HONOURABLE MENTION

#### How Does Light Intensity Change With Distance

In order to find the relation between light intensity and distance, I measured the intensity of light at four increasing distances away from the light source using a light sensor.

### Hypothesis

If the distance from the light source is increased, the intensity of light will decrease because light gets spread over a larger area.

### Research

Important Terms:

Light Intensity: the amount of visible light that is given off in unit time per unit solid angle.

Brightness: How the human eye distinguishes light

Lux: lumens per square meter

Lumen: brightness of light that is given off by a light source, the amount of illumination in an area.

Visible Light Spectrum: It is o.oo35 percent of the electromagnetic spectrum. It is arranged from low frequency to high frequency, ROYGBIV

Light: Visible light is the only part of the electromagnetic spectrum that the human eye can detect.

Distance: The amount of space between two objects.

Inverse: the opposite in relation, ex. Wavelength is inversely proportional to frequency.

Square: the product of a number multiplied to itself.

Theory: An idea that is proposed in order to explain something.

Optics: The study the behavior and properties of light.

BACKGROUND RESEARCH

Visible Light and The Electromagnetic Spectrum:

The electromagnetic spectrum is the scope of all energy and radiation around us. There are radio waves, microwaves, infrared rays, visible light, ultraviolet rays, x-rays and gamma rays. All of these waves travel at the speed of light in vacuum, but at different frequencies. Radio waves have the lowest frequency, going up to gamma rays which have the most. The wavelength and frequency of a wave are inversely related.

• Radio waves: They have the least frequency in the electromagnetic spectrum. Radio waves are mainly used for sending information from one place to elsewhere and communicating around the globe. They carry signals for TVs and cellular phones and are used in radio navigation systems, air traffic control, wireless networks and more. There are different wavelengths in the radio spectrum. AM radio ranges from 535 KHz to 1705 KHz. FM radio ranges from 88 MHz to 108 MHz.
• Microwaves: Microwaves have a higher frequency and shorter wavelength than radio waves. The main application of microwaves is to heat food. Microwaves are also beneficial to transmitting information due to the fact that energy can go through barriers such as clouds, smoke, snow and light rain. Microwaves are good for viewing Earth from space.  A microwave tower can send information to other cities.
• Infrared waves: Infrared waves are invisible to the human eye but are felt as heat. It has a range of wavelengths just like visible light. Near infrared light is closest to the visible light portion, and far infrared light is closest to the microwave portion of the electromagnetic spectrum. The type of infrared radiation that we experience as heat, is far infrared waves. Infrared light is used in thermal imaging cameras, security systems, electrical heaters, remote controls and more.
• Ultraviolet waves:Ultraviolet waves have a high frequency and shorter wavelength than visible light. Many animals and insects are able to see ultraviolet light. The Ultraviolet portion of the electromagnetic spectrum is divided into three sections. Near ultraviolet (NUV), far ultraviolet (FUV) and extreme ultraviolet (EUV). When in contact with skin ultraviolet light causes tanning. Too much exposure on skin causes sunburns. Scientists can study objects in the universe by using ultraviolet light. Objects in space that are very hot and active, give off a lot of UV energy. UV lamps are used in hospitals to kill microorganisms on the equipment. UV light is also used to treat jaundice.
• X-Rays: X-rays have the second highest energy in the electromagnetic spectrum. They are mainly used for medical imaging. They have a lot of energy and can pass through soft tissue but not bones. The X-ray images that are made are called radiographs. There are many examinations that use X-ray technology such as mammography, computed tomography, fluoroscopy etc. Wilhelm Conrad Roentgen was a German scientist who first observed and documented X-rays.
• Gamma Rays: Gamma Rays have the highest energy on the electromagnetic spectrum. They are produced by nuclear explosions. Gamma rays are also produced in space. Supernovas, black holes and the decay of radioactive material are all sources of gamma rays. Since gamma rays have the highest energy, they can easily go through barriers and would need a lot of dense material such as lead or concrete to stop them. They are capable of killing living cells, and are used in radiotherapy.

Humans are only able to detect visible light, which is around 0.0035 percent of the electromagnetic spectrum. The human eye can distinguish wavelengths from 400 to 700 nanometers. Unlike humans, some animals can see beyond the visible light spectrum. For example, bees, butterflies, reindeers and owls are able to detect ultraviolet light. Mosquitoes, bed bugs and some snake species can detect infrared radiation. The wavelengths of visible light from longest to shortest are red, orange, yellow, green, blue, indigo and violet. White light travels the fastest in vacuum. When white light travels through a prism, it gets refracted and separates into the colors of the visible light spectrum. This is called dispersion.

Characteristics of Visible Light:

Light defines how we perceive reality and experience everything. It is a stream of photons travelling in waves at the speed of light in vacuum. It behaves in many different and mysterious ways. Such as reflection, when light bounces off an object, refraction is when light bends as it goes from one medium to another, or diffraction, when light slightly bends as it travels around the edge of an object. Light waves travel in straight paths, which are called rays. The strength of the wave can get fainter with the distance it travels.

Speed: Light travels exactly 299,798 kilometers per second in vacuum. It can go around the Earth 7.5 times in one second. There is nothing that is faster than the speed of light. The speed of light in vacuum is always faster than the speed of light in a different medium, such as water, because when photons make contact with the molecules in the medium, they slow down.

Many scientists had tried to find the speed of light using different methods. The first person to make an accurate measurement of the speed of light was in 1676 by a Danish astronomer named Ole Romer. He calculated it by observing and timing the eclipses of Jupiter's moon, lo.

Color: Colors are the wavelengths in the visible light spectrum. They range from 400 nanometers to 700 nanometers. The colors from least frequency to greatest are red, orange, yellow, green, blue, indigo and violet, also known as ROYGBIV. Each color has a different frequency and wavelength. If the wavelength of a color is short, then the frequency would be a lot. Violet has the highest frequency and energy, while red has the least. There are also primary and secondary colors of light. The three primary colors are red, blue and green. Amounts of primary colors can be combined to create shades of secondary colors, which are yellow, magenta and cyan. Combining blue and green creates cyan, combining red and green creates yellow and combining red and blue creates magenta. When all secondary colors are mixed, it creates black.

Models and Theories of Light: For ages scientists have been arguing on whether light is a particle or a wave. Sometimes it acts like a wave and other times it acts like a particle.

Particle Model: The particle theory of light was first introduced by Pierre Gasendi, but Sir Isaac Newton expanded it even more. He concluded that light is made up of particles that travel really fast and in straight lines. He believed that light was a particle because the edges of the shadows it created were really clear.  Christiaan Huygen disagreed, and believed that light was a wave.  He claimed that if light was made up of particles, when beams of light crossed, the particles would collide and stop each other. The particle theory had been brought up again by Albert Einstein. He claimed that light is a photon and they flow in a wave action.

Wave Model: The wave theory of light was created by Christiaan Huygens. In 1665, an Italian physicist named Francesco Maria Grimaldi discovered light diffraction, and related it to the behavior of waves. A French physicist named Augustin-Jean Fresnel claimed that the wavelength of light was really short. He also mathematically proved what light interference was and in 1815 he originated physical laws for refraction and reflection of light. In 1817, an English physicist named Thomas Young calculated the wavelengths of light to be one millionth of a meter from an interference pattern. More scientists started to believe that light was a wave and not a particle.

The wave theory of light shows light travelling as a wave, but does not explain all of its unpredictable behaviors. All waves have a crest, trough, amplitude, rest position, wavelength and frequency. The crest is the highest point on the wave, while the trough is the lowest. The amplitude is the vertical distance from the rest position to the crest or trough. The wavelength is the distance between two troughs. The frequency is the number of cycles a wave repeats in a specific amount of time. Frequency is measured in hertz (Hz).

History of the Study of Light:

Research and study for the optics field was first situated in ancient Greece around the 6th to 3rd B.C. Socrates, Plato and Aristotle were Greek philosophers who established the foundation of astronomy, mathematics, biology, optics, philosophy and politics. This is a timeline to understand the major discoveries made about light.

• 600 B.C - Pythagoras was a mathematician and he attempted to explain the concept of vision. He claimed that light beams exit our eyes, and anything the beams touch, we would be able to see. The problem with this theory is that we are not able to see in the dark.
• 300 B.C - Euclid was a Greek mathematician. He summarized the concepts of optics such as vision, reflection and diffusion in his book called Euclid's Optics. He claimed that light travels in straight lines and also initiated the mathematical formula for refraction and reflection.
• 160 A.D  -  Ptolemy was a Roman astronomer. He wrote about refraction and described how light beams bend when they go from air to glass. He also further established the emission theory of light.
• 984  -   Ibn Sahl was a Persian physicist and mathematician. He wrote On Burning Mirrors and Lenses which demonstrated his understanding of how curved mirrors and lenses were able to bend and focus light.
• 1000s  -  Ibn al-Haytham was an Arab astronomer, physicist and mathematician. He is known to be the father of optics because of his great achievements including his Book of Optics. The Book of Optics shows his observations and experiments on light being reflected and refracted using lenses and mirrors. Ibn al-Haytham also stated that vision actually takes place by light rays entering our eyes, this is the intromissionist theory.

• 1200s  -  Roger Bacon was an English philosopher. In 1250 he discovered that light reflects off of objects, and doesn't get released from them.
• 1604  -  Johannes Kepler was a German astronomer and mathematician. In 1604, he discovered how vision works and how eyes focus light.
• 1615  -  Willebrord Snellius was a Dutch astronomer, he explained the relationship between the angle of incidence and the angle of refraction when light passes through one medium to another. This is called Snell's law, but it was first accurately described by Ibn Sahl in 984.
• 1668  -  Sir Isaac Newton was an English astronomer, physicist, mathematician and author. He expanded Pierre Gassendi's idea that light is made up of separate fast moving particles called ''corpuscles.''
• 1672  -  Sir Isaac Newton showed how white light separates into a spectrum of colors when it goes through a prism.
• 1678  -  Christiaan Huygens was a Dutch astronomer, inventor, physicist and mathematician. He was the first to introduce the wave theory of light to explain light reflection and refraction.
• 1801  -  Thomas Young was a British scientist. In 1801 he conducted the '' double slit experiment'' which gave him strong evidence and proof that light is actually a wave. The particle theory of light had been replaced by the wave theory.
• 1860  -   James Clerk Maxwell was a Scottish theoretical physicist. He predicted the existence of electromagnetic waves and explained that electricity, magnetism and light are all indications of the electromagnetic field.
• 1905  -  In 1905 Albert Einstein established the photoelectric effect theory, where light is made up of particles called photons.

Luminous Intensity and the Inverse Square Law:

Luminous intensity is the amount of visible light that is given off in unit time per unit solid angle. It is measured in terms of lumens per square meter, or lux. Lumens refer to the brightness of light that is given off by a light source, it is the amount of illumination in an area. Brightness and light intensity are different. Light intensity is a physical quantity, while brightness is how the human eye distinguishes light.

Many physical properties such as luminosity decrease as they get further away from something. This decrease can be demonstrated by the inverse square law. The inverse square law is a mathematical term and scientific law that describes the way energy travels through space from a light source. It was proposed by Isaac Newton.

In this drawing, the light from the flashlight shines on the screen one meter away from it. Light rays from the flashlight spread out as they travel further. If there was a second screen that is two meters away from the flashlight, in order for the second screen to catch the same light rays as the first screen, it needs to be twice as wide and twice as tall. This is because light rays spread out as they travel. The second screen is four times bigger than the first screen, so the illumination on this screen is only 1/4 of the first screen.

If there was a third screen that is three meters away from the light source, it would need to be three times as wide and tall to catch the same light rays as the first screen. The illumination on this screen is only 1/9 because light is going to be spread out nine times as much area than the first screen.

So, as the distance from a light source increases, the intensity of light decreases because light becomes spread over a larger area. The relation between light intensity and distance is inverse.

### Variables

Controlled Variables: type of light bulb, type of light sensor,  area where the light intensity is recorded.

Manipulated Variable: Distance between the light bulb and the light sensor.

Responding Variable: The change in light intensity as the distance from the light source increases.

### Procedure

Area:

1. Find an area of two by three meters to do the experiment.
2. Area must be completely darkened, if there are windows nearby, cover them with black poster paper so that it doesn't affect the result.
3. Cover walls, floor or reflective objects with black poster paper so that it doesn't affect the results. This helps because black is the least reflective color, and absorbs all light.
4. Cover the wall sockets with black tape, except the socket that the light bulb will plug into.

Light Sensor:

1. Download '' Arduino Science Journal'' on smartphone or tablet.
2. After the tutorial, click the ''sensors'' icon near the bottom to access the light sensor.
3. After the ''sensors'' icon is clicked, it will automatically start recording the light intensity (lux) and the sound intensity (dB). We only need to observe the light intensity.

Setting Up:

1. Create an observation chart to record the distance from the light bulb (cm), the three trials, and the average of the three trials.
2. Have the smartphone, light bulb and ruler in the darkened area.
3. Place the ruler on the black poster paper on the floor.
4. Place the light bulb on the 0 cm point on the ruler.
5. Light bulb must be at the same height as the light sensor on smartphone. A ball of clay can be placed under the light bulb so that it aligns with the light sensor.
6. Smartphone must be able to move smoothly on the ruler to record the light intensity.

Experimenting:

1.  After the area and light sensor is set up, wear sunglasses and turn on the light bulb.

2. Using the ruler, make a 10cm, 20cm , 30cm and 40cm mark on the floor covered with black poster paper.

3.Place the smartphone at the 10cm point.

4. The app will then tell how intense the light is at 10cm away from the light source.

5. Record the light intensity (lux) in the observation chart in trial one.

6. Do two more trials. In the observation chart, write the intensity in trial 2 and 3.

7. Record the average of all three trials in an observation chart.

8. After all three trials on the 10cm mark are noted, move the smartphone to the 20cm mark.

9.Note down the intensity of light at the 20cm point for three trials.

10. Record the average of the three trials in the chart.

11. Move the smartphone to the 30cm point.

12. Note down the light intensity at the 30cm point for three trials in the  chart.

13. Record the average of those three trials in the chart.

14. Lastly, move the smartphone to the 40cm point.

15. Record the light intensity for three trials in the chart.

16. Record the average of the three trials in the chart.

17. In the end, the observation chart should have all the 4 distances from the lightbulb, all 3 three trials for the 4 distances ,and the averages of the trials for all 4 distances.

Cleaning Up:

Turn off the light bulb and put it in a safe place, take off sunglasses since  the light bulb is turned off and remove black poster paper from windows, walls, wall socket,floor and any shiny reflective objects that were covered. Put the ruler, smartphone and sunglasses away.

### Observations

OBSERVATIONS/RESULTS

When  the smartphone was 10cm away from the light source, the average intensity after three trials was 996 lux.  When the smartphone was 20cm away from the light source, the average intensity was 597 lux, when it was 30cm away from the light source, the average intensity was 350 lux. Lastly when I had the smartphone 40cm away from the light source, the average intensity was only 242 lux. After my experiment, I found out that as I increased the distance of the smartphone from the light bulb, the light intensity continued to decrease from 996 to 242 lux. Looking at the line graph, the line is going down as the distance increases for each of the trials.

### Analysis

When the sensor was 10cm away from the light source, the light intensity on the first trial was 1000 lux, on the second trial it was 988 lux and on the third trial it was 1000 lux. The average of these three trials is 996 lux.

When the sensor was 20cm away from the light source, the light intensity on the first trial was 600 lux, on the second trial it was 595 lux and on the third trial it was 597 lux. The average of these three trials is 597 lux.

When the sensor was 30cm away from the light source, the light intensity on the first trial was 350 lux, on the second trial it was 353 lux and on the third trial it was 348 lux. The average of these three trials is 350 lux.

When the sensor was 40cm away from the light source, the light intensity on the first trial was 241 lux, on the second trial it was 242 lux and on the third trial it was 243 lux. The average of these three trials is 242 lux.

Each time, I increase the distance of the sensor from the smartphone by 10cm. When the sensor is at the closest point, 10cm, the light intensity is the highest. But as the distance from the light source increases the light intensity decreases. At 10cm from the light source, the average intensity was 996 lux, but at 40cm from the light source, the average intensity was 242 lux. 996 is greater than 242. So, in conclusion, when the distance from the light source increases, the light intensity decreases.

### Conclusion

In order to find out how distance from a light source changes the intensity of light, I moved a light sensor away from the light source at four different distances. After doing my experiment, I found out that light intensity does change when you increase the distance, and that my hypothesis was proven correct. The data I collected after doing my experiment does show that the light intensity decreased as I increased the distance from the light bulb. The average light intensity after three trials went from 996 lux at 10cm from the light bulb to 242 lux at 40cm from the light  bulb. As you increase the distance of an object from a light source, the intensity of light decreases. This is because light gets spread over a larger area. As the distance between interacting objects increases, the strength of the property decreases.  This change can be demonstrated by the inverse square law. The inverse square law is seen as a force, such as light or radiation, that is spreading out over an area that is continuously increasing each time . It tells us how the intensity of light is inversely related to distance.

### Application

- Light intensity is measured in Photography and Cinematography. Low light levels makes the photographer have to open the lens aperture or increase exposure time. In Cinematography, by measuring light levels, the cameraman can make consistent results.

-  Scientists calculate the light intensity of a star to find out how far away it is from Earth. Astronomers look at a star's color spectrum to determine the star's brightness. Scientists can then determine Earth's distance to the star by comparing the star's brightness to the detectable brightness seen from Earth,

- Light sensors are used in agriculture. Water supply is less in areas of the world, and farmers have a responsibility to limit their use of water while also keeping their crops hydrated. In farms, light sensors are used to manage the sprinkler system, the crops are only watered when the sun is dim. When light sensors are also accompanied by weather-monitoring equipment, they could detect rain or clouds and adjust the schedule.

- Light sensors are used to place art in appropriate locations. Places like entrances or windows of museums have too much sunlight, which could harm the art. Light sensors are used to calculate the right distance to place the art in the building.

I could do this experiment better next time by having more space to conduct my experiment, have 5 trials instead of 3 to get an even more accurate result, cover area with more black poster paper or use more than one app for recording the light intensity.

### Sources Of Error

Environmental Error: Light enters the dark area and causes the sensor to record the wrong light intensity. The light sensor was not directly aligned with the light source.

Estimation Error: The wrong distances from the light source area labelled on the floor.

Human Error: The wrong data is recorded.

### Citations

• Luminosity and the Distance to Stars. Retrieved January 29, 2021, from https://www.atnf.csiro.au/outreach/education/senior/cosmicengine/stars_luminosity.html

• Electromagnetic Spectrum - Introduction. (n.d.). Retrieved from https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

• Visible Light. (n.d.). Retrieved January 29, 2021, from https://science.nasa.gov/ems/09_visiblelight#:~:text=WAVELENGTHS OF VISIBLE LIGHT,narrow band of the spectrum.

• (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/visible.html

• Visible Light. (n.d.). Retrieved January 29, 2021, from https://science.nasa.gov/ems/09_visiblelight#:~:text=WAVELENGTHS OF VISIBLE LIGHT,narrow band of the spectrum.

• Radio Waves. (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/radio.html

• Microwaves. (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/micro.html

• The Infrared. (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/infrared.html

• Ultraviolet Waves. (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/uv.html

• X-rays. (n.d.). Retrieved January 29, 2021, from https://www.nibib.nih.gov/science-education/science-topics/x-rays#:~:text=X-rays are a form,and structures inside the body.

• Gamma-rays. (n.d.). Retrieved January 29, 2021, from https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/gamma.html

• History of research on light. (n.d.). Retrieved January 31, 2021, from https://photonterrace.net/en/photon/history/#:~:text=Through the research accumulated over,a wave and a particle.&text=For human beings, history of,may have only just begun.

• Inverse square law. (n.d.). Retrieved January 31, 2021, from https://energyeducation.ca/encyclopedia/Inverse_square_law#:~:text=Specifically, an inverse square law,1/4 as much exposure.

• Elert, G. (n.d.). The Nature of Light. Retrieved January 31, 2021, from https://physics.info/light/#:~:text=Light is a transverse, electromagnetic,can travel through a vacuum.

• Canon : Canon Technology: Canon Science Lab: Light is It a Wave or a Particle? (n.d.). Retrieved January 31, 2021, from https://global.canon/en/technology/s_labo/light/001/11.html

• Light ideas and technology – timeline. (n.d.). Retrieved January 31, 2021, from https://www.sciencelearn.org.nz/resources/1867-light-ideas-and-technology-timeline

• Scientific calculations - direct and inverse proportion - Higher - Photosynthesis - Edexcel - GCSE Combined Science Revision - Edexcel - BBC Bitesize. (n.d.). BBC News. Retrieved February 8, 2021, from https://www.bbc.co.uk/bitesize/guides/ztc297h/revision/7#:~:text=There%20is%20an%20inverse%20relationship,spread%20over%20a%20wider%20area.

• Morgan, J. (n.d.). Light Sensors: Units, Uses, and How They Work. Retrieved January 31, 2021, from https://blog.endaq.com/how-light-sensors-work

• Exploring Our Fluid Earth. (n.d.). Retrieved January 31, 2021, from https://manoa.hawaii.edu/exploringourfluidearth/physical/world-ocean/map-distortion/practices-science-scientific-error#:~:text=Common sources of error include,how they affect the results.

### Acknowledgement

I would like to express my gratitude to my science teacher Mrs. Aulakh who gave me the golden oppurtunity of participating in the Calgary Youth Science Fair and also helped me throughout my project. I would also like to thank my parents who helped me in finializing this project, I am really thankful to them.