Introduction
What is the speed of light and what affects? This question has been asked for hundreds of years and the answer is simple. The speed of light is approximately 299,792,458 m/s (Las Cumbres Observatory, 2019). This answers the first part of the question, but what about the second part? What affects the speed of light? The purpose of this experiment is going to be answering that question “What affects the speed of light?”. And in particular, does the density of a substance affect the speed at which light travels through it? The researcher believes that the greater the density of a substance the slower light will travel through that substance because the density of substance greatly obstructs the straight line of light that is traveling through the substance. The researcher chose to research this topic because the speed of light is a fascinating thing that can always be explored further. This research is important because the speed of light is a very important part of learning about the universe, and by knowing how fast light travels through different substances scientists can accurately measure how far particular objects in the universe are from the earth. By doing this experiment the researcher hopes to achieve a greater knowledge of the speed of light and what affects it. The researcher also hopes to gain information in this experiment that is helpful to people who research this topic in the future. Ultimately, the outcome of this experiment should provide a clear answer as to whether density has a major effect on the speed of light in a substance or not.
Materials and Methods
Results
Discussion
The speed of light is defined as the speed at which light is transmitted in a vacuum (“Speed of Light,” n.d.). The speed of light has been measured many times since the early 1600s and continues to be refined today. The first person to try to measure the speed of light was Galileo Galilei, and he tried to do this using his pulse as a timer (Las Cumbres Observatory, 2019). This did not work as light travels much too fast for this method. In 1676 a Danish astronomer named Ole Romer was studying the orbits of the moons of Jupiter and making tables to predict when eclipses of the moons would occur (Las Cumbres Observatory, 2019). He noticed that when Jupiter and Earth are far apart the eclipses of the moons happen much later than when Jupiter and Earth are closer. He reasoned that this could be because of the time light takes to travel from Jupiter to Earth. Romer found the maximum variation in the timing of these eclipses was 16.6 minutes and interpreted this as the amount of time it takes light to travel across Earth's orbit, which would be equivalent to 301,204.8 km/s, just above the actual speed of light (Las Cumbres Observatory, 2019). In the 1850s a French physicist named Jean Foucault measured the speed of light in a laboratory using a light source, a rapidly rotating mirror, and a stationary mirror creating a much more accurate measurement of the speed of light (Las Cumbres Observatory, 2019). In the 1970s the speed of light was measured using interferometry, and then in 1983, the speed of light was measured as 299,792,458 m/s (Las Cumbres Observatory, 2019).
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When light traveling in a vacuum enters a new medium the speed is reduced. Light traveling in a uniform substance travels in a straight line at a relatively constant speed, unless it is obstructed in some manner (Parry-Hill & Davidson, 2018). When light traveling through the air enters a different medium the speed and wavelength of the light are reduced, but the frequency of the light remains unaltered (Parry-Hill, & Davidson, 2018). Light travels at 299,792,458 m/s in a vacuum, but it slows down to 225,000,000 m/s in water and 200,000,000 m/s in glass (Parry-Hill, & Davidson, 2018). In diamond, the speed of light is reduced to 125,000,00 m/s, which is about 60 percent less than its maximum speed in a vacuum (Parry-Hill, & Davidson, 2018). This means that although the speed of light in a vacuum is 299,792,458 m/s, the speed of light in other substances not in a vacuum depends on how much that substance obstructs the path of light. A useful tool that is often used to measure the distance from one point to another using the speed of light is a laser.
A laser produces a very narrow beam of light that is useful in many technologies and instruments (NASA Space Place, 2019). Laser is an acronym and it stands for light amplification by stimulated emission of radiation (Lawrence Livermore National Laboratory, n/a). “A laser is created when the electrons in atoms in special glasses, crystals, or gases absorb energy from an electrical current or another laser and become “excited.” The excited electrons move from a lower-energy orbit to a higher-energy orbit around the atom’s nucleus. When they return to their normal or “ground” state, the electrons emit photons”(Lawrence Livermore National Laboratory, n/a, How a laser works section, paragraph 1). The first laser was constructed on May 16, 1960 by Theodore H. Maiman, a physicist at Hughes Research Laboratories in Malibu, California (Rose & Hogan, 2019). Then, in December of the same year, the first laser to generate a continuous beam was developed and just a few months later lasers were available for purchase (Rose & Hogan, 2019). The first lasers were just the beginning as newer and more improved lasers are constantly being made. Lasers are different from a normal light as their light waves travel together with their peaks all lined up in a phase (NASA Space Place, 2019). They also have beams that are very narrow, very bright, and can be focused into a very tiny spot, which is different from normal light beams that tend to spread out (NASA Space Place, 2019).
Lasers are used in a variety of ways. They are used in precision tools and can cut through diamonds or thick metal, and they can also be designed to help in delicate surgeries (NASA Space Place, 2019). Lasers can also be used for recording and retrieving information. They are used in communications and in carrying TV and internet signals, and they are also found in laser printers, bar code scanners, and DVD players (NASA Space Place, 2019). They are also used when making parts for computers and other electronics (NASA Space Place, 2019). Lasers are also used in instruments called spectrometers, which help scientists figure out what things are made of (NASA Space Place, 2019). Lasers are also used in missions in space that study the gases in Earth’s atmosphere and are also used in instruments that map the surfaces of planets, moons, and asteroids (NASA Space Place, 2019). Lasers can be tiny pieces of microchips or as big as the National Ignition Facility (NIF), which is ten stories high and as wide as three football fields (Lawrence Livermore National Laboratory, n/a). Early lasers could have peak powers of maybe 10,000 watts. Modern lasers can now produce pulses that are billions of times more powerful than the early lasers (Lawrence Livermore National Laboratory, n/a). Scientists have even demonstrated NIF’s ability to generate more than 500 trillion watts of power (Lawrence Livermore National Laboratory, n/a). The length of pulses in lasers varies. Some lasers, such as ruby lasers, emit short pulses of light. Others, like helium-neon gas lasers or liquid dye lasers, emit light that is continuous. NIF, which is like the ruby laser, emits pulses of light lasting only billionths of a second (Lawrence Livermore National Laboratory, n/a). Lasers are often used when measuring the speed at which light travels through something.
Lasers have been used in the past to measure the speed light travels through a substance. The substance gelatin is different from most substances because it doesn’t confine to the normal properties of a substance. Gelatin is a protein that is made up of collagen in animal tissue and is actually the only protein with the power to thicken liquids (Joachim & Schloss, n/a). Collagen is a protein that connects muscles, bones, and skin in animals (De Pietro, 2019). When collagen is processed, it becomes a flavorless and colorless substance that is gelatin, and after the gelatin cools, it has a very jelly-like texture (De Pietro, 2019). The difference between collagen and gelatin is that gelatin dissolves in hot water, while collagen does not (De Pietro, 2019). Gelatin usually is made from the skin of a pig, which usually contains around 30% collagen by weight (Joachim & Schloss, n/a). To make gelatin, the skin of the pig is soaked in acid for around 24 hours, during this time the crosslinking proteins in the collagen unravel (Joachim & Schloss, n/a). The free protein chains that result are extracted, filtered, purified, and dried into sheets or granules that are about 90% gelatin, 8% water, and around 2% salts and glucose (Joachim & Schloss, n/a).
Gelatin is different from most other food proteins. Usually, when food proteins are exposed to heat the respond by unraveling and then they bond one another and coagulate into a firm and solid mass (Joachim & Schloss, n/a). But the proteins in gelatin don’t readily form bonds with one another (Joachim & Schloss, n/a). When the proteins in gelatin are exposed to heat it causes them to unravel and disperse just like any other protein (Joachim & Schloss, n/a). However, the proteins in gelatin never actually form new bonds, so the liquid in which they are dispersed actually stays fluid (Joachim & Schloss, n/a). Because the proteins in gelatin are so long and stringy, they often become interwoven and this causes the hot liquid that the proteins are suspended to thicken, but not actually completely solidify when warm (Joachim & Schloss, n/a). When gelatin cools, the protein strands usually line up next to one another and twist into long ropes, causing the liquid to transform into a firm gel (Joachim & Schloss, n/a).
Due to the fact that the density of gelatin can be manipulated easily, it makes it a perfect substance to see if the density of a substance affects the speed at which light travels through it. This can be tested ideally by using a laser with a continuous beam due to the fact that it gives off a beam of light that shines in a straight line and does not spread out much (NASA Space Place, 2019). Ultimately, the outcome of the experiment should give a clear answer as to whether density affects the speed at which light travels through a substance.
Conclusion
References
- De Pietro, M. (August 27, 2019). Eight health benefits of gelatin. Medical News Today. Retrieved October 18, 2019. Retrieved from https://www.medicalnewstoday.com/articles/319124.php
- Joachim, D & Schloss, A. (n/a). The science of gelatin. Retrieved October 28, 2019. Retrieved from https://www.finecooking.com/article/the-science-of-gelatin
- Las Cumbres Observatory. (2019). The speed of light. Retrieved October 18, 2019. Retrieved from https://lco.global/spacebook/light/speed-light/
- Lawrence Livermore National Laboratory. (n/a). How lasers work. Retrieved October 17, 2019. Retrieved from https://lasers.llnl.gov/education/how_lasers_work
- NASA Space Place. (June 28, 2019). What is a laser?. Retrieved October 17, 2019. Retrieved from https://spaceplace.nasa.gov/laser/en/
- Parry-Hill, M & Davidson, M. (September 10, 2018). Molecular Expressions: Speed of light in transparent materials. Retrieved October 14, 2019. Retrieved from https://micro.magnet.fsu.edu/primer/java/speedoflight/index.html
- Rose, M & Hogan, H. (2019). A history of lasers: 1960 - 2019. Retrieved October 25, 2019. Retrieved from https://www.photonics.com/Articles/A_History_of_the_Laser_1960_-_2019/a42279
- Speed of Light. (n/a). COSMOS - the SAO Encyclopedia of Astronomy. Retrieved October 15, 2019. Retrieved from http://astronomy.swin.edu.au/cosmos/S/Speed+Of+Light
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