Objectives

I can calculate wavelength, frequency or energy of light.

I can explain the emission spectrum of an element.

warmup

xy

4

equation #1

equation #2

xy 4

1. In equation #1, if the value of x increases, then y will ____________

2. In equation #2, if the value of x increases, then y will _____________

3. Which equation is a direct proportion? ____________

4. Which equation is an inverse proportion? ____________

5. In equation #3, y is ______________ proportional to x. (directly, inversely)

6. In equation #3, y is ______________ proportional to z. (directly, inversely)equation #3 z

xy

How do Neon lights work?

First we need to know what light is and how to quantify properties of light:

frequency wavelength energy

Electromagnetic Waves Light is an electromagnetic wave.

Wave simulation

Frequency of a wave (f ) is the number of wave cycles that pass a given point in one second: cycles per second or Hertz (Hz)

1. label wavelength2. label crest, 3. label trough4. label amplitude

Electromagnetic radiation includes radio waves, radar, microwaves, visible light, infrared waves, ultraviolet light, x-rays, and gamma rays.

Electromagnetic Waves

Key Point! For every type of electromagnetic wave, the speed is the same.

Electromagnetic Waves

For every electromagnetic wave, if you multiply the frequency by the wavelength you always get the speed of light!Speed of Light = (frequency)(wavelength)

fc

Frequency and Wavelength formula

/s f = frequency λ (lamda) = wavelength

formula:

frequency:

wavelength:

fc

Frequency and Wavelength formula

velocity of a light wave: velocity of a light wave: c = 3.0 x 108 m/s

f = frequency λ (lamda) = wavelength

speed of light:

frequency:

wavelength:

c

f

f

c

fc

fc

c

f

If the wavelength gets decreases, then frequency will ________.

A. decreaseB. increaseC. remain constant

cf

Therefore wavelength and frequency are ______________.

A. directly proportionalB. inversely proportionalC. not related

cf

Example 1: Calculate wavelength

Bob FM broadcasts music at a frequency of 103.5 MHz = 103.5 x 106 Hz. What is the wavelength of a Bob FM wave?

fc

c

f

Example 1: Calculate wavelength

Bob FM broadcasts music at a frequency of 103.5 MHz = 103.5 x 106 Hz. What is the wavelength of a Bob FM wave?

fc

mHz

m

f

c 90.2

105.103

sec/1000.36

8

Example 2: Calculate frequency

A DVD player uses a red laser with a wavelength of 6.5 x 10-7 m. What is the frequency of this light?

fc

Example 2: Calculate frequency

A DVD player uses a red laser with a wavelength of 6.5 x 10-7 m. What is the frequency of this light?

Hzm

mcf 14

7

8

106.4105.6

sec/1000.3

c

ffc

“Color” of light depends on the wavelength, the shorter the wavelength the higher the frequency.

The shorter the wavelength, the higher the energy.

sketch an electromagnetic wave getting shorter and shorter

Which wave has the higher energy per photon?

A. Wave AB. Wave B

[Default][MC Any][MC All]

When light reacts with matter it acts as particles called a photons.

A photon is a quanta of energy that is carried by the light wave.

Light is particles of energy!!!

The energy carried by a photon can be calculated if we know the frequency or the wavelength of the photon

Energy = h x f h = Plank’s constant (6.63 x 10-34) f = frequency

since f= c / … Energy = h x c

Energy depends on the ‘color’

Energy = h x f

The higher the frequency, the higher the energy!

= Directly Proportional

h = Plank’s constant (6.63 x 10-34)

How do Neon lights work?

Energy = h x c = h x f λ

The shorter the wavelength, the higher the energy! = inversely proportional

How do Neon lights work?

To calculate energy of a photon given frequency

What is the energy of a photon of microwave radiation with a frequency of 3.20x1011 Hz?

ans: 2.21E-22 J

To calculate energy of a photon given its wavelength

What is the energy of an x-ray photon that has a wavelength of 0.05 nanometer. note: 1nanometer (nm) = 1x10-9 m

1.99 x10 -16 J

Electromagnetic Spectrum

exit quiz

Einstein proposed that light could be described as a quanta of energy and behave like particles.

Einstein proved this phenomenon by explaining the photoelectric effect.

This effect occurs when light hits the surface of a metal, and electrons are ejected.

How do Neon lights work?

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

When elements in the gaseous state are electrically stimulated, they emit a light of a specific wavelength, or color.

Every element emits a different colored light.

Neon = orange redXenon = blueArgon = lavender

How do Neon lights work?

So where exactly does the neon light come from?

As electrons gain energy, they become excited and move into high energy levels around the atom.

How do Neon lights work?

When those electrons drop back down to the original energy level, the energy is released as a photon of light.

How do Neon lights work?

http://phet.colorado.edu/en/simulation/discharge-lamps

The specific color that each element emits is called its atomic emission spectrum.

This spectrum can go outside of the visible light range.

How do Neon lights work?

Concepts