Light

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Nature of Lightas Waves

Nature of Lightas Waves

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What is Light?

•The natural agent that stimulates sight and makes things visible.

•Electromagnetic radiation from about 390 to 740 nm in wavelength.

"Is light a wave or a stream of

particles?"

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Let’s first analyze characteristics

behaviors of light as a wave.

Reflection

•All waves are known to undergo reflection or the bouncing off of an obstacle.

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Refraction

• Change in direction of propagation of any wave as a result of its traveling at different speeds at different points along the wave front.

• All waves are known to undergo refraction when they pass from one medium to another medium.

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Diffraction

• Diffraction involves a change in direction of waves as they pass through an opening or around an obstacle in their path.

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Interference

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• In 1807, Thomas Young (1773-1829) did the most convincing experiment demonstrating that light is a wave.

• A beam of light fell on a pair of parallel, very thin slits in a piece of metal.

• After passing through the slits, the light fell on a screen.

• A pattern of alternating bright and dark bands formed is called an interference pattern.

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Interference

• Wave interference is a phenomenon that occurs when two waves meet while traveling along the same medium.

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Polarization

• Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming un-polarized light into polarized light is known as polarization.

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Polarization

• The fact that light shows polarization tells us that light is a transverse wave.

• Transverse waves are waves that cause the particles of the medium to vibrate perpendicularly to the direction of motion.

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Polarization Hint

• Light vibrates in all directions.• A polarizing filter acts like a

picket fence. It only lets certain direction vibrations pass through it.

• Therefore, if you pass light through two of them you can completely block the light from passing through.

• HOW?

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Polarization

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Now what about the particle-like

behavior?

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The photoelectric effect is observed when light of a certain frequency strikes a metal and ejects electrons.

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Phenomenon

Can be explained in terms of waves.

Can be explained in terms of particles.

Reflection

Refraction

Interference

Diffraction

Polarization

Photoelectric effect

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What is Light?

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• Light is a special type of wave.• What we know as light or

VISIBLE LIGHT is actually a type of something called ELECTROMAGNETIC RADIATION.

• So, what is electromagnetic radiation and electromagnetic waves?

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Electromagnetic Radiation

• When something creates energy it also emits radiation. Depending on the amount of energy, the object will emit different types of electromagnetic radiation.

• When we studied mechanical waves, they were all transferred through a medium. What medium is light transferred through?

LIGHT DOES

NOT NEED ONE!

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Electromagnetic Waves

• Electromagnetic waves are waves that do not need a medium to propagate through.

• But what is creating the disturbance? What is emitting this energy?

ELECTRONS

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• Electromagnetic waves are everywhere.

• Light is only a small part of them

– Radios– TVs– Microwaves– Light

(Visible/UV/InfraRed)

– Radiation– Lasers– CD/DVD

players– X-Rays

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• Electrons in materials are vibrated and emit energy in the form of photons, which propagate across the universe.

• Photons have no mass, but are pure energy.

• Electromagnetic Waves are waves that are made up of these “photons”.

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The Corpuscular Theory• Created in the seventeenth

century by Sir Isaac Newton • States that light emitted by

luminous objects consist of tiny particles of matter called corpuscles. When corpuscles hit a surface, each particle is reflected.

• Thought that light traveling from air into water will increase the speed, while light entering water will decrease the speed.

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The Wave Theory

• Discovered by Christian Huygens, a Dutch scientist, also in the seventeenth century

• States that light is emitted in a series of waves that spread out from a light source in all directions. These waves are not affected by gravity.

• Furthermore, he disagreed with Newton and said that light traveling from air to water will decrease the speed, and vice versa. Huygens was proved later to be correct.

• 100 years later, Englishman Thomas Young completely disproved the corpuscular theory by showing that light waves can interfere with each other.

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The Electromagnetic Theory

• Discovered in the nineteenth century by James Maxwell

• Proposed that light waves do not require a medium for transmission.

• Light waves posses electrical and magnetic properties and can travel though a vacuum. Light waves are a part of a larger family of electromagnetic waves and make up the electromagnetic spectrum.

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The Quantum Theory

• Discovered by Max Planck, German scientist in 1900

• Stated that light waves travel as separate packets of energy called quanta or photons.

• Merged the subjects of the Corpuscular, Wave, and Electromagnetic Theories together.

• Later, it was proved that the correct and most accurate theory was the Quantum Theory.

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•Quantum Theory explains that light has both properties of waves and particles thus,

light is both wave and particle.

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Both particles and waves?!?What the hell?!

© 2003 Mike Maloney 34


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Yes! Malapit

na recess!!!


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