Transcript light - pennsphysics

LIGHT
Chapter 27
LIGHT
• Primary source – the Sun
• Secondary sources –
brightness in the sky or
reflection
LIGHT
• we see objects because light
bounces off them
• Light is energy that is
emitted by vibrating electric
charges in atoms that travel
in waves
27.1 Early Concepts
of Light
• 5th century BC – 15th century AD:
scientists believed ‘streamers’
came from our eyes and shined
on objects we saw
27.1 Early Concepts
of Light
Empedocles – light travels in
waves
Isaac Newton – believed light
travels in straight lines, not
waves
Known as the “Particle Theory”
27.1 Early Concepts
of Light
Christian Huygens – sometimes
waves, sometimes particles
Albert Einstein (1905) – published
a theory called “Photoelectric
Effect” that stated that light
consists of particles called
photons
27.1 Early Concepts
of Light
Photons – massless bundles of
concentrated electromagnetic
energy
Today, scientists agree light has a
dual nature:
part particle, part wave
The Speed of Light
• Olaus Roemer (1675):
– The problem of Jupiter’s moons
27.2
The Speed of Light
Speed of light = extra distance traveled
extra time measured
= 300,000,000 km / 1000 sec
= 300,000 km/sec
27.2
The Speed of Light
Albert Michelson (1880):
scientist from America who
theorized on the speed of light
by testing the motion of light in
a moving object
27.2
The Speed of Light
light year – the distance
traveled by light in one year
Example
(You need to know how to work
problems like this)
How far, in kilometers would a
beam of light travel in one
year?
27.3 Electromagnetic
Waves
• waves by which light energy
travels
• Other examples: radio waves,
microwaves, X rays
• all are radiated by vibrating
electrons within an atom
27.3 Electromagnetic
Waves
• All electromagnetic waves are
shown on the electromagnetic
spectrum
(overhead 57)
27.3 Electromagnetic
Waves
• Infrared waves electromagnetic waves with a
frequency lower than red of
visible light
27.3 Electromagnetic
Waves
• Ultraviolet waves (UV)electromagnetic waves with
frequencies higher than those
of violet
Higher in energy (cause
sunburns)
27.4 Light and Transparent
Materials
Transparent - term applied to
materials that allow light to
pass through them in
straight lines
27.5 Opaque Materials
• Opaque - term applied to
materials that absorb light
without reemission and do
not allow light through them
27.6 Shadows
• Ray – thin beam of light
Any beam of light can be
considered a bundle of rays
Shadows are produced
where light rays cannot
reach
Sharp shadows
VS
Blurry Shadows
Shadows
• Umbra – total shadow
• Penumbra – partial
shadow
27.7 Polarization
Light waves are transverse waves.
Polarization – the filtering out of
all vibrations in a transverse
wave, such as a light wave, that
are not in a given direction
Reflection & Refraction
• At boundaries between mediums, waves
can be
• Reflected
• Refracted
• (or Absorbed)
• Reflection – bouncing off
(flat surface parallel to H2O)
• Refraction – penetrating
(goes through from one
medium to the other)
(flat surface perpendicular to
H2O)
Optical Illusions
(overhead 59)
Open Notes Quiz
Define or give the
significance of the following:
1. light
2. Christian Huygens
3. Albert Michelson
4. Ray
5. Polarization