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WELCOME TO PERIOD 20: RADIANT
ENERGY FROM THE SUN
Homework #19 is due today.
Midterm 2: Weds, Mar 27, 7:45 – 8:55 pm
(Same room as your midterm 1 exam.)
Covers periods 10 – 19 and videos 3 & 4
Review: Tues, 3/26, 7:00 – 8:00 pm 2005 SM
Drop in: Weds, 3/27, 5:30 – 7:15 pm 2005 SM
Be sure to bring a calculator to the exam!
PHYSICS 1104 – PERIOD 20
•How is radiant energy produced in the Sun?
•How does this energy reach the Earth?
•What properties of waves made energy
transfer possible?
Summary of the forms of energy
Kinetic The energy exhibited by objects in motion.
Thermal The unorganized energy of motion of vibrating atoms
and molecules.
Sound The organized energy of motion of vibrating atoms and
molecules.
Electrical The energy resulting from forces between charged
particles.
Magnetic The energy resulting from the forces between magnets.
Radiant The energy resulting from vibrations of electric charge,
such as radio waves, microwaves, or visible light.
Gravitational The energy stored in raised objects that could fall.
Strain The energy stored in a stretched or compressed spring.
Chemical The energy available in the chemical bonds binding
atoms together.
Electrical The energy stored by static electric charges.
Nuclear Energy available in the nuclei of radioactive atoms.
Energy from electric charge
Stationary electric charge produces an electric force
and has electric potential energy.
Moving electric charge produces an electric current.
Vibrating electric charge produces radiant energy.
(Radiant energy is also called
electromagnetic radiation.)
Radiant energy (electromagnetic radiation)
Radiant energy results from vibrations of charges.
As the charges vibrate, they produce waves of energy.
Waves of electromagnetic radiation travel at a speed of
3 x 108 (300,000,000) meters/second in a vacuum.
The type of radiant energy depends on the wavelength.
Shorter wavelengths transmit more
energy than longer wavelengths.
Types of electromagnetic radiation
The electromagnetic spectrum can be divided into types of radiant energy based on the wavelength and frequency.
The spectrum from the longest wavelength to the shortest:
1) Radio waves used for radio and TV transmission.
2) Microwaves used for communication and in microwave ovens.
3) Infrared radiation, which we experience as thermal energy.
4) Visible light waves are a small portion of the spectrum
5) Ultraviolet light that causes skin tanning
6) X – rays used in medical applications
7) Gamma rays produced in some nuclear reactions.
Some insects can see ultraviolet light
Source:
http://www.dailymail.co.uk/s
ciencetech/article-473897/A-
bees-eye-view-How-insects-
flowers-differently-us.html
Humans see
yellow
flowers in
visible
light.
On the same
flowers, bees can
see patterns in
ultraviolet light.
Nucleons = quark trios Quarks are fundamental particles.
up quark = + 2/3 charge; down quark = - 1/3
Proton consists of 2 up quarks and 1 down quark.
Neutron consists of 1 up quark and 2 down quarks.
For two quarks of the same type (2 up quarks or 2 down quarks), their spins must point in opposite directions.
The gluon is the gauge boson responsible for the strong nuclear force that holds three quarks together to form a neutron or a proton.
Beta decay involves a change in quarks
b+ decay: A proton changes into a neutron.
b- decay: A neutron changes into a proton.
energyenp 0o
01
10
11
energyepn 00
01
11
10
Fusion Fission
Combining of Breaking apart of nucleons or large nuclei small nuclei
Exothermic Exothermic
Total number of nucleons
Fusion in stars: the proton-proton chain Stars smaller than 1.2 times the mass of the Sun use a
hydrogen-burning proton-proton chain as their primary fusion process.
1) two hydrogen nuclei (protons) fuse to form a nucleus of deuterium.
1H + 1H 2H + e+ + e (+1.44 MeV)
2) Deuterium fuses with another hydrogen to form an isotope of helium called tritium.
2H + 1H 3He + (+ 5.49 MeV)
3) Two tritium fuse to form a stable helium nucleus plus two hydrogen nuclei.
3He +3He 4He + 1H + 1H (+12.86 MeV)
Energy release in a star
Radiative zone:
energy transfer by
radiation occurs
when photons
randomly scatter.
Convective
zone: hotter
gases rise
toward to the
surface.
Cooler gases
drop inward.
Nuclear burning region:
fusion in the core of a
star releases energy.
Shape of stars
The gravitational force
exerts an inward pressure on
the core of a star.
Thermal energy from the
core transferred to the star
surface produces outward
radiation pressure.
In a stable star, the outward
radiation pressure of the hot
gas is balanced by the inward
force of gravity.
Inward
force of
gravity
Outward
force of
radiation
pressure
Wave properties
Wavelength and amplitude of a sine wave.
Wave Length
Distance
Wave height (amplitude)
Wave Length
Wavelength, period, and frequency
• The wave’s period is the time it takes to complete one cycle.
• The wave’s frequency is how often it completes a cycle.
Wave Length
Wave Length
Distance
Wave
Period
Wave
Period
Time
Lower frequency Higher frequency
Wave frequency
The period of a wave is the time it takes the wave to
complete one cycle.
The frequency of a wave is the inverse of its period.
frequency = 1/period
Frequency is measured in Hertz (Hz)
1 Hz = 1 cycle/second
Wave speed
The relationship between wavelength and frequency
gives the speed of a wave:
s = f L
s = speed at which radiant energy travels
(meters/sec or mi/sec)
f = frequency (cycles/sec, or Hertz)
L = wavelength (in meters, miles, or feet)
Electromagnetic waves and sound waves
Which type of waves can travel through air?
Which type of waves can travel through a vacuum?
How do the speeds of sound waves and
electromagnetic waves compare?
BEFORE THE NEXT CLASS… Read textbook chapter 21.
Complete Homework Exercise 20.
Print out Activity Sheet 21.
Midterm 2: Weds, Mar 27, 7:45 – 8:55 pm
(Same room as your midterm 1 exam.)
Covers periods 10 – 19 and videos 3 & 4
Review: Tues, 3/26, 7:00 – 8:00 pm 2005 SM
Drop in: Weds, 3/27, 5:30 – 7:15 pm 2005 SM
Be sure to bring a calculator to the exam!
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