (DIN A4) Compasses Keywords: Task and equipment Information for teachers Additional Information The ebperiments on reflection in conveb mirrors serve to reinforce the knowledge gained in the ebperiments on plane and concave mirrors, and further to improve ebperimental proficiency. On the one hand, the goal of this ebperiment is the observation of reflection in a conveb mirror, and while doing so to ebperimentally determine the focal point and the focal length. On the other hand, by observing one selected light beam the students should be led to the realisation that the laws of reflection determined for the plane mirror are general truths; and thus can also be applied to conveb mirrors. Suggestions Similarly to the ebperiments on a concave mirror, particular attention must be paid that the students' positioning of the mirror (outer centre of curvature on the point S on the optical abis) and the light bob (incidence of the middle narrow light beam along the optical abis to check the correct positioning - "0 -method") is ebact, so that an unequivocal and convincing ebperimental result is achieved. In some cases difficulties for the students could occur due to the fact that the conveb mirror, like the plane mirror, forms virtual images; consequently, a backward ebtension of reflected light beams becomes necessary.

2 Reflection in a convex mirror (Item No.: P ) Task and equipment Task How is lixht reflected in a convex mirror? 1. Investigate the reflection of light in a conveb mirror; determine the focal point and the focal length ebperimentally. 2. Determine the angle at which a selected light beam is reflected.

3 Equipment Position No. Material Order No. Quantity 1 Light bob, halogen 12V/20 W with single-slit/double-slit aperture with triple-slit/five-slit aperture 1 4 Mirror, concave-conveb PHYWE power supply DC: V, 2 A / AC: 6 V, 12 V, 5 A Additional material Set-up and procedure 1. Reflection in a convex mirror Ruler (approb. 30 cm) 1 White paper (DIN A4) 1 Compasses 1 Prepare a sheet of paper as shown in the picture (label a point on the optical abis with "S").

4 Fig. 1 Place the conveb mirror with its centre of curvature on point S. Mount the five-slit aperture on the light bob's lens end and place it on the edge of the sheet of paper about 10 cm away from the mirror. Fig. 2 Connect the light bob to the power supply (12 V AC) and switch it on. Fig. 3 Move the light bob until the narrow central light beam of the five-slit aperture runs ebactly along the optical abis (pencil line). If you have positioned the mirror correctly, this light beam will be reflected back on itself; otherwise, rotate the mirror slightly.

5 Fig. 4 Trace the outline of the conveb mirror onto your sheet without moving the mirror. Fig. 5 What can you say about the path of the outer light beams? Note your observations. Mark all the incident and reflected light beams with two crosses (or other marks) each; use different colours for different beams. Fig. 6 Switch off the power supply and remove the light bob and the mirror from the paper. Connect the corresponding marks so that the paths of the light beams before and after reflection in the conveb mirror are visible. Ebtend the reflected light beams backwards with dashed lines through the curvature of the mirror. Label the intersection of the ebtended lines with "F". Where is the intersection located?

6 Determine the distance from point F to apeb S and note the measured value. 2. Reflection of a lixht beam in a convex mirror Prepare a second sheet of paper analogously to that used in the first part of the ebperiment. Place the conveb mirror with its outer curvature on point S. Mount the single-slit aperture on the light bob's lens end and switch on the power supply (12 V AC) again. Let the narrow light beam hit the mirror ebactly at point S at an angle. Fig. 7 Observe the light beam reflected by the conveb mirror; mark the path of the incident and the reflected rays with two crosses each. Fig. 8 Switch off the power supply and remove the light bob and the mirror from the paper. Connect the corresponding marks so that the path of the light beam before and after reflection is visible. Measure the angle of incidence (α) and the angle of reflection (β); record your results.

7 Report: Reflection in a convex mirror Result - Observations 1 (10 Punkte) What can you say about the path of the outer light beams? Note your observations. Result - Observations 2 (10 Punkte) Label the intersection of the ebtended lines with "F". Where is the intersection located? Determine the distance from point F to apeb S and note the measured value.

8 Result - Observations 3 (10 Punkte) Note your observations from the second part of the ebperiment. Evaluation - Question 1 (10 Punkte) Using your observations for the first part of the ebperiment, describe how a light beam which is incident to the conveb mirror at an angle is reflected.

9 Evaluation - Question 2 (10 Punkte) Why is a light beam which is incident along the optical abis reflected back on itself? Evaluation - Question 3 (10 Punkte) Ebamine your results for the first part of the ebperiment; where do the parallel light rays which hit the conveb mirror appear to come?

10 Evaluation - Question 4 (10 Punkte) With your compasses double the length of the line segment FS (first part of the ebperiment) along the optical abis. You obtain a further intersection M. Construct a circular arc around M with the radius MS and compare it with the outline of the conveb mirror. What do you notice? Evaluation - Question 5 (10 Punkte) From your measuring results for the angle of incidence and the angle of reflection, give reasons for the path of the light beam incident to the apeb S at an angle after reflection (second part of the ebperiment).

11 Evaluation - Question 6 (10 Punkte) List some applications for conveb mirrors.