Sound, Light, Mirrors, Lenses and Color Chapter 12

Sound The speed of sound depends on the medium which it travels through. The speed of sound depends on the medium which it travels through. In air, the speed of sound is 340 m/s In air, the speed of sound is 340 m/s Sound waves travel faster through liquids and solids than gases Sound waves travel faster through liquids and solids than gases

Sound… Intensity: describes the loudness of a sound from the source Intensity: describes the loudness of a sound from the source The loudness depends on the energy the wave carries-this is called amplitude The loudness depends on the energy the wave carries-this is called amplitude Pitch is used to describe how high or low a note sounds. Pitch is used to describe how high or low a note sounds. For example: Small instruments produced high pitched sounds because they have high frequencies, large instruments produce low pitched sounds because they have low frequencies For example: Small instruments produced high pitched sounds because they have high frequencies, large instruments produce low pitched sounds because they have low frequencies

Sound… Humans hear sound in a limited frequency Humans hear sound in a limited frequency Frequency of 20 Hz – Hz Frequency of 20 Hz – Hz Dogs can hear up to Hz Dogs can hear up to Hz Dolphins can hear up to Hz! Dolphins can hear up to Hz! We measure the volume of sound with the unit decibel We measure the volume of sound with the unit decibel

Decibel Scale

Ears and Hearing Ears sense vibrations, amplifies them, and transmits them as signals to the brain Ears sense vibrations, amplifies them, and transmits them as signals to the brain Sound waves enter the ear, strike the eardrum, travel through the three bones in the middle ear, enter the basilar membrane, travel through the cochlea, stimulate hair cells, which in turn sends nerve impulses to the brain. Sound waves enter the ear, strike the eardrum, travel through the three bones in the middle ear, enter the basilar membrane, travel through the cochlea, stimulate hair cells, which in turn sends nerve impulses to the brain.

The Human Ear

Waves and Particles There are two models that try to describe what light exactly is There are two models that try to describe what light exactly is One model describes light as a wave One model describes light as a wave The other model describes light as a particle The other model describes light as a particle

Light Light produces patterns like water waves. Light produces patterns like water waves.

Light… Light can also act like a particle Light can also act like a particle Dim Blue light strikes a piece of metal and electrons fly off the metal’s surface. Dim Blue light strikes a piece of metal and electrons fly off the metal’s surface. Bright Red light SHOULD have more energy than blue light because it has a greater amplitude (it’s brighter) and more electrons should fly off. Bright Red light SHOULD have more energy than blue light because it has a greater amplitude (it’s brighter) and more electrons should fly off. But… that’s not the case But… that’s not the case Conclusion: Light travels as photons, too Conclusion: Light travels as photons, too

A Wave or a Particle? Which model is correct? Which model is correct? Most scientists accept both theories as correct and use one or the other depending on what they are studying Most scientists accept both theories as correct and use one or the other depending on what they are studying Both models accurately describe how light behaves in separate situations Both models accurately describe how light behaves in separate situations

Reflection Light is modeled as a ray that reflects in many directions Light is modeled as a ray that reflects in many directions Smooth surfaces reflect light in one direction Smooth surfaces reflect light in one direction Rough surfaces reflect light in many directions Rough surfaces reflect light in many directions

Reflection This brings us to the Law of Reflection This brings us to the Law of Reflection “The angle of incidence= the angle of reflection”

Mirrors Demonstrate Reflection Example: You perceive yourself to be behind the mirror as you look inside it Example: You perceive yourself to be behind the mirror as you look inside it The virtual image appears to be as far behind the mirror as you are in front of it The virtual image appears to be as far behind the mirror as you are in front of it

Mirrors Virtual Image – image that light rays do not actually come from – its not where it appears to be. Virtual Image – image that light rays do not actually come from – its not where it appears to be.

Mirrors Real Image – Image formed by light rays coming together in the same spot Real Image – Image formed by light rays coming together in the same spot

Mirrors Convex Mirror – bent “outward” Convex Mirror – bent “outward” Concave Mirror – bent “inward” Concave Mirror – bent “inward”

Refraction vs. Reflection Some objects REFLECT light- turn it around and send it back (mirrors) Some objects REFLECT light- turn it around and send it back (mirrors) Other objects REFRACT light- bending light and changing it’s angle Other objects REFRACT light- bending light and changing it’s angle

Dispersion and Prisms Dispersion: the effect to which white light separates into it’s colors Dispersion: the effect to which white light separates into it’s colors Prisms: the objects that cause dispersion Prisms: the objects that cause dispersion

Dispersion Rainbows are caused by dispersion Rainbows are caused by dispersion The Rain Drops act as prisms The Rain Drops act as prisms

Lenses Work through refraction – waves bend when passing through glass Work through refraction – waves bend when passing through glass Concave (diverging) Convex (converging) Concave (diverging) Convex (converging)

Human Eye Eyes use lenses to focus an image (real) onto the retina on the back of the eye Eyes use lenses to focus an image (real) onto the retina on the back of the eye

Objects have color because they reflect certain wavelengths of white light Objects have color because they reflect certain wavelengths of white light

If you change the color of light, you change the light waves being reflected If you change the color of light, you change the light waves being reflected Blue Box Now Looks Black All Red Light Waves No blue light is available to reflect the color of the blue box

Light color may be added or subtracted to produce different colors Light color may be added or subtracted to produce different colors Televisions and computers combine the primary LIGHT colors- red, green and blue Televisions and computers combine the primary LIGHT colors- red, green and blue Subtraction Addition

Mixing primary colors together (red, blue and green) = Secondary colors (yellow, cyan, and magenta) AND White light Mixing primary colors together (red, blue and green) = Secondary colors (yellow, cyan, and magenta) AND White light That’s color addition That’s color addition

Mixing secondary colors (yellow, cyan and magenta) = primary colors (red, blue and green) AND, the ABSENCE of color (Black) Mixing secondary colors (yellow, cyan and magenta) = primary colors (red, blue and green) AND, the ABSENCE of color (Black) That’s color subtraction That’s color subtraction

The End!!