Electromagnetic Spectrum and Light Chapter 18

Electromagnetic Waves Transverse Waves Transverse Waves Consist of constantly changing fields Consist of constantly changing fields electric field – space that exerts electric forces on charged particles magnetic field – space that produces magnetic forces

Electromagnetic Waves… Are produced when an electric charge vibrates or accelerates. Are produced when an electric charge vibrates or accelerates. Can travel without a medium. They can travel through a vacuum, empty space, or matter. Can travel without a medium. They can travel through a vacuum, empty space, or matter.

Speed of Light *In a vacuum, the speed of light is 3.00 x 10 8 m/s. **All electromagnetic waves will travel at this speed in a vacuum, but they will differ in wavelength and frequency!

Use the formula for Wave Speed… to calculate the varying wavelengths and frequencies. to calculate the varying wavelengths and frequencies. Wave speed = wavelength x frequency Wave speed = wavelength x frequency

Is electromagnetic radiation a wave of a particle? Travels like a wave with interference Travels like a wave with interference Travels in a straight line and casts shadows like a particle Travels in a straight line and casts shadows like a particle

Photons The packets of energy that make up electromagnetic radiation The greater the frequency the wave has, the more energy each of its photons has.The packets of energy that make up electromagnetic radiation The greater the frequency the wave has, the more energy each of its photons has.

Photoelectric Effect Blue light has a higher frequency than red light, so blue light photons have more energy. Blue light has a higher frequency than red light, so blue light photons have more energy. Blue light has photons that have enough energy to cause electrons to be emitted from a metal surface Blue light has photons that have enough energy to cause electrons to be emitted from a metal surface The emission of electrons from the metal surface is the photoelectric effect The emission of electrons from the metal surface is the photoelectric effect

Intensity The rate at which a wave’s energy flows through a given unit of area The rate at which a wave’s energy flows through a given unit of area Brightness of the light Brightness of the light The intensity of light decreases as photons travel farther from the source of the light. The intensity of light decreases as photons travel farther from the source of the light. Example: Spray Paint Example: Spray Paint

Electromagnetic Spectrum Shows the frequencies of electromagnetic radiation increasing from left to right Shows the frequencies of electromagnetic radiation increasing from left to right The spectrum goes from red to violet: anything beyond the red band is called infrared radiation The spectrum goes from red to violet: anything beyond the red band is called infrared radiation

Parts of the EM Spectrum Visible light is the only part that of the spectrum that you can see. Visible light is the only part that of the spectrum that you can see. The parts of the spectrum include radio waves, infrared waves, visible light, ultraviolet rays, x-rays, and gamma rays. The parts of the spectrum include radio waves, infrared waves, visible light, ultraviolet rays, x-rays, and gamma rays.

Radio Waves Used in radio, tv, microwave ovens, and radars Used in radio, tv, microwave ovens, and radars Longest wavelength and lowest frequency Longest wavelength and lowest frequency Amplitude modulation (AM) – the amplitude of the wave is varied Amplitude modulation (AM) – the amplitude of the wave is varied Frequency modulation (FM) – the Frequency modulation (FM) – the frequency of the wave is varied

Infrared Rays Have higher frequencies than radio waves, but lower than red light Have higher frequencies than radio waves, but lower than red light Used as a source of heat (restaurants and zoos) Used as a source of heat (restaurants and zoos) Thermographs – color-coded Thermographs – color-coded pictures that show variations in temperature

Visible Light The light that you can see with the human eye The light that you can see with the human eye Each wavelength in the visible spectrum corresponds with a frequency and has a particular color. Each wavelength in the visible spectrum corresponds with a frequency and has a particular color. ROY G BIV ROY G BIV

Ultraviolet Rays Has a higher frequency than violet light Has a higher frequency than violet light Used in medicine and agriculture Used in medicine and agriculture Moderate exposure helps your skin produce vitamin D Moderate exposure helps your skin produce vitamin D Used to kill microorganisms Used to kill microorganisms and help plants grow in a and help plants grow in a nursery during winter nursery during winter

X-Rays Used in medicine, industry, and transportation to make pictures of the inside of solid objects Used in medicine, industry, and transportation to make pictures of the inside of solid objects Too much exposure can kill or damage the living tissue Too much exposure can kill or damage the living tissue

Gamma Rays Have the shortest wavelength and the highest frequency Have the shortest wavelength and the highest frequency Have the most energy and the greatest penetrating ability Have the most energy and the greatest penetrating ability used in the medical field to kill cancer cells and make pictures of the brain used in the medical field to kill cancer cells and make pictures of the brain Also used in industry as Also used in industry as inspection tools

Without Light Nothing is Visible…. When you look at objects, what you are seeing is light. When you look at objects, what you are seeing is light. The behavior of light is affected by the material that it strikes. The behavior of light is affected by the material that it strikes.

Transparent Allows most of the light to pass through Allows most of the light to pass through You can see clearly through it You can see clearly through it Examples: glass, water Examples: glass, water

Translucent Scatters light that passes through it Scatters light that passes through it You can see through it, but not clearly You can see through it, but not clearly Example: Frosted glass Example: Frosted glass

Opaque Absorbs or reflects all of the light that strikes it Absorbs or reflects all of the light that strikes it You can’t see through it You can’t see through it Examples: Wood, Metal Examples: Wood, Metal

When light strikes a medium, it is either reflected, absorbed, or transmitted.

Reflection An image is formed from waves that bounce off of a material’s surface An image is formed from waves that bounce off of a material’s surface 1. Regular Reflection: Image formed is clearly defined & looks exactly like the object. Example: mirror 2. Diffuse Reflection: Light scatters in many different directions due to an irregular surface.

If light is transmitted it can be…. Refracted: Bending of light from one medium to another Ex: straw in a cup Refracted: Bending of light from one medium to another Ex: straw in a cup mirage – false or distorted image Polarized: consists of 2 filters that block horizontal and vertical waves. Polarized: consists of 2 filters that block horizontal and vertical waves. Ex. Sunglasses use a vertical filter to block vertical filter to block horizontal light horizontal light

If light is transmitted it can be…. Scattered: light is redirected Scattered: light is redirected when it passes through a medium when it passes through a medium Ex: Sunrise and Sunset – red and orange light is what makes it to your eyes makes it to your eyes

Prism Material that diffracts white light into a color spectrum of light Dispersion – process of white light separating into colors Ex. Rainbow

Primary colors of light Red Blue Green All 3 together produce WHITE light

Secondary colors of light Cyan Yellow Magenta Any 2 colors of light that combine to produce white light are complementary colors.

Pigments Material that absorb some colors of light and reflect the other colors. Material that absorb some colors of light and reflect the other colors. Examples: Paint, ink, pictures, and dye Examples: Paint, ink, pictures, and dye

Primary colors of PIGMENTS Cyan Yellow Magenta All 3 together produce BLACK pigment Any 2 pigments that form black pigments are complementary pigments

Sources of Light Incandescent- Heats a filament until it glows Ex. Typical light bulb

Sources of Light 2. Glowing phosphorus – a phosphor is steadily emitting photons Ex. Used in schools, hospitals, and offices

Sources of Light 3. Laser - Beam of electrons

Sources of Light 4. Neon – electrons move through a gas inside a glass tube Ex. signs

Sources of Light 5. Sodium-vapor Light - Contains neon and sodium metal gives off a yellow tint Ex. Street lights

Sources of Light 6. Tungsten-Halogen Light – similar to an incandescent light, but contains halogen gas Ex. Lamps & headlights