The Electromagnetic Spectrum

Properties of Waves

The Famous Double Slit Experiment

The Famous Double Slit Experiment

Light as a Particle

• Isaac Newton (1642-1727) believed light consisted of particles

• Light particles are called the photons

Light Phenomenon

•Photons• have no charge• carry the electromagnetic force (EMF)

• electrons and electricity both interact via the electromagnetic force – this means that photons and electrons can interact.

Is light a particle or a wave?

A. Particle

B. Wave

C. Both a particle and a wave

D. Neither a particle nor a wave

Is light a particle or a wave?

A. Particle

B. Wave

C. Both a particle and a wave

D. Neither a particle nor a wave

The Electromagnetic Spectrum

Low EnergyLong Wavelengths

High EnergyShort Wavelengths

The Electromagnetic Spectrum

Low EnergyLong Wavelengths

High EnergyShort Wavelengths

RedOrangeYellowGreenBlueIndigoViolet

ROY G BIVLow EnergyLong Wavelengths

High EnergyShort Wavelengths

Visible Light

The speed of light is the universal speed limit!

C = λν

Speed of Light, c = 3.00 x 108 m/s

Speed of Light, c = 3.00 x 108 m/s

We could view the speed of light, c, a definition shown as the following:

3.00 x 108 m = 1 s

Speed of Light, c = 3.00 x 108 m/s

3.00 x 108 m = 1 s

The sun is 1.4 x 1011 meters away. How long does it take for the sun light to reach earth in minutes?

1.4 × 1011𝑚 ×1𝑠

3.00 × 108𝑚= 467s

467s ×1𝑚

60𝑠= 7.78𝑚𝑖𝑛𝑢𝑡𝑒𝑠

Try this!

Proportional VS Inversely Proportional

What does proportional and inversely proportional mean?

𝐴 ∝ 𝐵

𝐴 ∝1

𝐶

∝ means proportional

Wavelength Frequency Relationship – In Class Demo

https://phet.colorado.edu/en/simulation/wave-on-a-string

Choose the following options: Oscillate, No End, No Dampening

Wavelength Frequency Relationship – In Class Demo

What happens to the wavelength when the frequency is increased?

It get’s shorter!

Wavelength Frequency Relationship – In Class Demo

What happens to the wavelength when the frequency is decreased?

It gets longer!

Wavelength Frequency Relationship

Are frequency and wavelength proportional or inversely proportional to each other?

Wavelength ↑ Wavelength ↓

Frequency ↓ Frequency ↑

Scenario 2Scenario 1

inversely proportional

Wavelength Frequency Relationship

Are frequency and wavelength proportional or inversely proportional to each other?

𝜆 ∝1

𝜐

• When frequency increases, 1/v gets smaller, and the wavelength decreases

• When frequency decreases, 1/v gets larger, and the wavelength decreases

inversely proportional

• Crest – highest point of a wave

• Trough – lowest point of a wave

• Wavelength (λ) – distance from crest to crest • Units are meters or nanometers; 1x109 nm = 1m

• Frequency (ν) - number of waves to cross a point in 1 second • Units are Hertz (Hz), cycles/sec, or sec-1

• 1 Hz = 1/s

𝑐 = 𝜆 × 𝜐

Math Manipulations

• Wavelength (λ) – distance from crest to crest • Units are meters or nanometers; 1x109 nm = 1m

• Frequency (ν) - number of waves to cross a point in 1 second • Units are Hertz (Hz), cycles/sec, or sec-1

• 1 Hz = 1/s

𝑐

𝜐= 𝜆 ×

𝜐

𝜐

𝑐

𝜐= 𝜆

𝑐

𝜆= 𝜐

𝑐 = 𝜆 × 𝜐

𝑐

𝜆=𝜆

𝜆× 𝜐

Frequency Ranges

Radio Microwave Infrared(IR)

Visible Ultraviolent(UV)

X-Ray Gamma Ray

Wavelength (m) 104 1 10-2 10-5 10-6 10-8 10-10 -10-12

3 x 104 3 x 108 3 x 1010 3 x 1013 3 x 1014 3 x 1016

Calculate the wavelength of yellow light emitted from a sodium lamp if the frequency is

5.10 x 1014 Hz (5.10 x 1014 s-1)

List the known info

c = 3.00 x 1010 cm/s

Frequency (v) = 5.10 x 1014 s-1

List the unknownwavelength (λ) = ? nm

𝑐

𝜐= 𝜆 ×

𝜐

𝜐

𝑐

𝜐= 𝜆

𝑐 = 𝜆 × 𝜐

𝜆 =𝑐

𝜐=

3.0 × 108𝑚/𝑠

5.10 × 1014𝑠−1

= 5.88 × 10−7𝑚

Your Turn

What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1?

List the known infoc = 3.00 x 1010 cm/s

Frequency (v) = 1.50 x 1013 s-1

List the unknownwavelength (λ) = ? nm

𝑐

𝜐= 𝜆 ×

𝜐

𝜐

𝑐

𝜐= 𝜆

𝑐 = 𝜆 × 𝜐

𝜆 =𝑐

𝜐=

3.0 × 108𝑚/𝑠

1.50 × 1013𝑠−1

= 2.0 × 10−5𝑚

Your Turn

What frequency is radiation with a wavelength of 5.00 x 10-6 cm? In what region of the electromagnetic spectrum is this radiation?

List the unknownFrequency (v) = ?

=3.0 × 108𝑚/𝑠

5.00 × 10−6𝑐𝑚

= 6.0 × 1015𝑠−1𝑐

𝜆= 𝜐

𝑐 = 𝜆 × 𝜐

𝑐

𝜆=𝜆

𝜆× 𝜐

𝜐 =𝑐

𝜆

5.00 × 10−6𝑐𝑚1𝑚

100𝑐𝑚= 5.00 × 10−8𝑚

=3.0 × 108𝑚/𝑠

5.00 × 10−8𝑚

List the known infoc = 3.00 x 108 m/swavelength (λ) = 5.00 x 10-6 cm

Light Produced by Atoms in an Excited State

Energy of photon = change of

energy due to relaxation

The energy of the photon released corresponds to a wavelength

If this wavelength is in the visible region, we can see the color of the light.

Each element gives specific wavelengths of light due to the change in energy of the electrons.

Light given off from the atom can be separated using a prism. The lines that result from the separation are called spectral lines.

Each element has its own fingerprint of spectral lines that allows us to identify the element.

Emission Spectra

•Makes it possible to identify the chemical make up of inaccessible substances, such as stars.•Most of our knowledge of the universe comes from

studying the emission spectra of stars.

•Neon

•Argon

The Photoelectric Effect

When light shines on metals, electrons (photoelectrons) are ejected from their surface.

• The light must have enough energy to eject the electron. For instance, in the potassium sample below, the light must have an energy greater than 2.0 eV to eject electrons. This energy threshold is referred to as the work function. Any energy in excess of the energy threshold, increases the kinetic energy of the ejected electron.

Red light will

not eject

electrons!

Photoelectric Effect

The photoelectric effect has practical applications in photoelectrical cells used for solar powered cars, and solar powered calculators.