Free Download of Jamb (UTME) Physics past questions with Answers on 'Colours of Light.'
There have been lots of posts out there stating 'Free Download of UTME Physics past questions with Answers' but only questions without answers. This has prompted me to painstakingly create this pack by solving Jamb physics past questions on different topics and making them available for download free. Not only are these questions solved topics by topics, they're also solved systematically from the simplest to the hardest. It is a unique past questions pack with answers to make easy the studying of this subject. Colours of Light is one of the most elusive topics in physics and it is presented in a coherent and concise form in Jamb past questions with answers by SB Sanni of Babatunde Elucidation.
Side Note: 'ume 91@04' in the pack implies ume 1991 question number 4.
As the description of the website displays-understanding what you know is the key-I would like to explain briefly on this topic.
Brief explanation on the topic
Colours in white light
The above figure depicts the experiment carried out by Sir Isaac Newton in Cambridge in 1666. He made a small circular opening in a shutter in a darkened room and placed a prism near the hole, so that the light was refracted on to the opposite wall. The colours produced in this way were, in order from the apex side A of the prism
Red, orange, yellow, green, blue, indigo, violet (ROYGBIV)
These colours are called the spectrum of white light. Our natural white light comes from the sun. The beautiful colours in the rainbow are due to dispersion of sunlight by water droplets suspended in the air after rain has occurred. A similar colour effect is produced by drops of water from a garden hose when sunlight is present.
Dispersion and recombination with prism
Newton began a series of experiments to find out whether colours were already in white light, or whether colour was somehow added to it by the prism.
Like in his first experiment, another 60° glass prism Y is now placed to intercept the coloured beam before it reaches the screen as shown in the figure (a) above. On moving S round, the colours are now seen to be more widely separated than before, but are still ROYGBIV. so prism Y does not create colours. The prism Y is now turned round so that its 60° angle points the other way to that of the prism X and the sides of the prisms are parallel-fig (b). When the screen S is moved the image on S is seen to be white. The prism Y has now neutralised the colour effect produced by X.
Newton therefore concluded that the colours were present in white light. The glass prism X simply separates them; they travel in different directions in glass. We say that a glass prism produces dispersion of the colours in white light. In fig. (a) above, the second prism, Y, helps to produce greater dispersion. Dispersion is due to the different speeds that the coloured rays move in glass. Each colour in a ray of white light is then refracted in a slightly different direction on entering a glass prism. Since red is deviated least from its original direction in air, its change of speed on entering glass is least. Hence red light travels in glass with the greatest speed. As violet light is deviated most on entering the glass, it has the slowest speed in glass. In a vacuum, all colours travel with the same speed.
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