Physics of Light and Sound (Group Journal) PDF

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It's a group assignment where you journalize the experiments that you should conduct as well as small research on each of the phenomenons that you observe....

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LSO 329 Group Assignment Physics Journal (1-4) Team members: ______

Date: _______ Subject: Exploring the Physics of Light and Sound Teacher: ______

Lab Journal 1 (12%):

Exploring the Wave Nature of Light

In Lab Journal 1 you will review the ideas introduced throughout the centuries to explain observed light phenomena. You will analyze the reasons for suggesting each model and the ways to test it. You will perform interactive numerical experiments and observations and analyze them. You will also discuss practical applications of the observed phenomena.

Part 1. Development of models about the nature of light (20 pts.) What is the nature of light? Is it rays, waves, or particles? Light is a transverse, electromagnetic wave and has a dual nature of wave and particle properties. Wave attributes of light cause interference and diffraction to happen; its transverse character causes polarization Write a brief review of the development of models of light from Antiquity to Modern Times. In your work, consider the contributions of at least 4 researchers and explain the reasons (observations and/or experiments) for suggesting the models. One of the earliest ideas that greatly advanced our knowledge of the nature of light came from al-Haytham, around 1000 AD (O'Connor & Robertson, 2002). The earlier theories of how we see things had been developed around the idea that the eyes emanate light beams onto objects –which allows us to see them (O'Connor & Robertson, 2002). al-Haytham refuted this idea by conducting a brilliant experiment; he built a pinhole camera (or camera obscura). When light passes through the narrow pinhole, an inverted image can be seen on a screen (O'Connor & Robertson, 2002). The next important discovery about the nature of light and how we are able to see was made at the beginning of the 17th century by Johannes Kepler (Finger, 2001). Kepler used a mathematical model approach to studying light; his work resulted in the correct mathematical model on how the pinhole camera works, as well as the important discovery that the human eye creates an inverted image on the retina (which he regarded as an unimportant discovery, irrelevant to his optics studies) (Finger, 2001).

Another very important discovery which further advanced our knowledge on the nature of light came from Newton, at the end of the 17th century (O'Connor & Robertson, 2002). Newton was a believer in the theory that light is composed of particles. In order to test his theory, he let a beam of white light pass through a glass prism – which resulted in the light beam splitting into its components colours. This phenomenon was attributed to the nature of the glass itself, however, Newton allowed the split-up beam of light to pass through a second inverted glass prism, which resulted in a white beam of light at the other end (O'Connor & Robertson, 2002). This experiment showed that white light is composed of many different colours; a discovery which led to Newton further developing the first reflecting telescope (O'Connor & Robertson, 2002). Although the particle nature of light had been the prevalent one after Newton’s discoveries, other scientists argued that light was indeed composed of waves. One of the biggest contributors to the wave theory of light is Thomas Young (O'Connor & Robertson, 2002). In his remarkable experiments which displayed interference patterns emerging from light waves passing through narrow pinholes, Young demonstrated the wave nature of light (O'Connor & Robertson, 2002). Indeed, Young explained the different colour components of light as being waves of different wavelengths (O'Connor & Robertson, 2002). As we know, in our modern times the prevailing theory is that light is of a dual nature, both waves and particles (O'Connor & Robertson, 2002). There are many various applications for a light theory including photography, medicine (vision defects), astronomy and biology (magnification).

Part 2. The double-slit experiment (14 pts.) Setup used for the experiment: A laser that is able to create a light beam of various wavelengths

A panel with a slit in the middle of variable width A screen with variable distance to the slit. Variables: Wavelength of a light beam (λ) - the longer the wavelength, the more spread-out the light beam on a screen is. Slit width (d)- the larger the slit width, the more concentrated the image is (brighter and smaller). Screen distance (L) - the farther the screen is from the slit, the larger and more blurry the image (and vice versa). Potential inaccuracies: Inaccuracies may result from the difficulties related to positioning the screen at a certain distance from the slit due to the fact that the screen has to be dragged in the app instead of manually inputting the required distance in the software. Laser

Slit separation, d

Distance to

Measured position

Calculated wave-length,

Light

(m)

screen, L (m)

of y1 (m)

λ (nm)

Red

0.0003

4.33

0.01

580 nm

Green

0.0003

4.33

0.009

520 nm

Blue

0.0003

4.33

0.0085

490 nm

Red

0.0005

2.45

0.0035

570 nm

Green

0.0005

2.45

0.003

490 nm

Blue

0.0005

2.45

0.0025

410 nm

0.00025

3

0.009

750 nm

Green

0.00025

3

0.007

580 nm

Blue

0.00025

3

0.006

500 nm

Red

Red laser light λ = 633 nm Green laser light λ = 530 nm Blue laser light λ = 466 nm

Part 3. Polarization of light. (6 pts.) Write a paragraph explaining what polarization of light is, and what it means for the nature of light. Describe two cases of polarization of light seen in nature, or produced by technology. Explain the mechanism of polarization in each case. Give one example of a practical application that uses polarization of light. Light can be explained (in very simple terms) as a wave that vibrates back and forth. Visible light is a mixture of many different light waves all vibrating in different directions as they are traveling (Beiser, 2009). A light that vibrates horizontally produces a glare - and this occurs due to all of the different wavelengths that are simultaneously moving in this direction. In order to polarize a beam of light, one can pass the light through a small opening that is strategically aligned in the same way that you want the waves to be polarized (Beiser, 2009). An example of polarization of light in modern technology would be polarized sunglasses. Fishermen often use polarized sunglasses in order to reduce the glare that is reflected from the water - the use of polarized sunglasses helps them see fish quite clearly. The specific process involved in this technology is as follows: very small slits (visible only by microscope) are made into the polarized sunglasses. These tiny slits align the different light waves resulting in the polarization of light (Cambridge in Colour, 2018). Another example of how polarization appears in modern technology occurs in the use of polarized lenses in the field of photography. As the effects of polarized camera lenses cannot be replicated by modern photo editing techniques, this popular use of light polarization is very important. When polarizers are placed in front of a camera, sunlight that is directly reflected gets filtered (Cambridge in Colour, 2018).

Part 4. Doppler Effect of Light. (5 pts.) The Doppler effect is a phenomenon observed with several types of waves (sound, light,etc.). This phenomenon occurs whenever there is an ongoing change in distance of an observer and a wave source, that is, if the wave source moves either towards or away from the observer (Beiser, 2009). When the wave source is moving away from a (stationary) observer, the eye will encounter fewer wave cycles. This is seen by the eye as a lower frequency colour, called a “red shift” (Urone & Hinrichs, 2018). On the other instance of a wave source moving towards a stationary observer, they will perceive a higher frequency wave (i.e. a shorter wavelength). This is called a “blue shift” (Urone & Hinrichs, 2018). There are many applications of the Doppler effect of light within many scientific disciplines. Some examples include: studying how the planets move relative to each other and the Earth using a light spectrometer (a device that analyzes light waves), satellite tracking in orbit, handheld radar guns that police use to measure speeds of moving vehicles, etc. (Scientific India, 2018).

Lab Journal 2 (12%): Optical Devices

Part 1. Early use of optical devices. (15 pts.) The use of lenses for the purpose of aiding vision was well known in Europe since the 13th century, thanks to the work of Roger Bacon (Bardell, 2004). He was the first to experiment with lenses and the first to establish the rules of refraction of light - these observations led to the development of eyeglasses (Bardell, 2004). Since these first writings about the properties of glass lenses, very little was done in the centuries that followed to further this knowledge. It was in the beginning of the 15th century that brought about the invention of the microscope and the telescope (Bardell, 2004). These two devices both came to light around the same time (around the year 1600), however the exact dates are unknown (Bardell, 2004). The invention of using two lenses one behind the other in order to achieve an image magnification has been claimed by many names; more notably Dutch spectacle makers Hans Jannsen, his son Zacharias, as well as another Dutch instrument maker Jacob Metius (Bardell, 2004). There has been no clear evidence that points towards any one of the

above mentioned names as the inventor, mainly due to the fact that it is a relatively simple setup that could be imitated quickly by a great number of people (Bardell, 2004). Another plausible reason for so many claims to the invention of the (very primitive) telescope is its obvious value as an aid in warfare – it would allow soldiers to spy on their enemy from a far safer distance, and it would result in great financial gain for its inventor (Bardell, 2004). There is very little known about the origin of the first microscope – as with the telescope – since there is no information known about who was the first to build either instrument (Bardell, 2004). A very famous inventor that became immediately interested in the telescope after hearing about its invention in the Netherlands is Galileo Galilei (Bardell, 2004). Galileo immediately set out to improve on the idea of two lenses used together in order to create magnified images of objects (Bardell, 2004). The main goal Galileo was set to fulfill was to build a telescope. He built a microscope and used it to test the reliability of his telescope. He observed the magnified image of an insect, and noted that the enlarged image was indeed that of the insect (not an illusion) – this proved that the images seen on a telescope were also real, and the instrument was reliable (Bardell, 2004). If the image seen through the two lenses of a microscope is real, so is too the image seen through a telescope. Galileo used his telescope to make some of the earliest observations of the stars and planets, including the Milky Way (Bond, 2001). Although he is not credited with the invention of the microscope, the Dutch instrument maker Cornelius Drebbel is one of the first people documented as a microscope-maker (Bardell, 2004). The oldest depiction of a microscope was done by Isaac Beeckman, a Dutch scholar, in 1631 (Fig.1).

Fig. 1 Rough sketch of a tripod microscope, drawn by Isaac Beeckman, 1631.The instrument depicted is a Drebbel model (Bardell, 2004).

The earliest uses for the two-lens microscopes were the observation of small insects and other biological specimens (Bardell, 2004). There were major problems however, mainly due to the spherical and chromatic aberration of light, which resulted in distorted images (Bardell, 2004). An effort to reduce these problems resulted in the single lens microscopes being used. The single lens microscope design was greatly improved by Antoni van Leeuwenhoek who reported many microscopic observations of biological specimens ranging in size from microbes to whales (Bardell, 2004). Robert Hooke was the first to discover the existence of cells and other microorganisms. His observations were made using both single lens as well as compound microscopes, and culminated in his book Micrographia in 1665 – one of the classic works that lead to the development of microscopy (Bardell, 2004). It was also Hooke who improved the design of the compound microscopes by adding an external source of light to the instrument as well as a

thorough description of the objective and ocular lenses of a compound microscope (Bardell, 2004). As time went by, the quality of the lenses produced greatly improved, which led to the development of compound microscopes of great magnification power. This led to the slow demise of the single lens microscopes (Bardell, 2004).

Fig.2. Robert Hooke’s detailed illustration of a compound microscope (Bardell, 2004).

The main similarity between the two designs lies in the fact that both telescopes use two lenses – the objective lens (which is the lens that incoming light from outer space hits), and the secondary lens (which is the lens that refocuses the image to the observer’s eye). For both telescopes the objective lens is a convex lens (The First Telescopes, n.d.). The main difference between the two designs lies in the shape of the secondary lens, as well as the location and orientation of the image. In the Galilean telescope (Fig.3), the secondary lens is a concave lens, and it redirects light from the image formed (in front of the lens) towards the observer’s eye. In the Keplerian refracting telescope the image of the light source is formed behind the secondary convex lens (i.e. falls between the two lenses). This image is the one perceived by the observer (Fig.4). Notably, in the Keplerian telescope, the image seen is actually a converted image, compared to the source image (The First Telescopes, n.d.).

Fig. 3 Galilean refracting telescope (Galilean Telescope, n.d.).

Fig. 4 Keplerian telescope (Keplerian Telescope, n.d.).

One of the main problems that were seen with the earlier refracting telescope designs was chromatic aberration - images were seen as having a “coloured fringe”, or with a “halo” effect, which greatly reduced image resolution (Newton’s Reflectors: The birth of the reflecting telescope gives astronomers options, n.d.). To solve this problem, Newton used a spherical, highly polished mirror instead of the glass primary (objective) lens (Newton’s Reflectors: The birth of the reflecting telescope gives astronomers options, n.d.). Although this was an improvement in telescope design, the new mirror spherical lens caused yet another problem; spherical aberration of the images (images appear blurred) (Newton’s Reflectors: The birth of the reflecting telescope gives astronomers options, n.d.). This problem was difficult to solve at that time, due to technological constraints; it was very difficult to produce highly polished surfaces that were not spherical in shape (Newton’s Reflectors: The birth of the reflecting telescope gives astronomers options, n.d.). This problem was eventually solved with the advent of new technology in the year 1721, when the first non-spherical highly

polished shapes were produced (Newton’s Reflectors: The birth of the reflecting telescope gives astronomers options, n.d.).

Lab Journal 3 (8%): Colour and Sound. Part 1. Mechanisms to generate color. (10 pts.) ● Red in the rainbow

When light passes through water droplets present in the atmosphere, it is reflected, thus creating a rainbow (Rainbows and other colorful phenomena, n.d.). Different parts of the light spectrum are refracted at different wavelengths producing the rainbow progression - red, orange, yellow, green, blue, indigo and violet (Fig.1). The order of the colors observed in a rainbow is not coincidental; the color red is at one end of the spectrum and the color violet is at the other. These reflect the wavelengths in increasing order – red is the lowest and violet is the highest wavelength with the other colors falling in order between them (Dispersion: The Rainbow and Prisms, n.d.). It is worth noting that in order for our eyes to see the rainbow, the light source (i.e. the sun) needs to be at an angle less than 42 degrees above the horizon (Rainbows and other colorful phenomena, n.d.).

Fig.1. Light rays from the sun are reflected from the back of the water drop. These reflected rays are then refracted as they “exit” the droplet thus displaying all the colors of a rainbow (Dispersion: The Rainbow and Prisms, n.d.).

The arched shape of the rainbow is explained by the fact that the parallel rays from the sunlight and the refracted light must be at the correct angle when entering the observer’s eye (from different points in the sky) (Fig.2).

Fig.2 A rainbow is observed as an arc (Dispersion: The Rainbow and Prisms, n.d.).

● Red leaves in the Autumn All plants contain chlorophyll, the chemical that gives them their green color and ability to carry out photosynthesis - converting sunlight into energy (Palm, n.d.). In addition to chlorophyll, plants contain other pigmented substances, such as xanthophyll (yellow pigment) and carotene (orange) (Palm, n.d.). In warmer weather, as well as in evergreens, these pigments are masked by the green colour of chlorophyll. In the fall the days become shorter and the temperatures start to get cooler. Most plants start to enter a hibernation stage, in which photosynthesis is greatly reduced (almost stopped completely) and chlorophyll starts to break down (Palm, n.d.). This results in the other pigments becoming visible; in some plant species a chemical reaction in the leaves results in the production of the brightly colored red anthocyanin pigments (Palm, n.d.). The colour red on the leaves is the result of sunlight falling on the surface of the leaves, and all wavelength colors being absorbed, except red (which is the colour we see) (Palm, n.d.).

Fig.3. A bright display of red colour seen in maple trees in the fall (Milius, 2002).

● Volcanoes Every hot object emits thermal radiation which is generated by the motion of particles in matter. As its temperature rises, the object starts to change its color (Nave, n.d.). Since shorter wavelengths carry more energy, the higher the temperature of an object, the more its color will shift in the order of increasing wavelengths: red (cooler), yellow, and blue when it is hottest (see also Fig. 4) (Nave, n.d.). This phenomenon is also seen in volcanic eruptions that occur in nature (Nave, n.d.). When a volcano erupts and hot magma is released from the earth’s core, it has a distinctive mix of red, orange and yellow colors which are a direct reflection of the temperatures and energy levels that are being transferred with matter (Nave, n.d.). As it flows on the surface and emits its thermal energy, the magma temperature decreases and the colors gradually shift towards their original grey and black (Nave, n.d.).

Fig.4. Different temperatures (in Kelvin scale) display their peaks in different wavelengths. The peak of the 6000K scale falls in the blue region of visible light, whereas the 5000K peak falls in the yellow and the 4000K peak fall in the red region.

Fig.5. The bright red and yellow colors seen in an erupting volcano are a result of the extremely high temperature of ...