Light: Electromagnetic Spectrum Ms. Donis

Introduction to electromagnetic waves Electromagnetic radiation is one of the many ways that energy travels in space Examples: X-rays that are used at doctor’s office UV rays from the sun Heat from a burning fire All these examples exhibit wavelike properties

Properties of a wave Trough is the lowest point of the wave Crest is the highest point of the wave Amplitude is the vertical distance between the tip of the crest and the wave’s central axis. Wavelength (in meters) is the distance between two crests or two troughs

Properties of a wave Frequency: the number of full wavelengths that pass a given point every second The SI unit for frequency is Hertz (Hz)= per seconds (1/s) Wavelength and frequency have an inversely proportional relationship. The shorter the wavelength, the higher the frequency The longer the wavelength, the lower the frequency

In Hertz (Hz) or per second (1/s) C = 3.00 x 108 m/s In meters

Concept Check (Work in Groups) For each description, determine if it is true or false. If it is false, rewrite the description with the correct information. True or False: A trough is the highest point on a wave True or False: Frequency and wavelength have an inversely proportional relationship True or False: Frequency is measured in meters per second.

Example 1: A particular wave of electromagnetic radiation has a frequency of 1.5 x 1014 Hz. What is the wavelength of this wave?

Example 2: A laser emits a light with a frequency of 4.74 x 1014 sec-1. What is the wavelength of the light in nm?

Example 3 (Work in Groups) A certain electromagnetic wave has a wavelength of 625 nm. What is the frequency of the wave?

RECAP Properties of waves: Frequency Wavelength: usually expressed in meters, centimeters, or nanometers. Amplitude Equation for the speed of light:

The Electromagnetic Spectrum Electromagnetic waves can be classified into various wavelengths and frequencies, and this classification is known as the electromagnetic (EM) spectrum. The EM spectrum includes multiple types of EM radiation, that only differ by wavelength and frequency. Wavelength and Frequency have an inverse relationship

The Electromagnetic Spectrum Visible light only covers a very small portion of the electromagnetic spectrum. Everything to the left of the visible spectrum (with increasing frequency) is harmful Everything to the right of the visible spectrum, is not As the frequency increases, so does the energy.

Visible light, like the white light found in sunlight or other atifical light, enters the prism and separates into a continous spectrum of colors with a nearly continuous frequency and wavelenght.

Planck’s Theory In 1900, physicist Max Planck did research on blackbodies. Blackbodies are surfaces or objects the absorbs all electromagnetic radiation, and has the ability to emit it.

Why do metal emit different colors when heated? When metals are heated, they emit a glowing light. The temperature at which the metals are heated, causes the metal to absorb energy and then emit that energy in the form of light. https://www.youtube.com/watch?v=lqLlmXmMiFQ https://www.youtube.com/watch?v=XtHtAiUVb7M

Planck’s Theory According to Planck, matter can absorb and emit energy in whole number multiples of the value hv, also known as quanta. Quanta or “quantum” is the minimum amount of energy that can be gained or lost by an atom. h is Planck’s constant= 6.626 x 10-34 J x s v is frequency

Planck’s Theory Planck’s research lead to the discovery of the photon, a particle or quantum of light. Photons can be absorbed or emitted by particles like electrons.

Planck’s Theory As the electron, move up the orbits, it absorbs energy. As it moves down, it releases energy. This energy can be expressed as: Frequency Energy of the photon absorbed or emitted, in Joules (J) Planck’s constant= 6.626 x 10-34 J x s

Example 4: A photon has a frequency of 2.0 x 1024 Hz. What is the energy of this photon?

Example 5: Work in Groups Calculate the energy possessed by a single photon of each of the following types of electromagnetic radiation: 6.32 x 1020 sec-1 9.50 x 10 13 Hz 1.05 x 1016 s-1