Unit2Day1-VandenBout Wednesday, September 18, 2013 4:13 PM Vanden - - PDF document

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Unit2Day1-VandenBout Wednesday, September 18, 2013 4:13 PM Vanden Bout/LaBrake/Crawford CH301 Why should I wear sunscreen? ELECTROMAGNETIC RADIATION UNIT 2 Day 1 CH301 Vanden Bout/LaBrake Fall 2013 Important Information EXAM GRADES WILL

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CH301 Vanden Bout/LaBrake Fall 2013

Vanden Bout/LaBrake/Crawford CH301 Why should I wear sunscreen? ELECTROMAGNETIC RADIATION UNIT 2 Day 1

CH301 Vanden Bout/LaBrake Spring 2013

Important Information

EXAM GRADES WILL BE POSTED By SATURDAY MORNING LM12 and LM13 due Tue 9AM HW4 due Tue 9AM LAUDE LM LECTURE 1 – NO POINTs EXTRA

Unit2Day1-VandenBout

Wednesday, September 18, 2013 4:13 PM Unit2Day1-VandenBout Page 1

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CH301 Vanden Bout/LaBrake Fall 2013

What are we going to learn today? −Electromagnetic Radiation

Understand light as an electromagnetic wave
Understand the relationship between

frequency, wavelength, and the speed of light

−Light as Energy

Understand how light interacts with electrons
Explain the basic principles of the photoelectric

effect

Recognize that light is related to frequency
Explain the concept of a photon

CH301 Vanden Bout/LaBrake Fall 2013

What is “Light”?

Chemists use the word “light” to generally refer to electromagnetic radiation

Electro-Magnetic Wave

Oscillating Electric and Magnetic Field

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CH301 Vanden Bout/LaBrake Fall 2013

Oscillating Electric and Magnetic Field

CH301 Vanden Bout/LaBrake Fall 2013

What is an Electric Field?

Electric Fields surround charged particles

(and time varying magnetic fields)

Cause charge particles to feel a force
A fairly simply field exists between to

plates of opposite electrical charge

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CH301 Vanden Bout/LaBrake Fall 2013

POLLING: CLICKER QUESTION 1

If I place an electron between these two plates it will feel a force in what direction?

A. Left
B. Right
C. Up
D. Down
E. None
++++++++++++++++++

e-

CH301 Vanden Bout/LaBrake Fall 2013

E-Field from Light

The field is “oscillating”

http://www.enzim.hu/~szia/cddemo/edemo2.htm

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CH301 Vanden Bout/LaBrake Fall 2013

POLLING: CLICKER QUESTION 2

If I place an electron in the presence of an

scillating electric field the electron will?
A. Left
B. Right
C. Up
D. Down
E. Oscillate

e-

CH301 Vanden Bout/LaBrake Fall 2013

Describing the wave

Distance between the peaks is the wavelength It really is a “distance”

If I am in one place, “how often” do the peaks pass? It depends on the speed and the wavelength

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CH301 Vanden Bout/LaBrake Fall 2013

3 key parameters for a wave

Wavelength Distance between peaks. Λ Speed (of light) The speed of light (in a vacuum) is constant All light waves travel at the same speed c = 2.998 x 108 m s-1 Frequency The time it takes between two peaks n = c/λ (distance s-1/distance) = s-1 (Hz)

CH301 Vanden Bout/LaBrake Fall 2013

Key Relationship

You can now do most of HW 04

Wavelengths of Light

We typically classify light by wavelength But frequency works equally well Unit2Day1-VandenBout Page 6

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CH301 Vanden Bout/LaBrake Fall 2013

We typically classify light by wavelength But frequency works equally well

CH301 Vanden Bout/LaBrake Fall 2013

POLLING: CLICKER QUESTION 3

Light and Electrons

Everything has electrons In metals those electrons can move (conductor)

What will happen if we shine light on a piece of metal?

A. The electrons will do nothing
B. The electrons will oscillate back and forth
C. The electrons will feel a force but not move
D. The electrons will turn into protons

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CH301 Vanden Bout/LaBrake Fall 2013

Light and Electrons

POLLING: CLICKER QUESTION 4

What will happen if we shine brighter light? Bright light = Bigger Amplitude

CH301 Vanden Bout/LaBrake Fall 2013

Light and Electrons

POLLING: CLICKER QUESTION 4

What will happen if we shine brighter light? Bright light = Bigger Amplitude

A. they will oscillate faster
B. they will oscillate with a bigger amplitude
C. more of them will oscillate
D. more of them will oscillate faster

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CH301 Vanden Bout/LaBrake Fall 2013

Let’s Do an Experiment

Light + Metal Virtual Demo

http://phet.colorado.edu/en/simulation/photoelectric

Use one laptop per group and work together on the activity:

CH301 Vanden Bout/LaBrake Fall 2013

Let’s Do a Virtual Experiment Using Photoelectric Effect Simulator Let’s Do an Experiment

Summarize results of experiment:

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CH301 Vanden Bout/LaBrake Fall 2013

’

Summarize results of experiment:

CH301 Vanden Bout/LaBrake Fall 2013

Threshold Frequency

A whole new idea about Energy

The energy of the light is proportional to the frequency The energy appears to come in “packets” or “photons” One photon interacts with one electron

’

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CH301 Vanden Bout/LaBrake Fall 2013

The energy appears to come in “packets” or “photons” One photon interacts with one electron

h is Planck’s Constant

CH301 Vanden Bout/LaBrake Fall 2013

The work function, Φ, is the minimum E need to eject and electron It is different for different metals

CH301 Vanden Bout/LaBrake Fall 2013

If an electron is ejected from the metal surface, where does the energy of the photon go?

a)Over coming potential energy holding e- in metal b)Into the KE of the electron c)Carried away with reflected light d)Heat e)Both a) & b)

POLLING: CLICKER QUESTION 5

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CH301 Vanden Bout/LaBrake Fall 2013

CLASSIC ENERGY DIAGRAM and POTENTIAL ENERGY WELL

CH301 Vanden Bout/LaBrake Fall 2013

Which of these types of light has the highest energy photons ?

A. “Green” Light (540 nm or 5.4 x 10-7 m)
B. “Red” Light (650 nm or 6.5 x 10-7 m)
C. Radio waves (100 m)
D. X-rays (0.5 nm or 5 x 10-10 m)
E. Infrared (3 mm or 3 x 10-6 m)

POLLING: CLICKER QUESTION 6

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CH301 Vanden Bout/LaBrake Fall 2013

Quick Review of DNA

CH301 Vanden Bout/LaBrake Fall 2013

Why Should I wear Sunscreen? TYPES of DNA DAMAGE

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CH301 Vanden Bout/LaBrake Fall 2013

Why Should you wear Sunscreen?

AVOBENZONE – common active ingredient, UVmax 357 nm Zinc Oxide – reflects UV light

CH301 Vanden Bout/LaBrake Fall 2013

What Did We Learn Today?

Light is a wave with a frequency, speed and wavelength The energy of light is related to the frequency in a way that light seems like a particle (one photon affects one electron) THIS ALLOWS US TO USE LIGHT TO PROBE THE ENERGY OF ELECTRONS IN MATTER

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CH302 Vanden Bout/LaBrake Fall 2012

Learning Outcomes

Understand and perform quantitative calculations based on the relationship between wavelength, energy and the speed of light. Define wavelength, frequency, and energy of a photon. Understand, identify, and rank the different types of light radiation. Describe the photoelectric effect and relate the energy of a photon, the work function and the kinetic energy of the electrons, and describe the effect of the intensity and the energy of the light. Students should understand atomic absorption and emission spectra contain discrete, very sharp lines from transition of electrons between discrete energy levels. Apply the Rydberg formula to predict then energy of transitions between two n levels in the hydrogen atom.

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