# Astronomy 1021 Chapter Notes - Chapter 5: Electromagnetic Spectrum, Photon, Radiography

24 views8 pages
16 Aug 2016
School
Department
Chapter 5: Light: The Cosmic Messenger
Reflection/Scattering
Smooth surface: mirror like reflection in a particular direction
Rough surface: scattering= reflection in a variety of directions
Transmission
Light passing through a medium
The light often "bent" in the process
Called refraction
The sun appears distorted at sunset because of refection in Earth's atmosphere
Absorption
Light may also be absorbed
An object that absorbs all light is opaque
An object that only partially absorbs is translucent
Q: Why is a rose red?
A: The rose reflects red light.
What is light?
Light can act either like a wave or like a particle
Particles of light are called photons
oIts energy depends on frequency
oIt interfere like waves but have momentum like particles
Wave- a pattern of motion that can carry energy w/o carrying matter along with it
oHas 3 interconnected properties:
Wavelength
Frequency
Speed
oFrequency- number of times per second that wave vibrates up and down
Wave speed= wavelength x frequency
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 8 pages and 3 million more documents.

Light is electromagnetic wave
oElectric and magnetic fields are oscillating
oIt interacts w/ charged particles through these electric and magnetic fields
oDoes not need a medium to propagate through
EM waves travel at c: wavelength x frequency = 3.00 x 108 m/s
Wave speed = wavelength x frequency
Shorter wavelength = higher frequency
Longer wavelength = lower frequency
Photon's energy is directly proportional to its frequency
l x f = c
ol = wavelength
oF = frequency
oC = speed of light
E = h x f = photon energy
oH = numerical constant (6.626 x 10-34 joules)
Photons only have "one" distinguishing quality
E.g. two photons of the same blue colour also have the same wavelength, the same
frequency and the same energy: they are identical
White light is made up of many different colours (wavelengths)
We directly experience only same wavelengths of light
Human skin detects infrared light as warmth
Visible light: part of spectrum we see is a tiny fraction
Electromagnetic spectrum has may kinds of light we can't see; different in wavelength,
frequency and energy; speed is constant
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 8 pages and 3 million more documents.

EM regimes
Shortest wavelengths: gamma rays
X-rays: longer wavelength than gamma rays
Ultraviolet : longer wavelengths than X-rays, but shorter than violet we can see
Wavelengths of visible light : 400 nm to 700 nm (1 nm = a billionth of a meter)
Infrared : beyond red, so longer wavelengths still
Microwaves : even longer wavelengths
Order of magnitude λ
Gamma Rays < 10-13 m
X-rays 10-10 m
Ultraviolet 10-8 m
Visible light (400 to 700 nm) 10-7 m
Infrared 10-5 m
Microwaves 10-2 m
Q: The photons in your microwave carry
A: Less energy than the photons from a light bulb
Q: Yes or no: if you had X-ray vision, then you could read an entire book without turning any
pages.
A: No, a book doesn’t emit X-rays so you wouldn’t see anything.
MOLECULES
Smallest entities that still have the properties of the bulk material
oEx. Salt molecules, water molecules, propane molecules
ATOMS
Molecules are made up of even smaller entities called atoms (“indivisible”)
oEX. 1 sodium chloride molecule (NaCl) is made of 1 Na and 1 Cl atom (salt!) 1
water molecule (H2O) is made of 2 H and 1 O
MATTER AND EMPTY SPACE
Atoms themselves are in fact made up of even smaller particles:
oA cloud of electrons (not very massive) on the outside.
oA heavy nucleus consisting of protons and neutrons
Nucleus contains almost all mass of atom, but is about 100,000 times smaller in size
than atom as a whole.
So most of the atom is really empty space
Particles and charge
Fundamental property of particles: electric charge.
Charge is either positive (+) or negative (-).
Opposites attract, same charges repel each other.
Neutrons: no charge.
Protons: positively charged (+)
Electrons: negatively charged (-)
Atoms: as many electrons as protons
oatoms are neutral.
Electrons can be knocked off an atom, and some atoms can capture electrons.
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 8 pages and 3 million more documents.

# Get access

\$10 USD/m
Billed \$120 USD annually
Homework Help
Class Notes
Textbook Notes