Conceptual Physics

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# Conceptual Physics - PowerPoint PPT Presentation

Conceptual Physics. Notes on Chapter 27 Light. Light. Early Concepts of Light Up until the time of Newton, most scientists thought that light was a particle. Dutch scientist Christian Huygens said light was a wave. Then in 1905, Einstein said light was

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### Conceptual Physics

Notes on Chapter 27

Light

Light

Early Concepts of Light

Up until the time of Newton, most scientists thought that light was a particle. Dutch scientist Christian Huygens said light was a wave.

Then in 1905, Einstein said light was

small particles - massless bundles of

energy that behaved like waves called

photons.

Light

Speed of Light

In 1675, a Danish

astronomer named Olaus

Roemer demonstrated that

light travels as a finite speed

Roemer’s Experiment pg. 405

• Dutch scientist Huygens looked at Roemer’s data and calculated the speed of light to be 300,000 km/s.
Light
• In 1880, an American scientist named Albert Michelson performed a experiment using a spinning mirror to find the speed of light.

Michelson’s Experiment

Light
• Michelson speed for light (the excepted value today) is 299,920 km/s.

NOTE: We will use Roemer’s rounded

number of 300,000 km/s.

Light

FUN FACTS

• Light would travel 7.5 times around Earth in one second.
• Light takes 8 minutes to travel from the Sun to Earth - a distance of 93,000,000 miles.
• Traveling at the speed of light, it would take 4 yrs to travel to the nearest star.
Light

Electromagnetic Waves

• Electromagnetic Spectrum is a continuous range of waves extending from the longest (Radio) and going to the shortest (Gamma).
Light
• Any material that allows light to pass through in straight lines is said to be transparent.
• EX: Glass

Water

• Any material that absorbs light w/o reemission is said to be opaque.
• EX: Wood

Stone

Light

• A thin beam of light is called a Ray. When light rays can not go past an object, a shadow is formed.

Two parts of a shadow are:

• EX: Solar and Lunar Eclipses
• See pg. 413 Fig. 27.12 & 27.13
Light

POLARIZATION

• Light is a transverse wave. White light is Non-polarized.
• When passed through a

filter (Polarizer) only light

that is moving same as the

filter opening will make it

through.

• See pg. 415

Fig. 27.18