Transcript Intro to Physics - Fort Thomas Independent Schools

Intro to Physics
2nd semester topics for final exam
pt. 2
Waves
Mechanical waves
• Fastest through solids,
slowest through gases
• Can only travel through
matter
• Ex: sound, seismic waves
Non-mechanical waves
• Fastest through a vacuum,
slowest through solids
• Can travel through matter
or space
• Ex: electromagnetic waves
ARE THERE DIFFERENT TYPES OF
WAVES?
• Mechanical Waves
• Non-Mechanical Waves
Sound waves
microwaves
Electromagnetic Wave
http://www.nrc-cnrc.gc.ca/obj/inmsienm/images/research_images/optical_comb/COMBFIG1.gif
Waves
Transverse
• Vibrations occur
perpendicular to wave
travel
• Crest, trough structure
Longitudinal
• Vibrations occur in same
direction as wave travel
• Compression-rarefaction
structure
TRANSVERSE WAVE
crest
One
wavelength
amplitude
trough
Rest
position
LONGITUDINAL WAVE
Rarefaction
(less dense)
Compression
(more dense)
one
wavelength
Wave Characteristics
Wave Characteristics
– Frequency (f) (the number of vibrations that
occur in a given time)
• Hertz (Hz) (# of vibrations per second)
• High frequency waves produce waves with
short periods and short wavelengths
– Period (P) (the time it takes for one wave cycle to
pass)
• Seconds (s)
• The lower the frequency, the longer the period
Wave Characteristics
– Wavelength λ (lambda) (the distance between one
point on a wave to the next identical point; crest to
crest, for example)
• Meters (m)
• The lower the frequency, the longer the wavelength
– Amplitude (longitudinal waves—the tightness of the
compression; transverse waves—the distance from the
crest to rest position or from trough to rest position)
• Meters (m)
• The greater the amplitude of the wave, the more
energy the wave transfers.
Sound waves
Sound waves and the Ear
What is the audible range of
frequencies for a human?
20 -20,000 Hz
What type of
wave is a sound
wave?
Mechanical and
The frequency of
a sound wave is
called pitch.
Longitudinal
Like all mechanical waves,
sound waves can only travel
through matter
Relative intensity of sound
wave is volume and is
measured in decibels (dB)
Seismic waves
Cause
• Any physical disturbance that
causes the Earth to vibrate
– Earthquakes (most commonly)
– Volcanoes
– Landslides (terrestrial or undersea)
– Extraterrestrial impacts (asteroids
– and meteorites)
Earthquakes
• Earthquakes occur when built-up stress is
suddenly released.
• Rupture or slippage of rock within the
Earth produce seismic waves
http://quake06.s
tanford.edu/cen
tennial/tour/sto
p11.html
Earthquakes
2
Earthquake Waves
• Earthquake waves
travel out in all
directions from a point
where strain energy is
released. This point is
the focus.
• The point on Earth’s
surface directly above
the focus is the
epicenter.
2
Body Waves—
seismic waves that pass through the Earth
Primary waves, also called P-waves, are
longitudinal waves (compressional).
• P-waves pass through solids and liquids
• P-waves are faster than s-waves.
Secondary waves, also called S-waves are
transverse waves.
• S-waves can travel through solids but
not liquids
• S-waves are slower than p-waves
Body
Fig. 9-8, p. 194
Fig. 9-10, p. 196
Three types of plate boundaries
1.
Divergent plate boundary
2. Convergent Plate Boundary
3. Transform Plate boundary
Fig. 1-14, p. 18
The Mechanism for Plate Motion is Convection in the Mantle
Heat from the interior flows outward toward the crust
Fig. 1-12, p. 15
P-waves
and Swaves
provide
seismic
evidence
that the
outer core is
liquid and
the inner
core is solid
Refraction:
the bending
of a wave as
it passes from
one medium
to another
Caused by
changes in
wave speed
Fig. 9-21, p. 210
Benioff Seismic Zone
(associated with a subduction zone at
a Convergent Plate Boundary)
Pattern of
earthquake
occurrences
indicates the
location of
the
subducted
limb of the
lithospheric
plate
Fig. 2-13, p. 37
Electromagnetic Spectrum
Increasing photon energy
WHAT CAUSES Electromagnetic waves
(or LIGHT)?
• Vibrating electrically charged particles
• A changing electric field sets up a
changing magnetic field, which sets up a
changing electric field, and so on.
Electromagnetic wave (a
combination of electric
and magnetic fields
HOW DO WE MODEL LIGHT?
• TWO MODELS
– Wave Model
– Particle Model
• Physicists recognize the dual nature of light
(light travels like a wave, but hits like a particle).
• Photon: a massless particle of light (carries
energy—greater the frequency, the greater the
photon energy)
INTENSITY OF LIGHT
• An increase in the number of waves or
photons (or the amount of light)
• Brightness of light means intensity.
• Not related to frequency or the energy
per photon!
Same frequencies
of light, just
different
intensities!
100 Watts
40 Watts
Photoelectric Effect: the ejection of electrons from certain
metals when exposed to certain frequencies of light.
Electromagnetic radiation
(visible light range)
Electrons emitted
Photovolatic cell
(solar cell)
Produces electron flow (electricity)
29.2 The Law of Reflection
Incident rays and reflected rays make equal angles with a line perpendicular to the
surface, called the normal.
• The angle between the incident ray and the normal is the angle of incidence.
• The angle between the reflected ray and the normal is the angle of reflection.
• Angle of incidence = Angle of reflection
29.4 Diffuse Reflection
Diffuse reflection allows us to see most things around us.
a.
Light is diffusely reflected from paper in many directions.
b.
Light incident on a smooth mirror is only reflected in one direction.
Ordinary paper has a rough surface
when viewed with a microscope.
29.8 Refraction of Light
As a light wave passes from air into water, its
speed decreases.
Refraction
• The bending of light as it passes from one
medium to another.
• Dependent upon
– Change in light wave speed
– Change in direction
• Bending means an abrupt change in direction.
31.1 Diffraction and Huygens’ Principle
The extent to which the water waves bend depends on the size of the opening.
25.7 Interference
Interference patterns occur when waves from different
sources arrive at the same point—at the same time.
25.7 Interference
a.
In constructive interference, the waves reinforce each other to produce a wave of
increased amplitude.
Amplitude
has doubled
in height
25.7 Interference
a.
b.
In constructive interference, the waves reinforce each other to produce a wave of
increased amplitude.
In destructive interference, the waves cancel each other and no wave is produced.
INTERFERENCE
• The combination of two or more waves that exist in
the same place at the same time.
• Constructive Interference (additive effect—in phase)
• Destructive Interference (subtractive effect—out of
phase)
• http://www2.biglobe.ne.jp/%7Enorimari/science/Jav
aEd/e-wave3.html
• http://www2.biglobe.ne.jp/%7Enorimari/science/Jav
aEd/e-wave2.html
Light and colors
• Primary colors of light
• Red-green-blue
What is color?
• When we see color, we are seeing specific
frequencies of visible light
• VISIBLE LIGHT IS ROYGBIV
• Red, orange, yellow, green, blue, indigo and violet
• For visible light
– Red has the lowest frequency and longest wavelength
– Violet has the highest frequency and shortest wavelength
Isaac Newton—discovered that white light is
composed of seven different colors of light
Red
Orange
White
Light
Yellow
Green
Blue
Indigo
Violet
A prism disperses white light
into its primary frequencies of
color
28.2 Color by Reflection
a.
b.
This square reflects all the colors illuminating it. In sunlight, it is white.
When illuminated with blue light, it is blue.
This square absorbs all the colors illuminating it. In sunlight it is
warmer than the white square.
Electricity
• More electrons than
protons
• Negatively charged
• More protons than
electrons
• Positively charged
Voltage
• Force that causes charges to move (the push
or the electric field)
• Voltage exists if there is a potential difference
in charges (negatively charged vs. positively
charged)
• SI unit is Volt (V)
Electric Current
• The flow of charged particles.
• Charges move from a position of higher to
lower electric PE (or higher voltage to lower
voltage).
• SI unit is ampere (A or amps)
Resistance
• Resistance restricts the flow of electric
charges.
• The cause: internal friction as moving charged
particles collide.
• Unit for resistance is ohm
Series circuit
Parallel circuit
http://iss.cet.edu/electricity/pages/a17.xml
Match statements with the correct
circuit
•
1
2
3
4
5
6
Series circuit
vs.
Parallel circuit
1. other bulbs go out if one bulb burns out
2. bulbs maintain same brightness if more bulbs are
added
3. two or more paths for electric current to flow
4. bulbs dim if more bulbs are added
5. other bulbs stay lit if one bulb goes out
6. only one path for electric current to flow