As a homework helper, I'm really not supposed to give the answer, but on this one, I will bend the rules a little, because any explanation of this leads you immediately to the answer. ## \\ ## With a prism, basically light bends as it enters the prism, and that is called refraction. The emerging angle depends on Snell's law, which contains the index of refraction ## n ## in the formula. Because the index ## n ## of refraction can be wavelength dependent, and it is for the kind of glass that is used in a prism, the different wavelengths, basically the colors of the rainbow, are bent different amounts, and the light is separated into the different colors. Alternatively, the speed of light ##v=\frac{c}{n} ##,(## c ## is the speed of light in the vacuum), is different for the different wavelengths inside a material, (since index ## n ## changes slightly with wavelength), and both the separating of the colors, and the speed of light being different for different wavelengths are known as "dispersion".
