# Electromagnetic Waves the Electromagnetic Spectrum Electromagnetic Waves Transverse

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Electromagnetic Waves & the Electromagnetic Spectrum

Electromagnetic Waves • Transverse waves without a medium! • (They can travel through empty space)

• They travel as vibrations in electrical and magnetic fields. – Have some magnetic and some electrical properties to them.

TRAVEL AT THE SPEED OF LIGHT– around 300, 000 m/s –the speed of light! (sound is 342 m/s) At this speed they can go around the world 8 times in one second.

Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency RADIO WAVES INFRARED RAYS MICROWAVES ULTRAVIOLET RAYS VISIBLE LIGHT GAMMA RAYS X-RAYS

Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)

1. RADIO WAVES & Microwaves Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.

Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from several satellites to the receiver, determining the distance to each satellite.

MRI (MAGNETIC RESONACE IMAGING) Uses Short wave radio waves with a magnet to create an image.

Radio Waves: Radio (music) and Radar Guns RADAR (Radio Detection and Ranging) • Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

MICROWAVES They are the shortest radio waves. Used in microwave ovens – to cook food!

2. INFRARED RAYS Infrared= below red Shorter wavelength and higher frequency than microwaves. Below our range of vision

INFRARED RAYS Infrared rays are used in remote controls and other sensors

Reading the Heat loss of homes You can feel the longest ones as warmth on your skin Warm objects give off more heat energy than cool objects.

3. VISIBLE LIGHT Electromagnetic waves we can see. Longest wavelength= red light Shortest wavelength= violet (purple) light

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

4. ULTRAVIOLET RAYS Shorter wavelength and higher frequency than visible light Carry more energy than visible light

Used to kill bacteria. (Sterilization of equipment)

Ultravioet Rays can damage skin! Too much can cause skin cancer. Use sun block to protect against (UV rays)

5. X- RAYS Shorter wavelength and higher frequency than UVrays Carry a great amount of energy Can penetrate most matter.

Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the xray was absorbed)

Why the Lead Vest? Ever have to wear a lead vest at the dentist or the doctor? ? ? X Rays so strong, they can cause cancer

6. GAMMA RAYS Shorter wavelength and higher frequency than X-rays Carry the greatest amount of energy and penetrate the most.

Used in radiation treatment to kill cancer cells. Can be very harmful if not used correctly.

The Incredible Hulk was the victim of gamma radiation.

Exploding nuclear weapons emit gamma rays.

Brief SUMMARY A. All electromagnetic waves travel at the same speed. (300, 000 meters/second) in a vacuum. B. They all have different wavelengths and different frequencies. – Long wavelength- lowest frequency – Short wavelength highest frequency – The higher the frequency the higher the energy.

TAKE OUT INTRO TO WAVES HANDOUTS FROM MONDAY

When Waves Hit Things Reflection: The wave bounces off the new medium and can change direction

When Waves Hit Things Reflection: The wave bounces off the new medium and can change direction EXAMPLES? ECHO MIRROR COLORS WE SEE

Refraction: The wave enters a new medium and changes speed This is responsible for “weirdness” when you look at things through water – magnification, warping, etc…

Refraction: The wave enters a new medium and changes speed EXAMPLES? Looking in a fish tank Your voice sounds different to yourself than when you hear it on a recording

Diffraction: The wave bends around corners or edges of a barrier

Diffraction: The wave bends around corners or edges of a barrier EXAMPLES? You see light from other room You can hear someone from around a corner

TAKE 5 Minutes: Label the parts and match the definitions of a Transverse wave and a Longitudinal (Compressional) Wave

Frequency of a wave Frequency: the number of waves that pass a point in a given amount of time. Measured in Hertz (Hz)

TEST THE RELATIONSHIP BETWEEN WAVELENGTH AND FREQUENCY USING SLINKYS

Go get your clicker!

What is the relationship between wavelength and frequency of waves? Frequency Up Wavelength?

Speed of Waves Wave speed is equal to the frequency of the wave times the wavelength. Vw = f λ (units: meters/second, or equivalent) Look at that formula – if Vw stays the same. What can you say about f and λ?

Practice 1) A wave has frequency of 50 Hz and a wavelength of 10 m. What is the speed of the wave? 11/1/2020

Practice 2) A wave has frequency of 5 Hz and a speed of 25 m/s. What is the wavelength of the wave? 11/1/2020

3) A flute is played and hits a note with a soundwave that is 512 Hz in frequency. The speed of the sound in the air is 342 m/s What is the length of the wave? 11/1/2020

CONSTRUCTIVE AND DESTRUCTIVE INTERFERENCE CONSTRUCTIVE: WAVES in sync make a bigger amplitude – RESONANCE remember this? resonance 1 Check this out: Rubens Tube

CONSTRUCTIVE AND DESTRUCTIVE INTERFERENCE DESTRUCTIVE: WAVES with same frequency and wavelength cancel each other out if not in sync

SOUND!

Sound – as Waves LONGITUDINAL (COMPRESSIONAL) WAVES SOUND WAVES MUST HAVE a MEDIUM TO TRAVEL THROUGH. Travel fastest in a solid. WHY AGAIN?

Sound – as Waves Amplitude = volume Frequency = pitch. High frequency, high pitch. Low frequency, low pitch. Lets try SOUND SIMULATOR

Measuring Sound Decibel – a measure of the Sound Pressure Level. The higher the decibel, the more intense the sound.

Whisper Quiet Library at 6' 30 d. B Normal conversation at 3' 60 -65 d. B City Traffic (inside car) 85 d. B Level at which sustained exposure may result in hearing loss 90 - 95 d. B Power mower at 3' 107 d. B Listening to music with headphones 105 -120 d. B (earbuds add 69 d. B) Pain begins 125 d. B 12 Gauge Shotgun Blast 165 d. B Death of hearing tissue 180 d. B Loudest sound possible 194 d. B

WHAT DID YOU SAY? people using that standard earbud could listen at about 80% of maximum volume for 90 minutes per day or less without increasing their risk for noise-induced hearing loss. But the louder the volume, the shorter your duration should be. At maximum volume, you should listen for only about 5 minutes a day.

Why am I telling you this? PROTECT YOUR HEARING!! Don’t go deaf!

August 27, 1883 Krakatoa 180 d. B Loudest sound ever heard. The sound itself caused tsunamis

The Doppler Effect The what? The Doppler Effect Explained The “perceived” change in frequency of an object’s sound when the source and the observer are in motion relative to each other. Draw an example:

Cool sound stuff… Supersonic (faster than the speed of sound) Subsonic (slower than the speed of sound) Sonic boom (what happens when you pass the speed of sound) Infrasound (below 20 Hz)

Yay, Tuning Forks! Look at the tuning forks I have given you. Locate someone near you with a different sized tuning fork. Compare the sounds of your two forks. Which one is lower? Now look at the forks and compare the numbers…what do you think the number stands for?

Before you go! Take out a small piece of paper, put your name on it. Use the speed of sound 342 m/s and the frequency of your tuning fork to find the wavelength of the sound wave your tuning fork makes. (share fork with neighbor if they don’t have one)