Light Physics Ms. Johnson. Early Concepts Most philosophers and scientists believed light consisted...
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Transcript of Light Physics Ms. Johnson. Early Concepts Most philosophers and scientists believed light consisted...
Light
Physics
Ms. Johnson
Early Concepts
• Most philosophers and scientists believed light consisted of particles
• Christian Huygens was the first to argue that light was a wave
• In 1905, Einstein published a paper on the photoelectric effect, where he explained light consisted of particles called photons
• Scientists now agree that light has a dual nature, as a particle and as a wave
Speed of Light
• Several different measurements– Pre - 17th century
– Galileo
– Olaus Roemer 1676
– Michelson (1926)
• Represented by the symbol c =3.0x10^8 m/s• Light-year - distance light travels in one year
Electromagnetic Waves
• Light is energy that is emitted by accelerating electric charges
• This is called an electromagnetic wave
• This is a transverse wave• This wave type includes
radio waves, microwaves, x-rays which are all part of the electromagnetic spectrum
• Visible light has a wavelength from 400nm – 700nm
• Red light has the lowest frequency
• Violet has the highest.• Waves with a frequency
lower than red light are infrared
• Waves with frequencies higher than violet are ultraviolet
Types of Electromagnetic Waves
Transparent & Opaque
• Transparent materials allow light to pass through them
• Light can slow down as it passes through these materials– Ex: glass- .67c water
- .75c
• Opaque materials allow no light to pass through them.
• A material can be transparent to some wavelengths and opaque to others
Shadows
• A thin beam of light is called a ray.
• Any beam of light can be thought of as a bundle of rays
• When a beam of light shines on an object, some of the rays may be stopped while others may continue on their straight-line path
• A shadow is formed where light rays cannot reach.
• A total shadow is called an umbra
• A partial shadow is called a penumbra - it occurs when some light is blocked but other light fills in
Eclipse
• An eclipse is an example of a shadow
• When the moon is between the sun and Earth it casts a shadow– The darkest part of the shadow is the umbra– The lighter, outer part is the penumbra
• There are 2 types of eclipses, solar and lunar
Lunar vs. Solar Eclipse
Polarization
• Light travels in transverse waves that go out in all directions
• When waves are polarized, they are only allowed to travel in one direction
• Filters can be used to create polarized light
• If two polarizing filters are placed at 90° to each other, no light will get through.
Polarized Glasses
3D Viewing
• Seeing in 3 dimensions depends on both eyes giving the same impressions simultaneously.
• A pair of photos placed a short distance apart
• This can be done in slide shows or movies by projecting 2 polarized pictures on the same screen and viewing it through 2 different polarized lenses