Martin D. Weinberg UMass Astronomy...

Read: Chap 5 09/25/12 – slide 1

A100–Exploring the Universe: Light!

Martin D. Weinberg

UMass Astronomy

weinberg@astro.umass.edu

September 25, 2012

Announcements

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 2

MasteringAstronomy tutorials

⊲ You must click the “S” button to save your work

before clicking “Submit”

⊲ Animations and exercises are 50% each

⊲ Check system requirements!

Announcements

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 2

MasteringAstronomy tutorials

⊲ You must click the “S” button to save your work

before clicking “Submit”

⊲ Animations and exercises are 50% each

⊲ Check system requirements!

Today: finish Gravity & Orbits

Today: Light and Electromagnetism (LIGHT, Chap. 5)

⊲ How do we experience light?

⊲ How do light and matter interact?

⊲ What is light? What are its properties?

⊲ What is the structure of matter?

Announcements

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 2

MasteringAstronomy tutorials

⊲ You must click the “S” button to save your work

before clicking “Submit”

⊲ Animations and exercises are 50% each

⊲ Check system requirements!

Today: finish Gravity & Orbits

Today: Light and Electromagnetism (LIGHT, Chap. 5)

⊲ How do we experience light?

⊲ How do light and matter interact?

⊲ What is light? What are its properties?

⊲ What is the structure of matter?

Questions?

Gravity and Orbits

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 3

Summary

Planets obey the same laws as objects on Earth

Gravity and Orbits

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 3

Summary

Planets obey the same laws as objects on Earth

Kepler’s laws: explained by force of gravity

⊲ Planets orbit around the center of mass of the Solar

System

⊲ Since most of the mass is the Sun, Sun is very close

to center of mass

⊲ Third law depends on the sum of the two masses:

P 2 =

[

4π2

G(m1 +m2)

]

a3

Gravity and Orbits

⊲ Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 3

Summary

Planets obey the same laws as objects on Earth

Kepler’s laws: explained by force of gravity

⊲ Planets orbit around the center of mass of the Solar

System

⊲ Since most of the mass is the Sun, Sun is very close

to center of mass

⊲ Third law depends on the sum of the two masses:

P 2 =

[

4π2

G(m1 +m2)

]

a3

New types of unbound orbits — hyperbolas and

parabolas — in addition to ellipses

Orbits revisited

Announcements

⊲ Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 4

How do gravity and energy together allow usto understand orbits?

Total orbital energy (gravitational + kinetic) stays

constant if there is no external force

Orbits cannot change spontaneously.

Changing an orbit

Announcements

⊲ Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 5

What can make an object gain

or lose orbital energy?

Friction or atmospheric

drag

A gravitational encounter.

Tides

Announcements

Orbits: summary

⊲ Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 6

How does gravity cause tides?

Moon’s gravity pulls harder on near side of Earth than on

far side

Difference in Moons gravitational pull stretches Earth

Tides and Phases

Announcements

Orbits: summary

⊲ Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 7

Size of tides

depends on

phase of

Moon

Tidal Friction

Announcements

Orbits: summary

⊲ Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 8

Tidal friction gradually slows Earth rotation (and makes

Moon get farther from Earth).

Moon once orbited faster (or slower); tidal friction

caused it to lock in synchronous rotation.

How do we experience light?

Announcements

Orbits: summary

Tides

⊲ Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 10

The warmth of sunlight: light is a form of energy

Energy flow is measured in watts: 1 watt = 1 joule/s

How do we experience light?

Announcements

Orbits: summary

Tides

⊲ Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 10

The warmth of sunlight: light is a form of energy

Energy flow is measured in watts: 1 watt = 1 joule/s

One joule in everyday life is approximately:

⊲ Energy required to lift up a small apple one meter

(100 g ≈ 1/9.8 kg)

⊲ Energy released when the apple falls one meter

⊲ The energy released as heat by a person every

1/60th of a second

⊲ Kinetic energy of a 50 kg human moving slowly

(0.2 m/s)

⊲ Kinetic energy of a tennis ball at 23 km/h (14 mph)

How do we experience light?

Announcements

Orbits: summary

Tides

⊲ Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 10

The warmth of sunlight: light is a form of energy

Energy flow is measured in watts: 1 watt = 1 joule/s

White light is made up of different colors

How do we experience light?

Announcements

Orbits: summary

Tides

⊲ Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 10

The warmth of sunlight: light is a form of energy

Energy flow is measured in watts: 1 watt = 1 joule/s

White light is made up of different colors

How do light and matter interact?

Announcements

Orbits: summary

Tides

Experience

⊲ Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 11

Emission

Absorption

Transmission

⊲ Transparent objects transmit light

⊲ Opaque objects block (absorb) light

Reflection or Scattering

Reflection and scattering

Announcements

Orbits: summary

Tides

Experience

Interaction

⊲ Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 12

Mirror reflects

light in a partic-

ular direction

Movie screen reflects light in many direc-

tions

Interaction of Light and Matter

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

⊲ Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 13

Interactions between light and matter determine the

appearance of everything around us

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

⊲ Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 14

Why is a rose red?

The rose absorbs red light.

The rose transmits red light.

The rose emits red light.

The rose reflects red light.

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

⊲ Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 14

Why is a rose red?

The rose absorbs red light.

The rose transmits red light.

The rose emits red light.

The rose reflects red light.

Why Study Light?

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

⊲ Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 15

Astronomy is passive science —

Why Study Light?

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

⊲ Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 15

Astronomy is passive science — observations!

Can only VISIT most nearby celestial objects

Want knowledge of physical properties!

Why Study Light?

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

⊲ Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 15

Astronomy is passive science — observations!

Can only VISIT most nearby celestial objects

Want knowledge of physical properties!

Using light we can determine the following properties:

⊲ Temperature

⊲ Composition

⊲ Velocity

Light as particles

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

⊲ Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 16

Light travels through empty space at a speed of

c = 300, 000 km/s

Olaus Romer (1676) dis-

covered that eclipse tim-

ing depended on distance

of Earth to Jupiter

Implies a speed of light

propagating in a vacuum

Light as particles

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

⊲ Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 16

Light travels through empty space at a speed of

c = 300, 000 km/s

Olaus Romer (1676) dis-

covered that eclipse tim-

ing depended on distance

of Earth to Jupiter

Implies a speed of light

propagating in a vacuum

Galileo tried to mea-

sure speed of light with

lanterns on mountain-

tops!

Light as particles

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

⊲ Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 17

Romer’s drawing

Speed of light in the lab

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

⊲ Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 18

Fizeau and Foucalt (1850) measured speed of light by

bouncing a beam off of a rotating mirror

Mirror moves as light travels

The light returns to its source at a different position

Speed of light in the lab

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

⊲ Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 18

Fizeau and Foucalt (1850) measured speed of light by

bouncing a beam off of a rotating mirror

Mirror moves as light travels

The light returns to its source at a different position

To summarize:

Light has a well-defined speed,

as if it were made of bullets!

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 19

Light is composed of all colors (rainbow).

How and Why?

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 20

Isaac Newton suggested that light was made of tiny

particles called PHOTONS

Attempted to explain spectrum using properties of the

particles

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 21

“Nothing is more

requisite for produc-

ing all the variety of

Colours, and degrees

of Refrangibility than

that the Rays of Light

be Bodies of different

Sizes, the least of

which may take vio-

let the weakest and darkest of the Colours, and be more easily

diverted by refracting Surfaces from the right Course; and the

rest as they are bigger and bigger, may make the stronger and

more lucid colours, blue, green, yellow, and red, and be more

and more difficultly diverted.”

Sir Issac Newton, Opticks

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 22

Young (1801): light has wave-like properties.

Light passing through two narrow slits which resulted in

a pattern of bright and dark bands

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 22

Young (1801): light has wave-like properties.

Light passing through two narrow slits which resulted in

a pattern of bright and dark bands

Light as waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

⊲ Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 22

Young (1801): light has wave-like properties.

Light passing through two narrow slits which resulted in

a pattern of bright and dark bands

Propagation of waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

⊲ Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 23

wavelength: distance between crests

frequency: rate at which crests move past a fixed point

wavelength × frequency = speed

FM radio waves transmit information by changing the

frequency of the waves. Your radio can then create

sound by recognizing these changes in frequency.

Propagation of waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

⊲ Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 23

wavelength: distance between crests

frequency: rate at which crests move past a fixed point

wavelength × frequency = speed

FM radio waves transmit information by changing the

frequency of the waves. Your radio can then create

sound by recognizing these changes in frequency.

Propagation of waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

⊲ Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 24

Material does not move in the direction of wave

propagation!!

Example:

⊲ Bobber in water

⊲ Swimming in ocean

Waves move past the object . . .

Propagation of waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

⊲ Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 24

Material does not move in the direction of wave

propagation!!

Example:

⊲ Bobber in water

⊲ Swimming in ocean

Waves move past the object . . .

What is the medium for light propagation?

Propagation of waves

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

⊲ Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 24

Material does not move in the direction of wave

propagation!!

Example:

⊲ Bobber in water

⊲ Swimming in ocean

Waves move past the object . . .

What is the medium for light propagation?

Luminiferous Aether: a massless vapor that filled the

Universe (19th century) to propagate heat and light

Electromagnetic radiation

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

⊲ EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 25

Electromagnetic waves are waves of energy that travel

through space at the speed of light

Consist of combined electric and magnetic waves that

result when a charged particle accelerates

The acceleration creates a wave with both electric and

magnetic components

Electromagnetic radiation

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

⊲ EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 26

Astronomically important

frequencies range from:

◦ 102 Hz (low) to 1024

Hz (high)

Astronomically important

wavelengths range from:

◦ 108 cm (long) to

10−14 cm (short)

William Herschel and Infrared

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

⊲ Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 27

Circa 1800: used mercury ther-

mometers to measure the en-

ergy in different colors of light

Highest temperature was just

beyond the red part of the spec-

trum

Discovered energy beyond the

visible spectrum: infrared!

Energy and Intensity of Light

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

⊲Energy &Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 28

Energy carried by a photon is proportional to its

frequency

E = hν = hc/λ

Planck’s constant:

h = 6.63× 10−34 Joule-sec

Therefore, the total energy carried by a beam of light (its

intensity) depends both on the number of photons per

second and their frequency

Properties of Light: Summary

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

⊲ Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 29

Particle properties

⊲ Travels in straight lines (bullets)

⊲ “Rays” are parallel far from source

⊲ E = hν

Wave properties

⊲ “Rainbow” spectrum

⊲ Interference

Light is electromagnetic radiation

Wave-Particle Duality: light has both wave-like and

particle-like properties!

Energy and Intensity of Light

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

⊲ Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 30

Energy carried by a photon is proportional to its

frequency

E = hν = hc/λ

Planck’s constant:

h = 6.63× 10−34 Joule-sec

Therefore, the total energy carried by a beam of light (its

intensity) depends both on the number of photons per

second and their frequency

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

⊲ Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 31

Question: Is there an interference pattern if I fired one photon

at at time at the double slits?

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

⊲ Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 31

Question: Is there an interference pattern if I fired one photon

at at time at the double slits? Yes

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

⊲ Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 31

Question: Is there an interference pattern if I fired one photon

at at time at the double slits?

Particle-wave duality

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

⊲ Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 32

The higher the photon energy . . .

the longer its wavelength.

the shorter its wavelength.

energy is independent of wavelength.

Thought question

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

⊲ Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 32

The higher the photon energy . . .

the longer its wavelength.

the shorter its wavelength.

energy is independent of wavelength.

What is the structure of matter?

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

⊲

What is thestructure ofmatter?

Atomic terminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 33

[Atom] [Electron cloud] [Nucleus]

Atomic terminology

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

⊲Atomicterminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 34

Atomic Number = # of protons in nucleus

Atomic Mass Number = # of protons + neutrons

Molecules: consist of two or more atoms (H2O,CO2)

Atomic terminology

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

⊲Atomicterminology

Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 35

Isotope: same # of protons but different # of neutrons.

(4He, 3He)

Phases & Pressure

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

⊲ Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 36

Example: familiar phases (of water)

Solid (ice)

Liquid (water)

Gas (water vapor)

Phases of same material behave differently because of

differences in chemical bonds

Phases & Pressure

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

⊲ Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 36

Example: familiar phases (of water)

Solid (ice)

Liquid (water)

Gas (water vapor)

Phases of same material behave differently because of

differences in chemical bonds Less familiar phase:

Ionized (plasma)

Phases & Pressure

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

⊲ Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 37

Ionization: Stripping of electrons,

changing atoms into plasma

Dissociation: Breaking of molecules

into atoms

Evaporation: Breaking of flexible

chemical bonds, changing liquid into

solid

Melting: Breaking of rigid chemical

bonds, changing solid into liquid

Phases & Pressure

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

⊲ Phases & Pressure

Internal energy

Read: Chap 5 09/25/12 – slide 38

Phase of a substance depends on both temperature and

pressure

Often more than one phase is present

Internal energy

Announcements

Orbits: summary

Tides

Experience

Interaction

Reflect/Scatter

Light/Matter

Thought question

Why Study Light?

Light as particles

Light as particles

Speed of light

Light as waves

Wave propagation

EM Radiation

Infrared

Energy & Intensity

Summary

Intensity

Thought question

What is the structureof matter?

Atomic terminology

Phases & Pressure

⊲ Internal energy

Read: Chap 5 09/25/12 – slide 39

How much energy is stored in atoms?

Electrons in atoms are restricted to particular energy

levels

Internal energy

Read: Chap 5 09/25/12 – slide 40

Energy Level Transitions

The only allowed

changes in en-

ergy are those

corresponding

to a transition

between energy

levels

Internal energy

Read: Chap 5 09/25/12 – slide 40

Energy Level Transitions

Disallowed!

The only allowed

changes in en-

ergy are those

corresponding

to a transition

between energy

levels

Internal energy

Read: Chap 5 09/25/12 – slide 40

Energy Level Transitions

Disallowed! Allowed!

The only allowed

changes in en-

ergy are those

corresponding

to a transition

between energy

levels