Sound and Light

Chapter 12

Sound

A longitudinal wave that spreads in all directions

Speed depends on medium– Solids and liquids = quick movement– Gasses = slower movement– Increase temperature = increase speed

Intensity

Loudness of the sound– Increase amplitude = increase energy =

increase loudness = increase intensity– Increase distance = decrease intensity

Measured in decibels (dB)

Intensity

Pitch

Perceived loudness of a sound

Depends on frequency– Increase frequency = increase pitch

Infrasound vs. Ultrasound

Infrasound– Frequency below 20 Hz– Hard for human to hear (too low)

Ultrasound– Frequency above 20,000 Hz– Hard for human to hear (too high)

Uses of Sound

Sonar– Sound Navigation and Ranging– Reflect sound waves to show distance

Sonogram– Echoes (reflections) of very high frequency

sound waves – Can see inside animals

Are these infrasound or ultrasound?

Uses of Sound

Musical Instruments– Produce sound by vibrating air, solids, and

strings– Resonance helps produce the sound

• One vibrating object causes another object to vibrate

Light

Can be explained as waves– Electromagnetic waves– Spread in all directions– Used to explain most of the light we see

Can be explained as particles– A stream of tiny particles (photons) moving

very quickly

Speed of Light

Fastest in a vaccum– 3 x 108 m/s (186,000 mi/s)

Other speeds depend on the medium– Slows down in all cases– Gas is the fastest, then water, then

transparent solids

Intensity of Light

Brightness of light– Increase energy = increase brightness =

increase intensity– Increase distance = decrease intensity

Reflection of Light

Smooth surfaces reflection light in one direction

Flat surface

In-coming wave Incident wave

Out-going wave Reflected wave

Law of Reflection

Angle of incidence is equal to the angle of reflection

Flat surface

Incident angle

Reflected angle

Reflections of Light

Rough surfaces reflect light in many directions

Roughsurface

Reflection of Light

Mirrors can cause reflections to change– Flat mirrors create virtual images

• Image that appears to be behind or far away from where you are looking

– Curved mirrors create distortions (changes)

• Convex = bulge out = stretch image• Concave = curve in = compress image

Reflections

ConcaveConvex

Electromagnetic Spectrum

Light at all possible energies, frequencies, and wavelengths

Electromagnetic Spectrum

Bending of Light

Light will bend as it passes from one medium to another– Known as refraction

Happens in the air to create a mirage– A virtual image that happens mostly as the

atmosphere heats up

Bending of LightLight is made of all colors so it appears white

Can be bent through a prism to separate white light into all colors – Known as dispersion

Color of Objects

Objects have color because of what is reflected

All light hits an object– White light hits– Some colors absorbed– Some colors reflected -

this the color you see