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Nature of Light.


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Nature of Light Nature of light What am I? Particles? Waves? A long time ago …… Aristotle (384 - 322 B.C.), an ancient Greek thinker, thought that we saw the world by sending “something” out of our eye and that reflected from the object.
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Slide 1

Nature of Light

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Nature of light What am I? Particles? Waves?

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quite a while back …… Aristotle (384 - 322 B.C.), an antiquated Greek scholar, imagined that we saw the world by sending “something” out of our eye and that reflected from the article. In Plato’s time (427 – 347 B.C.), the impression of light from smooth surfaces was known. He was likewise a Greek. The old Greeks (around 200 A.D.) likewise initially watched the refraction of light which happens at the limit of two straightforward media of diverse refractive records.

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In the17 th century, two researchers had diverse perspectives about the way of light …… Light is particles No! Light is waves Isaac Newton 1643 - 1727 Christian Huygens 1629 - 1695

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In the 17 th century, a few properties of light were surely understood as of now. For instance: Light has distinctive hues. Light can go through a vacuum. Light can be reflected and refracted, these procedures are portrayed by the Laws of Reflection and Laws of Refraction .

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Laws of Reflection According to the Laws of Reflection , angle of rate = edge of reflection ( θ i = θ r ) Incident light beam Reflected light beam Normal θ i θ r

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Willebrord Snell found in 1621 that when a wave goes from a medium of refractive list, n 1 , to one of distinctive refractive file, n 2 , n 1 sin(î¸ 1 ) = n 2 sin(î¸ 2 ) This relationship is called Snell’s Law Laws of Refraction Incident light beam Normal θ 1 n 1 Interface n 2 θ 2 Light curves towards the ordinary when it goes from an optically less thick medium to an optically more thick medium. Refracted light beam

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Newton proposed his “particle hypothesis of light” (or “corpuscular hypothesis of light”) to clarify the qualities of light. (source: “ Opticks”, distributed by Isaac Newton in 1704) I think light is a flood of small particles, called Corpuscles …

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Why does light have distinctive hues? Molecule Theory The particles of distinctive hues have diverse properties, for example, mass, size and rate. Why can light go through a vacuum? Light, being particles, can actually go through vacuum. (At Newton’s time, no known wave could go through a vacuum.)

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Why does light go in straight lines? A ball tossed into space takes after a bended way as a result of gravity. Yet in the event that the ball is tossed with more noteworthy and more noteworthy velocity, its way bends less and less. In this manner, billions of small light particles of amazingly low mass going at huge velocities will have ways which are basically straight lines .

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How does the molecule hypothesis clarify the Laws of Reflection? The bouncing back of a steel ball from a smooth plate is like the reflection of light from the surface of a mirror. Steel Ball Rebound Light Reflection Many light particles in a light beam Mirror

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How does Newton's molecule hypothesis clarify the Laws of Refraction? A gun ball hits the surface of water, it is followed up on by a “refracting” power which is opposite to the water surface. It hence eases off and twists far from the ordinary. Light does the inverse. Newton clarified this perception by expecting that light voyages quicker in water so it twists towards the typical. (What was the issue in this clarification?) The issue: Does light truly travel faster in water? Actually no one could gauge the rate of light at the season of Newton and Huygens Air Cannon ball Light Water

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Why does a crystal isolates a light emission light into the rainbow's shades? Why does red light refract minimum and violet light refract most? Newton’s suppositions: The light particles of diverse hues have mass. Red light particles have more mass than violet particles. 2. Every single light molecule encounter the same refracting power when crossing an interface. Subsequently, red light particles with more dormancy will be refracted less by the same power than violet light particles by the same power .

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Let’s perceive how Huygens utilized his “wave theory” to clarify the qualities of light … I think light is discharged as a progression of waves in a medium he called “aether” (source: Treatise on light, distributed by Huygens in 1690) (“aether” ordinarily additionally called “ether”)

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How do waves engender? A wave begins at P and a “wavefront” W moves outwards in all bearings. After a period, t, it has a sweep r so that r = ct if c is the wave's velocity. Every point on the wavefront begins an auxiliary wavelet. These auxiliary wavelets meddle to frame another wavefront W ’ at time t ’ . P

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How can wave hypothesis clarify the Laws of Reflection? At the point when wavefront W 1 (AC) achieves point An, an optional wave from A begins to spread out. At the point when the approaching wavefront achieves B, the auxiliary wave from A has come to D, giving another wavefront W 2 (BD). Point of frequency = Angle of reflection can be demonstrated by geometry. Allude to the worksheet's supplement or your course reading for the verification. C D W 1 W 2 A B Click here for liveliness

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How can wave hypothesis clarify the Laws of Refraction? Wavefront W 1 achieves the limit between media 1 & 2, point An of wavefront W 1 begins to spread out. At the point when the approaching wavefront achieves B, the optional wave from A has ventured out a shorter separation to achieve D. It begins another wavefront W2. Accordingly the wave way twists towards the ordinary. θ 1 n 1 sinî¸ 1 = n 2 sinî¸ 2 can be demonstrated by geometry. Allude to the informative supplement of the worksheet or your course reading for the confirmation. C Air W 1 B An Optically denser medium W 2 D θ 2 Click here for liveliness

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If light acts as waves, diffraction and impedance ought to be seen. These are two essential elements of waves. This was known in the seventeenth century. (You can see this effortlessly with water waves in a “ripple tank”) The wave hypothesis of light predicts impedance and diffraction. In any case, Huygens couldn't give any solid proof to demonstrate that diffraction and obstruction of light happened. Diffraction and impedance of water waves

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The “ Laws of reflection” and the “Laws of refraction” are cases of laws. The “particle hypothesis of light” and the “wave hypothesis of light” are cases of speculations. What is an investigative law? What is an investigative hypothesis? What are the contrasts between them?

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What is an exploratory law? Logical laws are depictions of connections among wonders or examples in nature e.g. Perfect Gas Law PV = nRT What is a logical hypothesis? Investigative hypotheses are the clarifications of those connections and examples e.g. Dynamic Theory

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Law and hypothesis The Ideal Gas Law portrays the connections among P, V, and T of perfect gasses. Motor Theory clarifies these connections (i.e. the Ideal Gas Law). Active model

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Law Hierarchical relationship? Hypothesis

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A hypothesis won't transform into a law or the other way around ! Logical hypotheses and laws are various types of learning.

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If you were one of the researchers in the 17 th century, would you trust the “particle hypothesis of light” or the “wave hypothesis of light”? Why? Clue: Which hypothesis has a more noteworthy capacity to clarify the qualities of light?

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Newton was the “winner”….. (around then!) Newton’s molecule hypothesis of light overwhelmed optics amid the 18 th century. Most researchers trusted Newton’s molecule hypothesis of light on the grounds that it had more prominent informative force . Let’s consider the reasons……

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Waves don't travel just in straight lines so light can't be “waves”. Sounds can without much of a stretch be heard around an obstruction however light can't be seen around a hindrance. Light, not at all like sound, does not shows the property of diffraction and it is unrealistic to be a sort of wave.

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(2) Light, not at all like sound waves, can go through a vacuum. Particles can go through a vacuum. In the 17 th century, it was trusted that waves couldn't go through a vacuum. It was troublesome for individuals around then to trust that waves could go through the “ ether”, which was the nonexistent “medium” that light goes through, proposed by Huygens. X

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(3) Particle hypothesis of light can clarify why there are diverse shades of light. Huygens couldn't clarify why light has diverse hues by any stretch of the imagination. He didn't realize that diverse shades of light have distinctive “wavelengths”. Despite the fact that Newton’s clarification was not right (particles of distinctive shades of light have diverse mass and size), his particles hypothesis could clarify this wonder consistently in the 17 th century. ?

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(4) Reputation of Newton People have a tendency to acknowledge “authority” when there is insufficient proof to make judgment. Newton’s molecule hypothesis could just clarify refraction by inaccurately accepting that light voyages quicker in a denser medium. Nobody could demonstrate he wasn't right around then. The instability about the pace of light in water stayed uncertain for more than one hundred years after Newton's demise.

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Summary: From the open deliberation over the way of light in the middle of Huygens and Newton, we can discover that … Scientific laws are depictions of examples and marvels of the nature. (e.g. Laws of reflection, Laws of refraction)