LIGHT

1. LIGHT

2. Theories of Light Is light made up of particles or waves?

3. Whether or not light was composed of particles of waves was the subject of vigorous debate.

4. Particle v. Wave Theories Sir Isaac Newton proposed that white light was actually made up of colored particles which combined to appear white. The theory that light was composed of particles was known as the “corpuscular “ (particle) theory.

5. Newton experimented with prisms and observed that what light was composed of a spectrum of colors. He conducted many experiments and at one point pushed a “bodkin needle” into his eye socket, putting pressure on his eyeball to see how that would effect his vision.

6. Newton ‘s book on light was first published in 1704.

9. Christian Hyugenspublished his Treatise on Light in 1690, in which he proposed that light traveled in the form of waves. (ALSO: Huygens made many astronomical discoveries. He was first to use a pendulum to regulate a clock. In 1659 he derived the now standard formula for the centripetal force, exerted on an object.

11. Light is a form of Electromagnetic radiation. Max Planck, at the turn of the 20th century, proposed that light, as well as some other forms of radiation, are generated by interacting electric and magnetic fields.

12. Planck developed the quantum theory in which energy is emitted from atoms in discrete units called quanta.

13. Einstein applied Planck’s idea to the photoelectric effect in which he proposed that atoms absorbed or emitted energy in bundles called photons. Therefore, light was made up of quanta called photons.

14. Louis de Broglie proposed that all particles, as well as photons, act like standing waves which vibrate at specific and discrete or quantized frequencies.

15. Erwin Schrödingerdeveloped a generalized equation to describe the “particle-wave” characteristic. “The Schrödinger equation is the fundamental equation of physics for describing quantum mechanical behavior. It is also often called the Schrödinger wave equation, and is a partial differential equation that describes how the wave function of a physical system evolves over time.”-Science World

16. Niels Bohr proposed the Copenhagen interpretation of quantum theory, which asserts that a particle is whatever it is measured to be (for example, a wave or a particle), but that it cannot be assumed to have specific properties, or even to exist, until it is measured. Einstein & Bohr

17. In short, Bohr was saying that objective reality does not exist. This translates to a principle called superpositionthat claims that while we do not know what the state of any object is, it is actually in all possible states simultaneously, as long as we don't look to check.

19. The Schrödinger’s cat paradox.

22. IN SUMMARY: Light is a type of electromagnetic wave, which means that it is produced by an interaction of oscillating electric and magnetic fields.

23. AND… The current model of light incorporates aspects of both particle and wave theories. This is known as wave particle duality.

24. AND… Light is emitted from luminous bodies in little packets of energy called photons. Since each photon is associated with light waves of specific frequencies, it can be said that there is a definite quantity of energy proportional to each frequencyknown as quanta.

25. AND: • Particle-like behavior: photons can collide and interact with electrons and other tiny particles of matter • Wave-like behavior: photons move through space in a probability wavewhich specifies the likelihood that a photon’s energy will be found at a given point on a wave front. (Interacting probability waves account for interference, diffraction, and other wave-like properties of light.)

27. How the human eye works FromLiveScience.com Thecorneaa transparent structure found in the very front of the eye, helps to focus incoming light. Behind the cornea is a colored ring-shaped membrane called the iris.

28. The iris has an adjustable circular opening called the pupil, which can expand or contract depending on the amount of light entering the eye. A clear fluid called the aqueous humorfills the space between the cornea and the iris.

29. Situated behind the pupil is a colorless, transparent structure called the crystalline lens. • Ciliary musclessurround the lens. The muscles hold the lens in place but they also play an important role in vision. (When the muscles relax, they pull on and flatten the lens, allowing the eye to see objects that are far away. To see closer objects clearly, the ciliary muscle must contract in order to thicken the lens.)

30. The interior chamber of the eyeball is filled with a jelly-like tissue called the vitreous humor. • After passing through the lens, light must travel through this humor before striking the sensitive layer of cells called theretina.

31. Theretinais the innermost of three tissue layers that make up the eye. • The outermost layer, called the sclera, gives most of the eyeball its white color. (The cornea is also a part of outer layer.) • The middle layer between the retina and sclera is called the choroid. (The choroid contains blood vessels that supply the retina with nutrients and oxygen and removes its waste products.)

32. Embedded in the retina are millions of light sensitive cells, which come in two main varieties: rods and cones. Rod and Cone

33. Rods are good for monochrome vision in poor light, while cones are used for color and for the detection of fine detail. Cones are packed into a part of the retina directly behind the retina called the fovea. Blue = Nuclei

34. When light strikes either the rods or the cones of the retina, it's converted into an electric signal that is relayed to the brain via the optic nerve. The brain then translates the electrical signals into the images we see.

35. “The Luminous and the Illuminated” • Anything that gives off light is luminous. • Anything upon which light falls becomes illuminated. The hand is illuminated by the luminous bulb.

36. The strength of a light source is called the luminous intensity, measured in units called candelas. A candela is the rate at which 1/60th of a square centimeter emits light. A 40 watt incandescent bulb has an intensity of about 35 candelas.

37. Alternatively: The rate at which light falls upon a unit area of a surface is called the intensity of illumination and is measured in lumens.

38. Intensity of Illumination or Luminous flux If a 1 candela light source is placed at the center of a imagined sphere-shaped area of 1m radius, the rate at which light falls upon 1 square meter of the inner sphere surface is 1 lumen.

39. The Luminous flux will stay the same for a given light source. (Luminous flux is the same for every sphere.) But, the amount of light falling upon a surface decreases with the distance from the light source. Luminous flux divided by the area of the surface, which is called the illuminance(measured in lm/m2 or lux) decreases as the radius squared when moving from the light source. Serway/Faughn –Physics pg 446

40. What is the difference between Lumens & Lux? • Lumens, also known as luminous flux, is the measure of the perceived power of light from a natural or artificial light source. In simple terms it is the measurement of how bright a bulb or tube is.Whether you are 1 meter away or 100 meters away from a light source it is still emitting the same amount of lumens. • Lux is the measure of the apparent intensity of light hitting or passing through a surface at a given distance. A light source 1 meter away will have a far greater lux than if you were 10 meters away. • So in summary the difference between the units Lumen and Lux is that Lux takes into account the area over which the luminous flux is spread at a FIXED distance. Whereas Lumens is the amount of light coming from a light source irrespective of the distance. Daylightco.com