The uncertainty about the speed of light in water remained unresolved for over one hundred years after Newton's death. Summary: From the debate over the nature of light between huygens and Newton, we can learn that Scientific lawsare descriptionsof patterns and phenomena of the nature.(e.g. Laws of reflection, laws of refraction) Scientific theories are explanations of such patterns and phenomena.(e.g. Particle theory of light, wave theory of light) A good theory should have strong explanatory power. (Newtons particle theory of light has a greater explanatory power than huygens wave theory of light.) people tend to submit to authority when there is not enough evidence to make judgment. (People believed Newtons theory due to his reputation in science.) In the setup investigating the photoelectric effect (as shown below the intensity of the light, its frequency, the voltage and the size of the current generated are measured.
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(2) Light, unlike sound waves, can travel through a vacuum. Particles can travel through a vacuum. In the 17th century, it was believed that waves could not essay travel through a vacuum. It was difficult for people at that time to believe that waves could travel through the ether, which was the imaginary medium that light travels through, proposed by huygens. X (3) Particle theory of light can explain why there are different colours of light. Huygens could not explain why light has different colours at all. He did not know that different colours of light have different wavelengths. Though Newtons explanation was not correct (particles of different colours of light have different mass and size his particles theory could explain this phenomenon logically in the 17th century? (4) Reputation of Newton people tend to accept authority when there is not enough evidence to make judgement. Newtons particle theory could only explain refraction by incorrectly assuming that light travels faster in a denser medium. No one could prove he was wrong at that time.
The Ideal Gas Law). Kinetic model Law hierarchical relationship? Theory hypothesis Newton was the winner. (at that time!) Newtons particle theory of light dominated optics during the 18th century. Most scientists believed Newtons particle theory of light because it had greater explanatory power. Lets consider the reasons waves do not travel only in straight lines, so light cannot yardage be waves. Sounds can easily be heard around an obstacle but light cannot be seen around an obstacle. Light, unlike sound, does not demonstrates the property of diffraction and it is unlikely to be a type of wave.
What is a scientific theory? What are the differences between them? What is a scientific law? Scientific laws are descriptions of relationships among phenomena or fuller patterns in nature. Ideal Gas Law pv nrt what is a scientific theory? Scientific theories are the explanations of those relationships and patterns. Kinetic Theory law and theory The Ideal Gas Law describes the relationships among p, v, and t of ideal gases. Kinetic Theory explains these relationships (i.e.
C air W1 ptically denser medium W2 d θ2 Click here for animation If light behaves as waves, diffraction and interference should be seen. These are two important features of waves. This was known in the 17th century.(you can see this easily with water waves in a ripple tank) The wave theory of light predicts interference and diffraction. However, huygens could not provide any strong evidence to show that diffraction and interference of light occurred. Diffraction and interference of water waves The laws of reflection and the laws of refraction are examples of laws. The particle theory of light and the wave theory of light are examples of theories. What is a scientificlaw?
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Each point on the wavefront starts a secondary wavelet. These secondary wavelets interfere to form essay a new wavefront w at time. P how can wave theory explain the laws of Reflection? When wavefront W1 (AC) reaches point a, a secondary wave from A starts to spread out. When the incoming wavefront reaches b, the secondary wave from A has reached d, giving a new wavefront W2 (BD). Angle of incidence angle of reflectioncan be proved by renal geometry. Refer to the appendix of the worksheet or your textbook for the proof.
1 W2 lick here for animation How can wave theory explain the laws of Refraction? Wavefront W1 reaches the boundary between media 1 2, point a of wavefront W1 starts to spread out. When the incoming wavefront reaches b, the secondary wave from A has travelled a shorter distance to reach. It starts a new wavefront. As a result the wave path bends towards the normal. Θ1 n1sinθ1 n2sinθ2 can be proved by geometry.
Newton explained this observation by assuming that light travels faster in water, so it bends towards the normal. (What was the problem in this explanation?) The problem: does light really travel faster in water? In fact nobody could measure the speed of light at the time of Newton and huygens Air Cannon ball Light Water Why does a prism separates a beam of white light into the colours of the rainbow? Why does red light refract least and violet light refract most? Newtons assumptions: The light particles of different colours have mass.
Red light particles have more mass than violet particles. All light particles experience the same refracting force when crossing an interface. Thus, red light particles with more inertia will be refracted less by the same force than violet light particles by the same force. Lets see how huygens used his wave theory to explain the characteristics of light i think light is emitted as a series of waves in a medium he called aether (source: Treatise on light, published by huygens in 1690) (aether commonly also called ether) How. A wave starts at p and a wavefront W moves outwards in all directions. After a time, t, it has a radius r, so that r ct if c is the speed of the wave.
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Yet if the ball is thrown with greater and greater speed, its path curves less and less. Thus, billions of plan tiny light particles of extremely low mass travelling at enormous speeds will have paths which are essentially straight lines. How does the particle theory explain the laws of Reflection? The rebounding of a steel ball from a smooth plate is similar to the reflection of light from the surface of a mirror. Steel Ball Rebound Light Reflection Many light particles in a light ray mirror How does Newton's particle theory explain the laws of Refraction? A cannon ball hits the surface of water, it is acted upon by a refracting force which is perpendicular to the water surface. It therefore slows down and bends away from the normal. Light does the opposite.
Interface n2 θ2, light bends towards the normal when it travels from an optically less dense medium to an optically more dense medium. Refracted light ray, newton proposed his particle theory of light (or corpuscular theory of light) to explain the characteristics of light.(source: Opticks, published by Isaac Newton in 1704). I think light is a stream of tiny particles, called Corpuscles. Why does light have different colours? Particle Theory The particles of different colours have different properties, such as mass, size and speed. Why can light travel through a vacuum? Light, internship being particles, can naturally pass through vacuum. (At Newtons time, no known wave could travel through a vacuum.) Why does light travel in straight lines? A ball thrown into space follows a curved path because of gravity.
can travel through a vacuum. Light can be reflected and refracted, these processes are described by the laws of Reflection and Laws of Refraction. Laws of Reflection, according to the laws of Reflection, angle of incidence angle of reflection (θi θr ). Incident light ray, reflected light ray, normal. Willebrord Snell discovered in 1621 that when a wave travels from a medium of refractive index, n1, to one of different refractive index, n2, n1sin(θ1) n2sin(θ2 this relationship is called Snells Law. Laws of Refraction, incident light ray, normal.
Download Presentation, an Image/Link below is provided (as is) to download presentation. Download Policy: Content on the website is provided to you as is for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. Presentation Transcript, a long time ago, aristotle (. In Platos time (427 list 347. the reflection of light from smooth surfaces was known. He was also a greek. The ancient Greeks (about 200.
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Download, skip this Video, loading SlideShow in 5 Seconds. Nature of Light PowerPoint Presentation, download Presentation. Nature of Light 1 / 41, dates nature of Light Nature of light What am I? A long time ago aristotle (. an ancient Greek thinker, thought that we saw the world by sending something out of our eye and that reflected from the object. Copyright Complaint Adult Content Flag as Inappropriate. I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.