Transcript Week3 lecture part 2: nature of light

nature of light
By reading this chapter, you will learn
5-1 How we measure the speed of 5-8 The relationship between
atomic structure and the light
light
emitted by objects
5-2 How we know that light is an
5-9 How an object’s motion affects
electromagnetic wave
the light we receive from that
5-3 How an object’s temperature
object
is related to the radiation it
emits
5-4 The relationship between an
object’s temperature and the
amount of energy it emits
5-5 The evidence that light has
both particle and wave aspects
5-6 How astronomers can detect
an object’s chemical
composition by studying the
light it emits
5-7 The quantum rules that
govern the structure of an atom
Determining the
Speed of Light
Galileo
Olaus Rømer
(1676)
Fizeau and Foucalt (1850)
d=rt again gave c
I. Newton - particle-like properties
C. Huygen – wave nature
Young’s Double-Slit Experiment – wave like properties (1801)
James Clerk Maxwell (1860s)
wave nature: electromagnetism
• Because of its electric and
magnetic properties, light is
also called
electromagnetic radiation
• Visible light falls in the 400
to 700 nm range
• Stars, galaxies and other
objects emit light in all
wavelengths
electromagnetic radiation
around you
Three Temperature Scales
See box 5-1 (pg. 105)
Temperature conversion
•Tf = 9/5 Tc +32
•Tc = 5/9 (Tf -32)
•TK = Tc + 273
How are you doing?
1. Who was the first person to come up with a
method to measure a reasonable value of
speed of light?
2. Huygen’s idea of light was light as _____,
which was different from Newton’s view of
light. A) particle, b) wave, c) part of
electromagnetic radiation, d) photons of
various energy level
3. Light part of electromagnetic radiation. What
type of electromagnetic radiation is high
energy? A) radio wave, b) visible light, c)
Ultraviolet, d) infrared, e) gamma ray
Put the following color in the order of cooler to hotter:
Yellow, Red, Orange, Blue, white
Black body radiation
Wien’s law
lmax ~ 1/Temp
Stefan-Boltzmann law
Luminosity ~ T4
Planck’s law
E ~1/l
This is the method we
used to determine the
surface temperature of
the sun.
@1AU, we receive
1370W /m2
Each chemical
element produces
its own unique set
of spectral lines
Kirchhoff’s
Laws
Doppler effect
• Red Shift: The object is
moving away from the
observer
• Blue Shift: The object is
moving towards the observer
Properties of light
1. Which color is hotter? A) blue, b) red, c) yellow, d)
white
2. Which type of sprctra is produced by hot thin gas? A)
continuous spectrum, b) absorption spectrum, c)
emission spectrum
3. Longer wavelength means: a) higher energy, b)
lower energy
4. Bohr model explains:
5. If a star is moving away from us, the star will suffer:
a) blue shift, b) red shift, c) both blue and red shift.
6. If a star is rotating fast, the star will suffer: a) blue
shift, b) red shift, c) both blue and red shift.