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.

Visible light spectrum

Source: www.elektor.de

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!