Unit 8: Light and Optics Chapter 23: The Physical Nature of Light 23.1 Electromagnetic Spectrum 23.2 Interference, Diffraction, and Polarization 23.3 The Dual Nature of Light

Do Now Discussion Questions 5/2/14 Get a copy of notes. We will discuss the question. You do not need to write it down. How are x-rays, sunlight, and microwaves related?

Frequency, Wavelength, and Speed Read - 23A The Electromagnetic Spectrum

Electromagnetic waves If you switch electricity on and off repeatedly, the oscillating electricity makes an electromagnetic wave. This is exactly how radio towers make radio waves.

Electromagnetic spectrum This spectrum includes both visible light and invisible waves: radio wave microwaves infrared light ultraviolet light X-rays gamma rays

Electromagnetic wave speed All electromagnetic waves travel at the same speed in a vacuum, the speed of light—3 × 108 m/s. When moving through a material, the frequency of light stays the same. END of 23A - Page 1

Electromagnetic waves A wave of oscillating electric and magnetic fields that moves at the speed of light.

Energy of electromagnetic waves We classify the energy of electromagnetic waves by comparing it to the energy it takes to remove an electron from an atom. Classified as High or Low 23.2 Organizer

Low-energy electromagnetic waves Low energy waves, like visible light, do not have enough energy to break most chemical bonds: Radio waves are the lowest-frequency waves (km to 30cm). Microwaves range in length from 1 mm to 30 cm. Infrared waves include wavelengths from 1 mm to about 700 nm. Visible light include wavelengths from 700 nm to 400nm. 23.2 Organizer

Frequencies and wavelengths of light Since color is related to energy, there is a direct relationship between color (energy) and frequency and an inverse (indirectly) relationship between color (energy) and wavelength. 23.2 Organizer

High-energy electromagnetic waves has enough energy to remove electrons and to break chemical bonds. Ultraviolet light 10nm to 400nm. X-rays 10nm to 0.001nm. Gamma rays extremely small less than ten-trillionths of a meter and can strip the innermost electrons out of an atom. 23.2 Organizer

Unit 8: Light and Optics Chapter 23: The Physical Nature of Light 23.1 Electromagnetic Spectrum 23.2 Interference, Diffraction, and Polarization 23.3 The Dual Nature of Light

Young’s double slit experiment In 1807, Thomas Young proved light was a wave when he showed that two beams of light could interfere with each other.

Diffraction gratings A diffraction grating is a series of thin parallel grooves on a piece of glass or plastic. When light goes through a diffraction grating, each groove scatters the light so the grating acts like many parallel slits.

Spectrometers A spectrometer is a calibrated diffraction grating used to create a spectrum. The spectrometer has a scale that allows you to read different wavelengths of light directly from the pattern of light made by the grating.

Polarization The orientation of light is called its polarization. Only transverse waves can have polarization.

Polarizers A polarizer is a material that allows light of only one polarization to pass through it. Light with a single polarization is called polarized light.

Applications of polarization Polarized sunglasses reduce glare because they selectively absorb light with horizontal polarization while letting other light through.

Applications of polarization Images on a LCD (liquid crystal display)are made using polarized light. Each liquid crystal window can be electronically controlled to act like a polarizer, or not.

Energy, color and light The lowest-energy photons we can see are the ones that appear red to our eyes. White light is a mixture of photons with a range of energy.

Energy and intensity of light If glow-in-the-dark plastic is exposed to light, it stores some energy and releases the energy later by giving off light. The process of releasing stored light energy is called photoluminescence. Glow-in-the-dark plastic demonstrates that a single atom only absorbs a single photon at a time.

How 3-D Movies Work Cinematographers, ophthalmologists, optical engineers, and computer graphic designers all play a role in the development of modern 3- D movie technology. To create the illusion of three- dimensions on a flat screen, each eye must receive its own separate image of the movie, from a slightly different perspective, mimicking the way your eyes take in a real three- dimensional scene.