Dispersion is the splitting of white light into its colour components.

Transcription

1 Chapter 21 Clurs (A) Dispersin 1. Define dispersin. Dispersin is the splitting f white light int its clur cmpnents. 2. What is the clur that sunlight appears t be? White 3. State the seven clurs in sunlight / white light. Red Orange Yellw Green Blue Indig Vilet Memry Help (just remember ne f the fllwing sentences): Richard f Yrk gains battle in vain Ry gives birth in Vietnam Cmment: The exact sequence is imprtant and must be fllwed. I.e. yu must give red first, fllwed by range, then yellw and finally vilet. 4. Describe hw the dispersin f sunlight results in a rainbw. When sunlight enters water drplets in air, the different clur cmpnents f white light slw dwn by different amunts. As a result, the seven different clurs bend twards the nrmal thrugh different angles. On leaving the drplet, the separated clurs will bend again but nw away frm the nrmal t prduce the rainbw clurs. 5. State whether red r vilet light bends the mst when made t underg refractin. Vilet. Memry Help: V fr victry. Hence, vilet light bends the mst. Cmment: The reasn fr the bending f white light is that its seven cmpnent clurs each has a different wavelength. Red light has the lngest wavelength, while vilet has the shrtest wavelength. As such, the speed f light is slwest fr red light, and fastest fr vilet. This results in the smallest angle f refractin fr red light, and largest angle f refractin fr vilet.

2 6. Draw a diagram t shw: (a) The dispersin f white light by a prism, (b) The cmbining f the different clurs f a spectrum by tw inverted prisms. Cmments: If yu pass white light thrugh ne prism, yu will see the seven clurs f the spectrum. If, hwever, yu use tw prisms, the spectrum will merge t prduce white light again. Nte that there will be a spectrum at pint X in the diagram abve. The spectrum will recmbine t frm white light after passing thrugh the secnd prism. 7. Other than using tw inverted prisms, state anther way f cmbining the different clurs f a spectrum. Spinning Newtn s disc (this disc cnsists f the seven rainbw clurs). When the disc is spinning very fast, all seven clurs will cmbine t frm white light.

3 (B) Primary and Secndary Clurs 8. State the three primary clurs. Red Blue Green 9. What clured light is prduced when the three primary clurs are mixed in equal prprtin? White light Cmment: Thus, we can btain white light by either mixing the seven rainbw clurs, r by simply mixing the three primary clurs. 10. State the three secndary clurs. Magenta Cyan Yellw 11. Secndary clurs are prduced by mixing any tw f the three primary clurs. State the clurs that must be mixed t prduce: (a) Magenta Red and blue (b) Cyan Blue and green (c) Yellw Green and red Memry Help: Try t think f a stry t memrise the abve clur changes. Fr example, cnsider the fllwing sentence: Red is strnger than Blue, and Blue is strnger than Green. Since red is strnger than blue, it will prduce a pinkish clur f magenta (clse t red clur) when the tw clurs are mixed. Since blue is strnger than green, it will prduce a light-bluish clur f cyan (clse t blue clur) when the tw clurs are mixed Hence, the remaining clur yellw must be prduced by mixing red and green.

4 (C) Seeing Clurs 12. Fill in the blanks: We see bjects because they r light int ur eyes. This in turn depends n whether the bjects are r. emit reflect luminus nn-luminus (C1) Luminus Vs Nn-luminus Objects 13. Explain the difference between luminus and nn-luminus bjects. Luminus bjects emit light. In cntrast, nn-luminus bjects reflect light (i.e. they d nt emit light.) Cmment: Luminus bjects glw in the dark, but nt nn-luminus bjects. This is because luminus bjects generate light themselves. 14. Give three examples each f: (a) Luminus bjects Fire Lamp Sun (b) Nn-luminus bjects Chair Pencil Mn 15. What factr determines the clur that the fllwing types f bjects appear in: (a) Luminus bjects The clur f luminus bjects depends n the clur that the luminus bject emits. (b) Nn-luminus bjects The clur f nn-luminus bjects depends n the clur that the nn-luminus bjects absrb and then reflect.

5 (C2) Clur f Objects Cmments: The clur f luminus bjects is straightfrward their clurs are simply the clurs that they give ut. E.g. a luminus light-stick is green in clur because it gives ff green light. The cncept n the clur f nn-luminus bjects is slightly mre difficult t understand. We will lk int this thrugh the fllwing example. 16. State (and explain yur answer) the clur f the fllwing clured shirts under the different lighting indicated belw: (a) White light: Because the red shirt reflects the red clur in white light and absrbs all the ther clurs. (ii) Green shirt Green. Because the green shirt reflects the green clur in white light and absrbs all the ther clurs. (iii) Yellw shirt Yellw. Because the yellw shirt reflects the red and green clurs in white light, and absrbs all the ther clurs. The red and green clurs reflected appear as yellw t ur eyes. (iv) White shirt White. Because the white shirt reflects all seven clurs in white light. (b) Red light: Because the red shirt reflects the red light.

6 (ii) Green shirt Because the green shirt des nt reflect any light after absrbing the red light. Cmment: The green shirt can nly reflect green light. Hwever, the nly clured light available is red. Thus, n light will be reflected, and the green shirt appears as black. (iii) Yellw shirt Because the yellw shirt reflects the red light. Cmment: Yellw is made up f red and green clurs. Thus, the yellw shirt can reflect bth red and green light. Hwever, the nly clured light available here is red. Hence, it will reflect nly red light. (iv) White shirt Because the red shirt reflects the red light. Cmment: White is made up f seven clurs. Thus, the white shirt can reflect all seven clurs. Hwever, the nly clured light available here is red. Hence, it will reflect nly red light. (c) Blue light: Because the red shirt des nt reflect any light after absrbing the blue light. (ii) Green shirt Because the green shirt des nt reflect any light after absrbing the blue light. (iii) Yellw shirt Because the yellw shirt des nt reflect any light after absrbing the blue light.

7 (iv) White shirt Blue. Because the white shirt reflects the blue light. (d) Cyan light: Because the red shirt des nt reflect any light after absrbing the cyan light. Cmment: The red shirt can nly reflect red light. Hwever, the nly clured light available in cyan are blue and green. Thus, n light will be reflected, and the red shirt appears as black. (ii) Green shirt Green. Because the green shirt reflects the green clur in cyan light and absrbs the blue clur. Cmment: The green shirt can nly reflect green light. Cyan light cnsists f tw clurs green and blue. Thus, green light will be reflected, and the green shirt appears as green. (iii) Yellw shirt Green. Because the yellw shirt reflects the green clur in cyan light and absrbs the blue clur. Cmment: The yellw shirt can reflect bth red and green light. Cyan light cnsists f tw clurs green and blue. Since green is the cmmn light, the yellw shirt will reflect the green clur and absrb the blue clur. (iv) White shirt Cyan. Because the white shirt reflects the cyan light. Cmment: White is made up f seven clurs. Thus, the white shirt can reflect all seven clurs. Hwever, the nly clured light available here are green and blue. Hence, it will reflect bth green and blue light, and appear as cyan.