Complementary colours (Item No.: P )

Size: px

Start display at page:

Download "Complementary colours (Item No.: P )"

Susan Freeman
6 years ago
Views:

1 Teacher's/Lecturer's Sheet Complementary colours (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Optik Subtopic: Farbenlehre Experiment: Komplementärfarben Difficulty Preparation Time Execution Time Recommended Group Size Intermediate 10 Minutes 10 Minutes 2 Students Additional Requirements: Experiment Variations: White paper (DIN A4) Protractor Ruler (approx. 30 cm) Keywords: Task and equipment Information for teachers Additional information In this experiment, the students first review their knowledge of the dispersion of light by a prism and the reuniting of spectral colours with the aid of a converging lens. The main emphasis of the investigations is one the observation of the secondary colours that arise when individual spectral colours are blocked out of the spectrum. What should be learnt is that the secondary colour (the complementary colour) and the blocked out spectral colour, when recombined, produce white again. As a memory aid for complementary colours, a simple scheme is given which adequately fits the findings. The complete Newton colour circle and the findings of Helmholtz on complementary colours are not gone into here. This experiment is also to be seen as a foundation for the understanding of additive and subtractive colour mixing. Suggestions For this experiment, a narrow light beam which strikes the prism is required. In this way, a clear convergence point (image point) is achieved after the light passes through the prism and the lens combination so that the colours reunitr again. (The object point is the point where the white light bundle strikes the prism). The guide lines serve for adjustment in order to ebsure an experiment which is reproducible and as error free as possible. The spectrum in this arrangement is particularly widely fanned out.attention should be paid that the entire violet component emerges from the prism. The converging lens should be positioned at about 10 cm from the perpendicular line so that the spectrum is sufficiently widened to allow blocking out the spectral colours. In additon, care should be taken that the light beams passes through the middle of the lens and is symmetrical to its optical axis to prevent colour defects in the image. The observation of the convergence point is subjective and the colour impression in dependent on a good adjustment and blocking out of a spectral colour. Therefore, the paper strip is first moved sloely and continually through the spectrum abd the type of colour change observed. Then the three colours whose complementary colours are distinctly different are selectively blocked out. Remark to Result - Table 1 The blocking out of a particular colour requires great care and the subjective judgement of colour at the convergence point may differ. The students should, however, normally name one of the two colours given in Table 1.

2 Teacher's/Lecturer's Sheet

Complementary colours (Item No.: P1066300) Task and equipment Task What are complementary colours?

3 Complementary colours (Item No.: P ) Task and equipment Task What are complementary colours? Fade out individual colours of the spectrum from white light and investigate which secondary colours appear.

4 Equipment Position No. Material Order No. Quantity 1, 2 Block,planoconvex lens,fl+100mm Block, trapezoidal , 5 Light box, halogen 12V/20 W Additional material Set-up and procedure Set-up Attention! PHYWE power supply DC: V, 2 A / AC: 6 V, 12 V, 5 A White paper (DIN A4) 1 Protractor 1 Ruler (approx. 30 cm) 1 Take care that when you fade out individual colours of the spectrum using a strip of paper the positions of the white light and the block do not change. Set-up Lay a sheet of paper crosswise in front of you on the table. In the left-hand corner draw right-angled, crossed lines and labe the intesection M. At a distance of 1 cm below and 5 cm above M, make two marks on the perpendicular line. Starting at M, measure an angle of 28 and draw a guide line.

Fig. 1 Place the trapezoidal block between the two marks on the

Fig. 2 Cut out a small strip of paper about 1 mm wide and lay

5 Fig. 1 Place the trapezoidal block between the two marks on the perpendicular line. Insert the single-slit into the lens end of the light box and position this at the edge of the sheet as shown in the picture. Fig. 2 Cut out a small strip of paper about 1 mm wide and lay this on the side for later use. Fig. 3 Procedure Connect the light box to the power supply (12 V AC) and switch it on.

$Observe the refracted light beams that leave the prism.$ $The position of the light box is correct when the refracted light beam appears totally coloured and the violet component is$ This lens combination should be about 10 cm from the perpendicular line.

This lens combination should be about 10 cm from the perpendicular line.

6 Fig. 4 Let the light beam exactly fall exactly along the guide-line on the prism. Observe the refracted light beams that leave the prism. The position of the light box is correct when the refracted light beam appears totally coloured and the violet component is visible. Fig. 5 Bring the two juxtaposed convex lenses into the coloured fanned-out light beams. This lens combination should be about 10 cm from the perpendicular line. Take care that the light beam travels as closely as possible through the middle of the lens. Describe the path of the light beam and the colours seen following passage through lenses. Fig. 6 Move the narrow strip of paper in front of the lenses throught the coloured light blocking out eveatually each individual

7 colour, one by one. Begin with the red "outer" part of the light beams and move the strip slowly towards the violet edge. Observe narrowest point of the light beams (convergence point) behind the lens and note the change. Now selectively fade out the colours red, green and blue and note the corresponding colour at the point of convergence. Fig. 7 Switch off the power supply and remove the light box and the blocks from the paper.

8 Report: Complementary colours Result - Observations 1 (10 Punkte) Note your observations on the colours in the lioht beams after passino throuoh lens combination. the chanoes in colour at the converoence point when the colours from red to violet are blocked out, one after another, with a narrow strip of paper. Result - Table 1 (3 Punkte) Note your observations in the table. Blocked out spectral colour Colour at the convergence point Red 1 Green 1 Blue 1

9 Evaluation - Question 1 (10 Punkte) Give an explanation for the observed colour of the light beams at the convergence point of the lens combination when no colour is blocked out. Evaluation - Question 2 (10 Punkte) How does the colour at the convergence point change when a colour of the spectrum is blocked out?

10 Evaluation - Question 3 (10 Punkte) The blocked-out spectral colour and colour visible the colour at the convergence point are called complementary colours. Decide which colour would be produced when two complementary colours overlap. Evaluation - Table 1 (6 Punkte) Write the complementary colours to those mentioned in the table. Spectral colour Complementary colours Red 1 Orange 1 Yellow 1 Green 1 Blue 1 Violet 1

Colour dispersion with a prism (Item No.: P )

Teacher's/Lecturer's Sheet Colour dispersion with a prism (Item No.: P1066100) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Optik Subtopic: Farbenlehre Experiment: