Transcript PHY 108 – Atoms to Galaxies

PHY 102 – Atoms to Galaxies
PHY 102 – Atoms to Galaxies
Our early human ancestors most
certainly looked at the night sky,
and wondered.
Chapter 8:
Light & Electromagnetism
Waves
Wave
Not a material object, but a moving pattern:
bumps on the surface of water,
deformations of music strings, variations
in air pressure, oscillations of
electromagnetic fields, etc.
Two types of waves:
1. Transversal: Waves with
propagating direction perpendicular
to the oscillation direction.
2. Longitudinal: Waves with
propagating direction parallel
to the oscillation direction.
Two principles:
1. Speed: Waves move at a constant speed
that is determined by the medium where they
travel, rather than the waves themselves.
2. Superposition: If two or more waves arrive
simultaneously at the same place, the
resulting effect is simply the sum of the
effects of the waves.
Speed of sound
in various media:
Moving bumps and periodic waves
(http://members.aol.com/nicholashl/waves/waves.htm)
wavelength l (m): length of the wave
frequency f (/s): number of oscillations over time
faudible 20 to 20,000 Hz (humans)
faudible < 20 Hz
faudible > 20,000 Hz
wavelength l (m)
frequency f (1/s)
faudible 20 to 20000 Hz
wave speed v = l f
vsound = 340 m/s
vlight = 300 000 000 m/s
= 300 000 km/s
= 186 450 mi/s
If Earth-Sun distance
is 92 million miles
(150 million km),
how long for the
light from the Sun
to reach the Earth?
17th century physics: planets
Many 17th century scientists
did not believe in “speed
of light.”
Galileo …
1670's, the Danish
astronomer Ole Roemer
discovered that Io didn't
always appear where it
was supposed to be.
c = 300 000 km/s
1888, H. Hertz generated
EM waves in his lab.
Christian Huyghens
In 1673 reported
synchronization
between two
pendulum clocks
hanging on the
same wall.
Superposition: If two or more waves
arrive simultaneously at the same
place, the resulting effect is simply
the sum of the effects of the waves.
Interference: Result of different waves
traveling through the same medium
interacting with one another.
Interference
When periodic waves arrive at the same place
from two synchronized sources, or from the
same source but traversing two different
paths, they produce an interference pattern.
Interference
Difraction:
Process by which waves spread out as a result
of passing a narrow aperture, or across an
edge, typically accompanied by interference
between the wave forms produced beyond the
aperture or edge.
Difraction: Thomas Young, 1803.
Light: Particle or Wave?
From the mid-1660s on Newton conducted a series of
experiments on the composition of light, and established
the modern study of optics. He adopted the corpuscular
theory of light according to which light is made of tiny
particles emitted in all directions by a source.
The theory explained well reflection: a reflecting force
would push the light particles away from the surface.
Reflection
Light: Particle or Wave?
Newton discovered that white light is
composed of the same system of colors
that can be seen in the rainbow.
Refraction
Light: Particle or Wave?
Newton’s corpuscular theory of
light had a few difficulties, such
as explaining refraction.
Light: Particle or Wave?
From the
diffraction
experiment
with light
there is good
evidence that
light is a
wave.
Light
George McCoy
So the concept of light as a wave
goes beyond the visible spectrum.
Question: If light is a wave, what medium is light
traveling through on its way from the
Sun to Earth?
This and other questions were being asked in
the 1800’s. The answer is intrinsically related to
electricity and magnetism.
Light as a wave:
Light is an electromagnetic wave
traveling through an
electromagnetic field.
Electricity
Form of energy resulting from the
existence of charged particles, such as
electrons or proton.
(Thesaurus Dictionary)
From experiments we know that the
charge of the proton (+e) exactly equals
the charge of the electron (-e),
where e = 1.6 x 10-19 coulomb.
Electricity
Law of conservation of electric charge: During any
process, the net electric charge of an isolated
system remains constant (is conserved).
Fundamental characteristic of electric charges:
Like charges repel and
unlike charges attract each other.
Electricity
Coulomb’s Law:
The magnitude of the electrostatic force exerted
by one point charge q1 on another point charge
q2 is directly proportional to the magnitude of
the charges and inversely proportional to the
square of the distance r between them:
F = k q1 q2 / r 2
where k = 9 x 109 N m2/C2.
Magnetism
Two nearby bar magnets either attract or repel
each other.
The ends of a bar magnet are called north and
south magnetic poles.
Each bar magnet has two poles. “Monopoles” are
yet to be found.
Magnetism
Fundamental characteristic of magnetic poles:
Like poles repel and
unlike poles attract each other.
This attraction (or repelling) force is a new
type called magnetic force.
Magnetism
Experiments show that electrically charged objects
that are moving exert and feel an additional force
beyond the electric force that exists when they are
at rest. This additional force is the magnetic force.
All magnetic forces are caused by charges in motion.
The Electric Atom
The planetary model of
the atom depicts the
atom as almost entirely
empty, divisible and
made of many parts.
Nucleus (constituted of
neutrons and positively
charged protons)
surrounded by tiny
negatively charged
electrons.
The Electric Atom
Order of magnitude:
the overall size of an
atom is about 10-10 m.
The nucleus is about
10,000 times smaller
than the atom.
A scaled-up model
of the atom with
a nucleus the size
of a soccer ball
would have the
electrons as dust
specks several
kilometers away.
The Electric Atom
Order of magnitude:
the overall size of an
atom is about 10-10 m.
The nucleus is about
10,000 times smaller
than the atom.
A scaled-up model
of the atom with
a nucleus the size
of a soccer ball
would have the
electrons as dust
specks several
kilometers away.
Faraday’s Law
When a wire loop is placed in the vicinity of a
magnet and when the loop or the magnet is
moved, an electric current is created within the
loop for a long as the motion continues,
or,
A changing magnetic field creates an electric field.
The principle of electric power generation
Chapter 9:
Electromagnetic Radiation
Electromagnetic radiation
James C. Maxwell,
Scottish, in the
1860s developed
a theory that
unified electricity
and magnetism.
Electromagnetic radiation
Every vibrating charged object
creates a disturbance (wave) in
its own electromagnetic field.
This disturbance spreads
outward through the field at
light-speed, 300,000 km/s .
Light is just such an
electromagnetic wave.
Electromagnetic radiation
Heinrich Hertz,
German, in the 1890s
demonstrated
experimentally that
electromagnetic waves
can travel in space and
induce oscillations at a
distance from where
they were generated.
Electromagnetic radiation
Guglielmo Marconi,
Italian, in the late
1890s developed
wireless telegraphy
which became the
basis for the radio and
television revolution.
Ether
The Newtonian clockwork
model had no room for
new phenomena like light
traveling in ‘empty’ space
 ether  Hypothetical
medium for transmitting
light and heat (radiation),
filling all unoccupied
space.
• all attempts to
demonstrate its
existence, most
notably the
Michelson-Morley
experiment of
1887, produced
negative results
Field
• Field: a region of
space characterized
The special theory of
by a physical
relativity, proposed
property, such as
by Albert Einstein in
gravitational or
1905 eliminated the
electromagnetic
need for a lightforce or fluid
transmitting medium.
pressure, having a
determinable value
at every point in the
region.
Solar Radiation and Earth
Solar Radiation and Earth
Solar Radiation and Earth
Ozone Depletion
Ozone depletion:
1928, GMC, inert chlorofluorocarbons (CFCs)
Where are CFCs going? Crutzen, Molina, Rowland (1974)
u-v radiaton  Chlorine (Cl)
Cl + O3  ClO + O2
ClO + ClO + sunlight  Cl + Cl + O2
A single Cl atom destroys about 100,000 ozone molecules!
Ozone Depletion:
Susan Solomon, 1986
Global Warming
Hypothetical
Earth with
normal
atmosphere
except for
no
greenhouse
gases.
Global Warming
Realistic Earth
with normal
atmosphere
including
trace
amounts of
greenhouse
gases.
Global Warming
Global Warming
Atmospheric concentration of
carbon dioxide between
1000 and 2003.
Global Warming
Global Warming
Global Warming
Carbon dioxide
concentration
and
temperature
Global Warming
Global Warming Consequences
1.
2.
3.
4.
5.
6.
7.
Climate zones shift about 500 km away from Equator
1.25 million species extinction by 2050
Accelerate Greenland and Antarctic ice melting
Increase rate of sea level rise
Mixed agricultural effects
Thrive of mosquitoes and other disease vectors
Northward spread of tropical diseases (malaria, dengue)
Global Warming: What to do?
1997, Kyoto: Industrialized nations agreed to reduce
their greenhouse gases emission 5% below 1990
levels by the year 2012.
1. As of 2001, emissions were 10% above 1990 levels
2. Actually, 60%-80% reduction is needed
3. The U.S. with 4.5% of world’s population emits 23%
of world’s carbon, did not sign the Kyoto Protocol.
Global Warming: Precautionary Principle
Scientific uncertainty should not be a reason
to postpone measures to prevent harm.
Chapter 10: Special Theory
of Relativity
In the late 1800s it
was believed that
the era of new
discoveries in
fundamental
physics was likely
ended. The future
would be to
improve the
accuracy of known
results. But …
In 1900 the German
physicist Max Planck
introduced a
revolutionary idea,
the quantum of
energy. The new
idea was hardly
noticed, initially.
Special Theory of Relativity
In 1905 a different
but also
revolutionary
idea was
introduced by a
patent clerk in
Switzerland,
Albert Einstein.
Galilean Relativity
Relative motion
Reference frame
vball/train = 20 m/s
vtrain/ground = 70 m/s
vball/ground = ?
Galilean Relativity
Relative motion
Reference frame
c = 300,000 km/s
vlight/ship = c
vship/ground = 0.25 c
vlight/ground = ?
The Principle of Relativity
Every non-accelerated observer observes
the same laws of nature,
or
No experiment performed within a sealed
room moving at an unchanging velocity
can tell you whether you are standing
still or moving.
The Principle of the
Constancy of Lightspeed
The sped of light (any electromagnetic radiation) in
empty space is the same for all nonaccelerated
observers, regardless of the motion of the light
source or the observer.
1964, fast subatomic irradiating particle
experimental evidence.
Michelson-Morley experiment, 1887, ether
Time is relative
If the speed (distance over
time) of light is constant,
then perhaps we need to
revisit the concepts of
distance and time.
Let’s measure time with a
light clock from two distinct
reference frames.
Mort and Velma use identical clocks and
measure different time intervals for the
same event: the relativity of time.
Mort and Velma use identical clocks and
measure different time intervals for the
same event: the relativity of time.
tM = time interval
measured by Mort
tM = time interval
measured by Velma

v = speed of ship
(relative speed)
c = lightspeed
tM 
t
tV
1
2
v
1 2
c
Duration of one clock tick
(1 second in the clock’s
reference frame)
on a clock moving relative
to the reference frame.
Muon ’s lifetime has
been shown to be
different depending
on their speed.
Fast muons live longer.
Time Travel: Back to the Future?
Velma (assumed same age as
Mort) travels away at 0.75c
relative to Mort and comes
back after 60 years on
Mort’s clock. How old will
she be upon her return?
Relativity of Space and Mass
Time and space are tangled
up with each other.
Length contraction
Space is different for different
observers.
Mort and Velma use identical meter sticks
and measure different lengths for the same
object: the relativity of space.
LM = lenght measured by
Mort
LM = length measured by
Velma
v = speed of ship
(relative speed)
c = lightspeed

LM  LV
2
v
1 2
c