Light Intro!

Light Intro!

Light Discussion Questions What is light? Is light matter? Are there different kinds of light? If so, what are they? What is the same about those kinds of light? What is the difference

between those kinds of light? You may have heard about light waves. What other waves do you know

about? What do all these waves have in common? What is different about them? You may have heard of the speed of light; It’s pretty darned fast. Do

different kinds of light travel at the same speed or different speeds? What are some questions about light that you have? List them on your

index card.

Visible part of EM SPectrum

PRISM

Slit

Ray of

White Light

Waves 1/33,000” long

Waves 1/70,000” long

RedOrangeYellowGreenBlueIndigoViolet

400 nm – 700 nm

IMPORTANT LIGHT EQUATION #1

Frequency & wavelength are inversely proportional

c = c: speed of light (2.998 108 m/s): wavelength (m, nm, etc.): frequency (Hz or s-1)

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

1) What wavelength of light has a frequency of 5.4 x 106 Hz?

What type of light is it?

2) What frequencyof light has a wavelength of 2.2m?What type of light is it?

3) What frequency of light has a wavelength of 7.0 x 10-7m?What type of light is it?

4) What wavelength of light has a frequency of 9.7 x 1015Hz?What type of light is it?

Let’s talk about EnergyActivity break

IMPORTANT LIGHT EQUATION #2

E: energy (J, joules)h: Planck’s constant (6.6262 10-34 J·s): frequency (Hz)

E = h

• The energy of a photon is proportional to its frequency.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Electromagnetic Radiation = PHOTONS

Light as a wave

Light as a stream of energy(packets of photons)

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325

Red and Blue Light

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325

Photons - particle of light that carries a quantum of energy

1)What is the energy of a light wave with a frequency of 4.03 x 1011 Hz? What type of light is it?

2) What is the frequency of a light wave with an energy of 6.0 x 10-11 J? What type of light is it?

1)What is the frequency of a light wave with an energy of 1.33 x 10-20 J? What type of light is it?

Today is Monday, 3/18Light Equations 1 & 2Trade & Talkx2 examples of combined Light EquationsTomorrow’s infoPhotons!!Absorption / Emission

I CAN…solve for any variable in the combined light

equationExplain how light acts as a particle (photon) and

also has wave propertiesexplain how we perceive frequency and

amplitudeunderstand how energy is absorbed and emitted

as lightidentify different frequency types of light

Example problem using BOTH Equations… Find the energy of a photon with a wavelength

of 1.0 x 10-3 nm.

GIVEN:h = 6.626 x 10-34 J sc = 3.00 x 108 m/s = ?E = ? = 1.0 x 10-3 nm = ???? m

WORK: = c = 3.00 108 m/s 1.0 x 10-12 m = 3.0 x 1020 s-1

E = hv

c = λv

E = (6.626 x 10-34 J s)(3.0 x 1020s-1)E = 2.0 x 10-13 J

Example problem using BOTH Equations… Find the wavelength of a photon with an energy

of ： 6.2 x 10-10 J.

GIVEN:h = 6.626 x 10-34 J sc = 2.998 x 108 m/s = ? = ?E = 6.2 x 10-10 J

WORK: = c = 6.2 x 10-10 J 6.626 x 10-34 m = 9.356 x 1023 s-1

E = hv

c = λv

λ = 2.998 x 108 m/s 9.356 x 1023 s-1

λ = 3.20 x 10-16 m

Energy of Waves – It takes more energy to travel at a

higher frequency…Low frequency

High frequency, short wavelength

Amplitude

Amplitude

Low frequency,long wavelength

short wavelength

Electromagnetic Radiation = PHOTONS

Light as a wave

Light as a stream of energy(packets of photons)

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325

Vocabulary of a Wave

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 324

A

?

c = speed of light = 2.998 x 10 8 m/s(really fast, true for every kind of light!)

Wavelength (m or nm)

FREQUENCY (HZ OR S-1)

Amplitude (m)

PhotonsAmplitude – The ‘height’ of a wave; We perceive

it as intensityPhoton

a particle light that carries a quantum of energy with the lowest detectable amplitude

More photons means more intensity!Different photons have different energies

Red and Blue Light

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325

Photons - particle of light that carries a quantum of energy

Absorption / EmissionEnergy absorption – Energy is absorbed into an

atom, exciting an electron from a lower energy level to a higher energy level

Energy emission – Energy is released as a light photon when the electron relaxes back to it’s ground state (or lowest energy level)

Bohr model of the atom explains how this works

Bohr Model of Hydrogen

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 331

Nucleus

Possible electron orbits

ee

Bohr Model of Atom

The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.

http://en.wikipedia.org/wiki/Category:Chemistry

Increasing energyof orbitsn = 1

n = 2

n = 3

A photon is emittedwith energy E = hv

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Continuous vs. Quantized Energy

Ene

rgy

A BZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330

continuous quantized

White light Colored light

,k

Pre-Lab!Flame test lab tomorrowYou will be testing the type of light emission for

different metal cationsIt’s super fun!Then you will quantify (code for calculate..) the

emissions!

Types of A / ETypes of energy absorption:

Electricity (electric energy)Photons (light energy) Infrared (heat energy)

Some types of light energy emission:Fluoresence via UV absorption (demo)Infrared (demo)Visible – different colors (demo) Incandescenct lights (demo)Fluoresenct lights

Types of absorptionElectric energy – electricity, this is how your light

bulbs get the energy to emit light energy in the form of photons

Infrared energy – heat, this is how you will get the metal cations in lab tomorrow to emit light energy

Photons – light energy can be absorbed and immediately emitted by materials to be perceived as a certain colorFor example, my green shirt absorbs all types of

photons but green photons, it immediately re-emits and therefore you and I perceive the shirt to be green

Types of EmissionFluoresence – fluoresence happens when an atom

absorbs a high energy light photon and emits a lower energy photon i.e. When UV light is absorbed and visible light is

emitted!Infrared – heat lamp emits both infrared photons and

visible light photons, which has higher energy?Visible – Many metal cations absorb and emit visible

light photonsWhat about the ones that don’t, are they emitting

anything?