Waves, Light, & Sound

Can we see in the dark? You are in a DARK room. It is night time and we are currently in a NEW MOON phase. You are in a DARK room. It is night time and we are currently in a NEW MOON phase. How long will it take you to see your hand? How long will it take you to see your hand? –Discuss in small groups.

Can we see in the dark? We CANNOT see in the dark. You will NEVER see your hand. We CANNOT see in the dark. You will NEVER see your hand. If the above statement is true, then why can you ‘see’ things after being in a dark room for awhile? If the above statement is true, then why can you ‘see’ things after being in a dark room for awhile? –Like when you cannot fall asleep at night and objects in your room become visible

Can we see in the dark? Can we see in the dark? Light is reflected off your hand, that is why you can see it! Light is reflected off your hand, that is why you can see it! Where is the light coming from? Where is the light coming from? –The moon through your window –Blinking lights on laptops, alarm clocks, TV set-top boxes, etc… –It will take awhile for this light to reflect off other objects and reach your eye, which is why it takes time for you to see it! –DARKNESS is the absence of light (just like COLD is the absence of heat!)

What is a Wave? Wave – Represents energy traveling from one place to another Wave – Represents energy traveling from one place to another –Types: Sound Waves Sound Waves Light Waves Light Waves Radio Waves Radio Waves Microwaves Microwaves And more! But we’ll get there… And more! But we’ll get there…

Waves Some waves need a “medium” to travel through Some waves need a “medium” to travel through –Sound Waves (Mechanical Waves) –Medium: matter that moves the energy from one place to another Some waves can travel through empty space as well Some waves can travel through empty space as well –Light Waves (electromagnetic waves) –Remember Save The Penguins?

Parts of a wave Crest = Top of the wave Crest = Top of the wave Trough = Bottom of the wave Trough = Bottom of the wave Wavelength = The length of a complete wave from crest-to-crest or trough-to-trough Wavelength = The length of a complete wave from crest-to-crest or trough-to-trough Amplitude = Height of the wave from equilibrium Amplitude = Height of the wave from equilibrium

Parts of a Wave Draw it and label it! Use colored pencils! Draw it and label it! Use colored pencils! Label: Wavelength, crests, troughs, equilibrium position, amplitude Label: Wavelength, crests, troughs, equilibrium position, amplitude

What does it all mean? Wavelength – The smaller the wavelength, the higher the energy on the wave Wavelength – The smaller the wavelength, the higher the energy on the wave Frequency = The number of waves that can pass by in one second Frequency = The number of waves that can pass by in one second As wavelength decreases, frequency increases – why? As wavelength decreases, frequency increases – why?

Which has a higher amplitude? The higher the amplitude, the louder the noise level of a sound wave! The higher the amplitude, the louder the noise level of a sound wave!

Which has a longer wavelength? Longer wavelength = less energy Longer wavelength = less energy Sound waves: longer wavelength = lower pitch Sound waves: longer wavelength = lower pitch

Which has a higher frequency? Higher frequency = more energy Higher frequency = more energy Sound waves: higher frequency = higher pitch Sound waves: higher frequency = higher pitch

Waves and Mediums Medium: moves energy from one place to another Medium: moves energy from one place to another –any form of matter! Solid (rope), liquid (water), gas (air) When a wave hits a medium, it can be… When a wave hits a medium, it can be… –Reflected –Absorbed –Transmitted –What do you think these terms mean?

Reflection Energy hits a substance and bounces back! Energy hits a substance and bounces back! Ex: Light waves bouncing off a mirror Ex: Light waves bouncing off a mirror Ex: Sound waves bouncing off a wall Ex: Sound waves bouncing off a wall –What do we call that?

Absorption Energy is ‘trapped’ by the medium Energy is ‘trapped’ by the medium –All the light or sound gets absorbed! Ex: Light waves get absorbed by a black surface (turn into HEAT) Ex: Light waves get absorbed by a black surface (turn into HEAT) Ex: Sound waves get absorbed by a ‘sound proof’ door Ex: Sound waves get absorbed by a ‘sound proof’ door

Reflection vs. Absorption Reflection vs. Absorption

Reflection vs. Absorption White Light = ALL the colors (reflects all colors) White Light = ALL the colors (reflects all colors) Black = NO color (absorbs all colors) Black = NO color (absorbs all colors) Whatever light wave is REFLECTED, that is what we see Whatever light wave is REFLECTED, that is what we see All other light waves are being absorbed All other light waves are being absorbed

What absorbs sound waves better? Hardwood floor OR carpeted floor? Hardwood floor OR carpeted floor? –How do you know? –What materials make good absorbers? –What

Transmission Energy is sent through the medium from one place to another Energy is sent through the medium from one place to another –It is transmitted from one place to another Ex: Refraction – light waves bend as they travel through a substance Ex: Refraction – light waves bend as they travel through a substance Ex: Scattering – waves spread out in all directions (sunsets and the blue sky) Ex: Scattering – waves spread out in all directions (sunsets and the blue sky) Ex: Hearing another class during our class – sound waves are transmitted through the walls Ex: Hearing another class during our class – sound waves are transmitted through the walls

Transmission Examples: Scattering Blue Sky Red/Yellow Sunset

Reflection vs. Transmission

Speed Speed of light = 186,000 miles per second Speed of light = 186,000 miles per second –That’s 300,000,000 meters per second! Speed of sound = 330 meters per second Speed of sound = 330 meters per second All electromagnetic (light) waves travel at the speed of light All electromagnetic (light) waves travel at the speed of light

Fireworks problem During a fireworks show, a family sees the spray of sparkles from an exploding firework high in the sky and, a moment later, hears the pop. Why does the pop and spray not seem to occur at the same time? During a fireworks show, a family sees the spray of sparkles from an exploding firework high in the sky and, a moment later, hears the pop. Why does the pop and spray not seem to occur at the same time?

Electromagnetic Spectrum

What is the Electromagnetic Spectrum? A table that describes the type of energy on a light wave A table that describes the type of energy on a light wave –It all depends on wavelength All of them can travel through space All of them can travel through space All of them travel at the speed of light All of them travel at the speed of light

The Electromagnetic Spectrum We can only see a small part of the spectrum with our eyes We can only see a small part of the spectrum with our eyes

Visible LightVisible Light – How do we see it? Visible Light Violet – Indigo – Blue – Green – Yellow – Orange - Red Violet – Indigo – Blue – Green – Yellow – Orange - Red Shorter Wavelength Longer Wavelength

Rainbows Rainbows form when light is transmitted (refracts and scatters) through raindrops. Rainbows form when light is transmitted (refracts and scatters) through raindrops. Raindrops act as a prism, revealing all parts of the visible light spectrum. Raindrops act as a prism, revealing all parts of the visible light spectrum.

What are all the others? Radio Waves – Carries TV signals, cell phone signals, radio signals, etc. Radio Waves – Carries TV signals, cell phone signals, radio signals, etc. Microwaves – used to cook food (duh!) Microwaves – used to cook food (duh!) Infrared Waves – Heat coming off an object is in infrared Infrared Waves – Heat coming off an object is in infrared

More Electromagnetic Waves Ultra Violet – Harmful waves from the sun Ultra Violet – Harmful waves from the sun X-Rays – Used to take photographs of bone – How does it work? X-Rays – Used to take photographs of bone – How does it work?How does it work?How does it work?

One More… One More… Gamma Waves – Radiation released from nuclear explosions and radioactive elements Gamma Waves – Radiation released from nuclear explosions and radioactive elements –Used for treating cancer cancer