Index

U03Mod01 Light as a Wave 1

Unit 03 Electron Configuration

Module 01: Light as a Wave

Based on the PowerPoints By Mr. Kevin Boudreaux, Angelo State Univerisity

Index

U03Mod01 Light as a Wave 2

Module 01: Student Expectations

• Be able to– define the terms wavelength, frequency, and amplitude. – label the parts of a wave.– calculate the wavelength or frequency using the speed

of light equation.– explain interference.– explain diffraction.– explain how we know light behaves like a wave.– state that light behaves as a wave and a particle (dual

wave-particle nature).

Index

U03Mod01 Light as a Wave 3

Light and Matter

• We know that both light and electrons have a dual wave-particle nature.– Some properties are best described by a wave

model while some properties are best described by a particle nature.

Index

U03Mod01 Light as a Wave 4

Electromagnetic Radiation

• Visible light, infrared radiation, ultraviolet light, radio waves, microwaves, X-rays, and gamma (γ) rays are types of electromagnetic (EM) radiation.

• Electromagnetic radiation propagates energy using electric and magnetic fields that are perpendicular to each other.

Index

U03Mod01 Light as a Wave 5

Frequency, Wavelength, and Amplitude

• EM radiation behaves in some ways like ocean waves traveling through water. The wave properties of EM radiation can be described by the following three variables:– Wavelength (λ, lambda) – the distance from one wave peak to

the next (or trough to trough, or corresponding points) (units of length, m, nm)

– Amplitude – the height of the wave measured from the center line (rest position); the intensity or brightness of the light is proportional to the square of the amplitude.

– Frequency (ν, nu) – the number of wave peaks that pass by a given point per unit time (units of cycles per second, 1/second, s-

1, Hz [Hertz])

Index

U03Mod01 Light as a Wave 6

Frequency, Wavelength, and Amplitude

Index

U03Mod01 Light as a Wave 7

The Speed of Light; Relating ν and λ

• In a vacuum, all EM radiation travels at the speed of light, c or 2.99792458x108 m/s.

• Because the speed of light is constant, frequency and wavelength are inversely proportional to each other:

• What is different about each type of EM radiation is its wavelength and frequency (and also its energy [more about this later])

• Visible light extends from wavelengths of 750 nm (red) to 400 nm (violet); “white light” is a combination of all these wavelengths of radiation.

Index

U03Mod01 Light as a Wave 8

The Electromagnetic Spectrum• The colors that we see around us results from an object

absorbing some wavelengths of visible radiation and reflecting others back to our eyes.

• White light from the sun can spread out with a prism to form a continuous spectrum, with no breaks in between the colors:

• Visible light represents only a small portion of the continuum of radiant energy known as the electromagnetic spectrum.– Higher frequency light includes ultraviolet (UV) rays, X-rays, and

gamma rays.– Lower frequency light includes infrared (IR) radiation, microwaves,

and radio waves.

Index

U03Mod01 Light as a Wave 9

The Electromagnetic Spectrum

Index

U03Mod01 Light as a Wave 10

The Electromagnetic Spectrum

What radiation has a frequency of 9.6x1017 Hz? Wavelength of 2.5cm?

Index

U03Mod01 Light as a Wave 11

Examples

1) What frequency of radiation has a wavelength of 495 nm? What type of EM radiation is it?

Index

U03Mod01 Light as a Wave 12

Examples

2) What is the wavelength of electromagnetic radiation that has a frequency of 6.45 x 109 Hz? What type of EM radiation is it?

Index

U03Mod01 Light as a Wave 13

Examples

3) What is the wavelength in nanometers of electromagnetic radiation that has a frequency of 5.099x1014 Hz? What type of EM radiation is it?

Index

U03Mod01 Light as a Wave 14

Wave Properties Evidence

• We know that light and electrons have dual wave-particle nature.

• Waves can undergo certain phenomenon that also occur with light and electrons.

• Some of these phenomenon include– Interference– Diffraction

Index

U03Mod01 Light as a Wave 15

Constructive and Destructive Interference

• Waves can interfere with each other constructively or destructively:

Wave amplitudes add Constructive interference

Wave amplitudes cancel Destructive interference

Index

U03Mod01 Light as a Wave 16

Diffraction• A wave bends around an object that is comparable in size

to its wavelength, producing a new set of waves in a process called diffraction:

• A stream of particles, on the other hand, would either be blocked by the barrier, or sail through the opening without being diffracted:

Index

U03Mod01 Light as a Wave 17

Diffraction• If light strikes a barrier with two slits (with a separation comparable

to the wavelength of the light), the light is diffracted through both slits, producing an interference pattern on the other side. This phenomena would be produced by anything which has wave properties, but not by something that has only particle properties.

Index

U03Mod01 Light as a Wave 18

Wave Interference Simulation

• http://phet.colorado.edu/en/simulation/wave-interference