Refraction, Exams of Law

Download Refraction and more Exams Law in PDF only on Docsity! Day #1 - Refraction Let’s briefly review what we know about light. First and foremost, light travels as an electromagnetic wave. Secondly, whether we are talking about Radio waves, microwaves, ultraviolet, waves, or the visible light spectrum ROYGBIV, they are all light. Therefore, some light has a higher frequency than other light (gamma vs. radio for example) and some light has a longer wavelength than other light (infrared vs. ultraviolet, for example). Thirdly, and most importantly, we learned that all light travels at the same speed when it travels through a vacuum. This speed is 300,000,000 m/s, or 3 x 108 m/s. Since a vacuum consists of “nothingness”, there is nothing to slow light down, and it moves its fastest in a vacuum. Now for our current chapter. When light passes from one medium (or substance) into another, it changes direction. This is known as Refraction. Some materials are optically “denser” than others. For example, air is less optically dense than glass, which is less optically dense than diamond. This term, “Optically Dense” is used to refer to a medium in which the speed of light changes. For example, since a vacuum is not “optically dense” at all, light travels very fast through it. However, when light travels through diamond, which is much more “optically dense”, it will slow down. When a light ray slows down, it bends. If you look at the first picture below, it shows incident light striking a glass surface. Notice that some of the light was reflected (following the law of reflection, that says that the two angles are the same). However, some of the incident light travelled through the glass. Since it was travelling in air, and now it’s travelling in glass, the light slowed down. This caused the light ray to bend (or refract). Now look at the second picture, which shows light travelling through glass into water. Water is less “optically dense” than glass. Therefore, the speed of the light changes, and the light refracts (or bends). However, since it speeds up, it bent the other way. Lenses and the “Bending” of Light LHT Incident ray Reflected ray Refracted ray air glass Incident ray Reflected ray Refracted ray HLA glass water What does “LHT” mean? Its an easy way to remember which way the light bends when it enters a new medium (or substance). If the light travels FROM a lite (intentionally speeled wrong to avoid confusing it with the word “light”) medium INTO a heavy medium (in other words, from less dense to more dense), then the light bends TOWARDS the normal. Hence Lite into Heavy bends Towards the normal (LHT) On the other hand, if light travels FROM a heavy (or dense) medium INTO a lite (or less dense) medium, then light bends AWAY from the normal. Hence Heavy into Lite bends Away from the normal (HLA) So…..the question should be, “What makes something more or less optically dense than something else”. We measure a medium’s optical density using a ratio known as the INDEX of REFRACTION, or “n”. It is the ratio of the speed of light in a vacuum (again, 3 x 108 m/s) to the speed of light in a given material. Thus, the index of refraction is given by If you look at the table at the right, you will see the index of refraction for some common substances. The larger the index, the more light is slowed down, and thus the more it is bent. This can be seen on the following pictures… Just a reminder, since all of the pictures above show that light travels from a vacuum (less dense, Lite) into something else (more dense, or Heavy), the light bends Towards the normal. Hence LHT. On the other hand, the refracted light would have bent AWY FROM the normal if the incident light travelled from heavy into lite (hence, HLA). Medium Index of Refraction vacuum 1.00 air water 1.003 1.33 ethanol 1.36 fluorite 1.43 polystyrene 1.49 crown glass 1.52 quartz 1.54 Zircon 1.92 diamond 2.42 (where c is the speed of light in a vacuum and v is the speed of light in the new material) vacuum quartz vacuum air vacuum water