30 Jun, 2013
With a prism
PRESENTATION: In optics, a prism is an object that is capable of refracting, reflecting and breaking light up into the colours of the rainbow. Generally, such objects take the form of a triangular prism, hence the name. The first person to study this phenomenon was the Frenchman René Descartes, who explained the formation of the rainbow in 1637, although it was not until 1671 that Sir Isaac Newton managed to break white light up using a prism and observed that it was formed by a band of colours (red, orange, yellow, green, blue, indigo and violet).
- Why is white light dispersed by a prism?, Frank S. Crawford, Phys. Teach. 17, 583 (1979)
INTRODUCTION: Newton worked to a great extent on the problems that existed in optics and the nature of light. By projecting white light, he demonstrated that it was made up of a band of colours (red, orange, yellow, green, blue, indigo and violet). His experiments on the nature of light led him to formulate his general theory to explain that light is composed of corpuscles (particles). Nowadays, scientists have come to the conclusion that light has a dual nature: made up of waves and corpuscles at the same time. The phenomenon of light dispersion can be observed in Nature, when standing between the Sun and an area where it is raining. This is when a rainbow can be seen.
OBJECTIVE: To demonstrate that white light is made up of a series of colours, each of which is characterised by a specific wavelength.
MATERIALS: Halogen lamp (12V, 20W), alternating current power source, different types of prisms and lenses, cables.
SETUP: The bulb is fixed in the lamp holder in such a way that the thin rectangular beam we will need is projected onto the surface of the prism. The position of the prism should be altered so that in one specific position the light is broken up into colours. The surface on which the experiment is done should preferably be white so that the colours stand out.
EXPLANATION: The law of refraction indicates that if lights that are incident on a surface have different wavelengths, then they will be refracted at different angles. This is because light, when it is incident on the surface of another material, reduces its velocity compared to that in a vacuum. The relationship between both velocities is the refractive index, which depends on the properties of the material and the wavelength of the light. White light is actually a mixture of all the electromagnetic waves in the visible spectrum, all with different wavelengths, each of which corresponds to a colour (going from red to violet), which means that each colour is refracted at a different angle. A prism can be used to boost the effect because it increases the separation at the second refraction. The colours that make up white light can then be identified in an organised way. The shift from their original path is progressive, with larger frequencies (or smaller wavelengths) shifting more, so that seven colours can be seen: violet, indigo, blue, green, yellow, orange and red, as well as ultraviolet and infra-red at each end of the spectrum, which cannot be seen by the human eye but can form an image on photographic plates.
CONCEPTS: refractive index, prism, wavelength.
- GALERIA DEL PROYECTO
- YOUTUBE 1
- YOUTUBE 2
- PHYSLET 1
- PHYSLET 2
- WAKE FOREST UNIVERSITY
- Tipler P.A. Física, Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A, Jewett J.W., Física, Thomson-Paraninfo, 2010.
STUDENTS 2012-2013: Rodrigo Graña, Xeila Iglesias, Samuel Carballo, José M. Campos.
LINK pdf STUDENTS (in Spanish):
STUDENTS 2012-2013: Antonio Sixto, David Zúñiga.
LINK pdf STUDENTS (in Spanish):