ELECTROMAGNETIC WAVES AND THE EM SPECTRUM MR. BANKS 8 TH GRADE SCIENCE

Transcription

1 ELECTROMAGNETIC WAVES AND THE EM SPECTRUM MR. BANKS 8 TH GRADE SCIENCE

2 ELECTROMAGNETIC WAVES Do not need matter to transfer energy. Made by vibrating electric charges. When an electric charge vibrates, the electric field around it changes creating a magnetic field.

3 ELECTROMAGNETIC WAVES What type of wave is this?

4 EM WAVES All matter contains charged particles that are always moving; therefore, all objects emit EM waves. The wavelengths become shorter as the temperature of the material increases. EM waves carry radiant energy.

5 EM WAVE SPEED All EM waves travel 300,000 km/sec in space. (the speed of light!) EM waves usually travel slowest in solids and fastest in gases. Material Speed (km/s) Vacuum 300,000 Air <300,000 Water 226,000 Glass 200,000 Diamond 124,000

6 REVIEW: WAVELENGTH AND FREQUENCY What did we already learn? Wavelength = distance from one point in the wave to the same point in the next. Frequency = number of wavelengths that pass a given point in 1 s. As frequency increases, The wavelength becomes smaller.

7 REVIEW What did we learn determined energy of a wave? The Amplitude

8 THE PHOTOELECTRIC EFFECT In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected. Albert Einstein explained Hertz s discovery: EM waves can behave as a particle and not a wave, he named the particles photons.

9 WAVE INTERFERENCE

10 WAVE DIFFRACTION Double slit experiment looking for wave interference

11 LIGHT AS A WAVE Double slit experiment looking for wave interference The alternating bands of light and dark demonstrated the wave nature of light.

12 WAVE-PARTICLE DUALITY The theory that light sometimes behaves like a wave and sometimes behaves like a particle (photon)

13 THE EM SPECTRUM The whole range of EM wave frequencies is called the electromagnetic spectrum. Different parts interact with matter in different ways. The frequencies humans can see are called visible light, a small part of the whole spectrum.

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15 RADIO WAVES Radio waves are low frequency EM waves with wavelengths longer than 1mm. These waves must be turned into sound waves by a radio before you can hear them. Used for radio, TV, cell phones, and WiFi.

16 RADIO WAVES Most radio waves are not blocked by the atmosphere.

17 MICROWAVES Microwaves are radio waves with wavelengths less than 30 cm (high frequency radio waves). Cell phones and satellites use microwaves between 1 cm & 20 cm for communication. Microwave ovens, use very high frequency/low wavelength waves to transfer energy to water molecules in the food causing them to vibrate and heat up.

18 CELL PHONE MICROWAVES Wait, am I cooking my head when I m on the phone? Not really. 0.2 C temperature rise

19 RADAR - RADIO DETECTING AND RANGING Uses radio waves to find the position and speed of objects using wave reflection by bouncing radio waves off the object.

20 MRI MAGNETIC RESONANCE IMAGING Uses 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.

21 LONG RANGE COMMUNICATION Before satellites, the only way to communicate long ranges wirelessly was to use short wave radio. Radio signals sent into the atmosphere at the right wavelength would reflect back to earth at extremely long ranges. Still used today to send signals to remote places.

22 SHORTWAVE RADIO ON THE INTERNET

23 INFRARED WAVES EM waves with wavelengths between 1mm & 750 nm. Used daily in remote controls, to read CDs Every object gives off infrared waves. Hotter objects give off more than cooler ones.

24 THERMOGRAPHY Using the emission of infrared waves to measure the temperature of something.

25 THERMOGRAPHY Using the emission of infrared waves to measure the temperature of something.

26 THERMOGRAPHY Using the emission of infrared waves to measure the temperature of something.

27 VISIBLE LIGHT Range of EM waves humans can see From 750 to 400 nanometers in length. You see different wavelengths as colors. Violet has shortest wavelength Red has the longest wavelength Light looks white if all colors are present

28 When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into its various colors ROYGBIV.

29 FIBER OPTICS Uses pulses of light to send digital data over large distances. Information literally travels at the speed of light. Makes up the primary backbone of the modern internet.

30 ULTRAVIOLET LIGHT EM waves with wavelengths from about 400 nanometers to 10 nanometers. Have enough energy to enter skin cells Directly damages DNA Which can cause skin cancer

31 IONIZING RADIATION Causes harm to living things

32 THE OZONE LAYER km above earth Absorbs most of the Sun s harmful UV rays The ozone layer was decreasing due to CFCs in AC, refrigerators, & cleaning fluids, but it s recovering.

33 THE OZONE LAYER Protects us from other harmful EM waves Without the ozone layer, even more harmful EM waves would reach earth

34 X-RAYS Shorter wavelength than UV radiation Carries a large amount of energy Can pass through much more matter Large doses can cause harm deeper than the skin

35 X-RAYS Bones and teeth can absorb X-Rays

36 GAMMA RAYS EM waves with the shortest wavelength Carries the greatest amount of energy Can pass the farthest through things Extremely harmful to living things

37 GAMMA RAYS Can be used in radiation treatments to kill cancer cells. Must be very careful, or it could cause much more harm than good.

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