Image construction for a convex mirror (Item No.: P )

Transcription

1 Teacher's/Lecturer's Sheet Image construction for a convex mirror (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Optik Subtopic: Reflebion und Brechung Experiment: Bildkonstruktion 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 aim of this ebperiment is the ebperimental determination of the intersection of selected light beams which hit a conveb mirror and the image construction which follows from that. In a preliminary ebperiment the characteristics of the mirror image are determined. So it is possible to compare both ebperimental results later. The ebperiment is very demanding on the students' required ebperimental proficiency and on the knowledge gained by performing it. There are no real images; the intersection of the backward ebtensions of the reflected light beams lies behind the conveb mirror. Thus, it is possible to illustrate the character of virtual images to the students and to deepen their knowledge of virtual images on plane mirrors. Suggestions Special attention should be paid that the students are very painstaking in their positioning of the mirror (centre of the conveb surface on point S on the optical abis) and the light bob (narrow light beam incident along the optical abis to test for correct positioning) so that unequivocal and convincing ebperimental results may be obtained. To facilitate the parallel shift of the light bob, a thin pencil line should be drawn parallel to the optical abis from the tip of the object arrow to the conveb mirror before beginning the ebperiment.

2 Imnge construction for n convex mirror (Item No.: P ) Tnsk nnd equipment Tnsk Why do you see yourself smnller when looking into n silver bnll? 1. Investigate the properties of a mirror image for a conveb mirror. 2. Investigate image formation in a conveb mirror using selected light beams.

3 Equipment Position No. Mnterinl Order No. Qunntity 1 Light bob, halogen 12V/20 W with single-slit/double-slit aperture 1 3 Mirror, concave-conveb PHYWE power supply DC: V, 2 A / AC: 6 V, 12 V, 5 A Additional material Set-up nnd procedure Attention! Ruler (approb. 30 cm) 1 White paper (DIN A4) 1 Compasses 1 Ensure that the centre of the conveb mirror's outer curvature always lies on point S and that its position does not change when the light bob is moved. 1. Chnrncteristics of n mirror imnge Hold the conveb mirror directly in front of you and look into it. What characteristics of your mirror image do you notice? Note your observations. 2. Imnge formntion by n convex mirror Prepare a sheet of paper as shown in the picture.

4 Fig. 1 The distances F@S@ and M@S@ are each 7.2 cm; the circle around M has the radius M@S@. Draw a 2 cm high arrow perpendicular to the optical abis 6 cm away from point S (on the side opposite from F and M); label this arrow with "G". Draw a thin guide line which touches the tip of the arrow and which is ebactly parallel to the optical abis. Mount the single-slit aperture on the light bob's lens end and place the light bob and the conveb mirror on the piece of paper (Fig. 2). Fig. 2 Connect the light bob to the power supply (12 V AC) and switch it on. Fig. 3 Check the position of the mirror by letting a narrow light beam hit the mirror along the optical abis.

5 Fig. 4 Move the light bob until the narrow light beam runs ebactly along the guide line parallel to the optical abis and just touches the tip of the arrow (imaginary object). Observe the light beam reflected by the conveb mirror and mark the path of the incident and the reflected light beam with two crosses each. Fig. 5 Turn the light bob until the light beam is pointing directly at point S but still touches the tip of the object arrow G. Again observe the light beam reflected by the mirror and mark the path of the incident and the reflected beams with two crosses each (different colour). Fig. 6 Switch off the power supply and remove the light bob and the conveb mirror from the paper. Connect the corresponding "crosses" so that the paths of the respective light beams before and after reflection in the conveb mirror become visible.

6 Ebtend the reflected light beams with dashed lines through the mirror. What do you notice? Record your observations.

7 Report: Image construction for a convex mirror Result - Observations 1 (10 Punkte) Note your observations from the first part of the ebperiment. Result - Observations 2 (10 Punkte) Note your observations from the second part of the ebperiment.

8 Evaluation - Question 1 (10 Punkte) The intersection of both ebtensions of the reflected light rays is a picture of the tip of the object arrow: Draw the perpendicular from this intersection to the optical abis; label this arrow with "B". Evaluation - Table 1 (6 Punkte) Compare this image arrow B with the object arrow G. What can you say about its size, position and distance from point S? Record your observations and measurements in the table below. Object arrow G Image arrow B Size 1 ±0 1 Orientation to the optical abis 1 1 Distance from apeb S 1 ±0 1

9 Evaluation - Question 2 (10 Punkte) Based on your observations and measurements formulate a statement which tells you the orientation, size and distance of the image compared to the object arrow. Evaluation - Question 3 (10 Punkte) Why does one see oneself reduced in size in a silver Christmas ornament?

10 Evaluation - Question 4 (10 Punkte) Draw a straight line from the tip of the object arrow to point M. What do you notice? How would a light beam which is incident to the conveb mirror along this line be reflected? Evaluation - Question 5 (10 Punkte) What is different/special about the image formed by the conveb mirror?