 EM waves are transverse waves that have changing electric fields and changing magnetic fields  Carry energy from place to place  They travel differently than mechanical waves  Are produced differently than mechanical waves

 When an electric charge vibrates, the electric field around it changes creating a changing magnetic field.

 The magnetic and electric fields create each other again and again.

 An EM wave travels in all directions. The figure only shows a wave traveling in one direction.

 The electric and magnetic fields vibrate at right angles to the direction the wave travels so it is a transverse wave.

 Summary- EM waves are produced when an electric charge vibrates or accelerates. The electric and magnetic fields regenerate each other and travel in the form of a wave.  IMPORTANT: EM waves do not need a medium to travel through

 All matter contains charged particles that are always moving; therefore, all objects emit EM waves.  The intensity of light decreases as photons travel farther from the source

 All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

 EM waves usually travel slowest in solids and fastest in gases. MaterialSpeed (km/s) Vacuum300,000 Air<300,000 Water226,000 Glass200,000 Diamond124,000

 Wavelength= distance from crest to crest.  Frequency= number of wavelengths that pass a given point in 1 s.  As frequency increases, wavelength becomes smaller.

 Electromagnetic radiation behaves sometimes like a wave and sometimes like a particle

 In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected.

 Whether or not electrons were ejected depended upon frequency not the amplitude of the light! Remember energy depends on amplitude.

 Years later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves.

 Electrons fired at two slits actually form an interference pattern similar to patterns made by waves

Electromagnetic Waves How they are formed Kind of waveSometimes behave as

Electromagnetic Waves How they are formed Waves made by vibrating electric charges that can travel through space where there is no matter Kind of wave Transverse with alternating electric and magnetic fields Sometimes behave as Waves or as Particles (photons)

 1. What produces EM waves?  2. How fast does light travel in a vacuum?  3. What makes EM waves different from one another?  4. Explain how light behaves like a stream of particles.  5. What happens to the intensity of light as photons move away from the light source?

 The full range of frequencies of electromagnetic radiation is called the electromagnetic spectrum.

 Different parts interact with matter in different ways.

 The full range of frequencies of electromagnetic radiation is called the electromagnetic spectrum.  Different parts interact with matter in different ways.  The ones humans can see are called visible light, a small part of the whole spectrum.

 Used in radio, television, microwaves and radar ◦ Radio broadcasting- ◦ voice converted to electrical signal that are coded onto a radio wave ◦ Amplitude Modulation- (AM)varies the amplitude ◦ Frequency Modulation – (FM) varies the frequency ◦ Your radio receives it, decodes it, and changes it back into a wave that you can hear

◦ Television  Radio waves carry information for pictures  Signals are received by an antenna  Location and weather can affect the signal  Satellite TV- broadcast sent to satellite, then transmitted back to earth  Fun fact- Radiation Control for Health and Safety Act of required TV recievers must not emit radiation above 0.5 milliroentgen per hour  X-ray emissions come from components of the TV that operate at thousands of volts and can generate x-rays

 MRI  MRI was developed in the 1980s to use radio waves to diagnose illnesses with a strong magnet and a radio wave emitter and a receiver. Protons in H atoms of the body act like magnets lining up with the field. This releases energy which the receiver detects and creates a map of the body’s tissues.

 MRI

 Radar ◦ Radio Detection and Ranging ◦ Uses short bursts of radio waves ◦ Waves reflect off of objects ◦ Returning waves are picked up by a receiver  Police Radar ◦ Uses the Doppler Effect ◦ Radio waves sent from police car ◦ The higher the frequency the returning wave is, the faster the car is going ◦ Computer calculates the speed of the car based on the frequency of wave

 Microwaves have wavelengths less than 30 cm - higher frequency & shorter wavelength than a radio wave  Cell phones and satellites use microwaves between 1 cm & 20 cm for communication.  In microwave ovens, a vibrating electric field causes water molecules to rotate billions of times per second causing friction, creating TE which heats the food.

 EM with wavelengths between 1mm & 750 billionths of a meter.  Used daily in remote controls, to read CD- ROMs  Every objects gives off infrared waves; hotter objects give off more than cooler ones.  Fun Fact- Satellites can ID types of plants growing in a region with infrared detectors

 tornado infrared tornado infrared

 Range of EM humans can see from 750 billionths to 00 billionths of a meter.  You see different wavelengths as colors. ◦ Blue has shortest ◦ Red is the longest ◦ Light looks white if all colors are present

 EM waves with wavelengths from about 400 billionths to 10 billionths of a meter.  Have enough energy to enter skin cells ◦ Longer wavelengths – UVA ◦ Shorter wavelengths – UVB rays ◦ Both can cause skin cancer

 Helps body make vitamin D for healthy bones and teeth  Used to sterilize medical supplies & equip  Detectives use fluorescent powder (absorbs UV & glows) to find fingerprints

In order of increasing frequency and decreasing wavelength, the EM spectrum consists of: very long wave radio, used for communication with submarines; long, medium and short wave radio (used for AM broadcasting); FM radio, television and radar; infra-red (heat) radiation, which is recorded in the Earth photographs taken by survey satellites; visible light; ultraviolet light, which, while invisible, stimulates fluorescence in some materials; x rays & gamma rays used in medicine and released in radioactive decay

 km above earth  Molecule of 3 O atoms  Absorbs Sun’s harmful UV rays  Ozone layer decreasing due to CFCs in AC, refrigerators, & cleaning fluids

 And other life on Earth if the ozone layer is destroyed?  phet molecules and light phet molecules and light

 EM waves with shortest wavelength & highest frequency  High Energy- go through skin & muscle  High level exposure causes cancer

 EM with wavelengths shorter than 10 trillionths of a meter.  Highest energy, can travel through several centimeters of lead.  Both can be used in radiation therapy to kill diseased cells.  The composite image shows the all sky gamma ray background.

 A. Gamma rays are low frequency waves.  B. X rays are high-energy waves.  C. Gamma rays are used to treat diseases.

F Fill in the boxes with the waves of the EM spectrum.

 phet simulation molecules and light phet simulation molecules and light

Transparent- a material you can see through clearly Translucent-a material that scatters light Opaque- a material that absorbs or reflects all light

 When light strikes a new medium it can be ◦ Reflected ◦ Absorbed ◦ Transmitted

 Image- copy of an object formed by reflected or refracted waves of light ◦ Regular reflection- when parallel light waves strike a surface and reflect all in the same direction ◦ Diffuse reflection – parallel light waves strike a rough uneven surface and reflect in different directions

 A reflection produced by a smooth surface.

 Reflection from a rough surface.

When a wave crosses a boundary between Medium 1 and Medium 2, the wave changes direction because it changes velocity.  Frequency remains constant.  Velocity changes as a result of wavelength change.

 Also known as a mirage – false or distorted image  On a sunny day air is hotter closer to the surface of the road or hot sand – as light goes through the cooler air into the hotter air, the light waves bend and make it look like there are layers of water

 Polarized light waves vibrate only in one plane

 Scattering- light is redirected as it passes through a medium

 Small particles in the atmosphere scatter shorter wavelength blue light more than light of longer wavelengths – the only light that hasn’t been scattered by the time your eyes see it is the red and orange  When the sun is high in the sky its light travels a shorter distance through the earth’s atmosphere and scatters