Warmup- Monday 16th

1.In which kind of wave does the matter move perpendicular to the movement of the energy?

a. longitudinal b. transverse

2. Which waves have troughs and crests?

a. Longitudinal b. transverse

3.What happens to the wavelength as you increase the frequency of the wave?

a. Gets Longer b. Gets Shorter

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 Practice Practice

26/03/2015

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

Practice Practice Practice

26/03/2015

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

26/03/2015

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/sWhat is the length of the wave?

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 300,000,000 m/s

–the speed of light! (sound is 342m/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

MICROWAVES

INFRARED

RAYS

VISIBLE LIGHT

ULTRAVIOLET

RAYS

X-RAYS

GAMMA

RAYS

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

1. RADIO WAVES & MICROWAVES

Have the longestwavelengths and

lowestfrequencies 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

skinWarm 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 lightCarry 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 UV-rays

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 x-

ray 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 energyand 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 SUMMARYA. All electromagnetic waves travel at the same

speed. (300,000,000 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 ThingsReflection:

The wave bounces off the new medium and can

change direction

When Waves Hit ThingsReflection:

The wave bounces off the new medium and can

change direction

EXAMPLES?

ECHO

MIRROR

COLORS WE SEE

Refraction

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

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

Diffraction: The wave bends around

corners or edges of a barrier

Diffraction

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)

timef

wavesof#

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?

CONSTRUCTIVE AND

DESTRUCTIVE

INTERFERENCE

CONSTRUCTIVE:

WAVES in sync make a bigger amplitude –

RESONANCE

remember this? resonance1

Check this out: Rubens Tube

CONSTRUCTIVE AND

DESTRUCTIVE

INTERFERENCE

DESTRUCTIVE:

WAVES with same frequency and wavelength

can cancel each other out if not in sync

SOUND!

Sound – as WavesLONGITUDINAL (COMPRESSIONAL)

WAVES

SOUND WAVES MUST HAVE a

MEDIUM TO TRAVEL THROUGH.

Travel fastest in a solid. WHY AGAIN?

Sound – as WavesAmplitude = 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' 30dB

Normal conversation at 3' 60-65dB

City Traffic (inside car) 85dB

Level at which sustained

exposure may result in

hearing loss

90 - 95dB

Power mower at 3' 107dB

Listening to music with

headphones

105-120 dB (earbuds add 6-

9 dB)

Pain begins 125dB

12 Gauge Shotgun Blast 165dB

Death of hearing tissue 180dB

Loudest sound possible 194dB

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 dB

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:

Period of a Wave

PERIOD – The period of TIME it takes for

1 wave to pass.

This is related to Frequency…..

T=1/f

What is the period of this

wave?

A wave with a frequency of 200Hz

T= 1/f

T=1/200

T=.005s

It takes .005s for 1 wave to pass

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)