Unit 3: Waves, Sound and Light

What is a wave?

A disturbance that transfers energy from one place to another.

Do waves transfer energy or matter over long distances?

Energy. Particles of a medium usually vibrate around their positions rather than traveling with the wave.

How are mechanical waves created?

Energy makes matter vibrate or move back and forth, passing the disturbance along.

What is a medium?

Matter through which a mechanical wave travels, such as air, water, or rock.

What is a mechanical wave?

A wave that requires a medium. Examples include sound and seismic waves.

What is an electromagnetic wave?

A wave of oscillating electric and magnetic fields that can travel through matter or a vacuum. Light is one example.

Which wave type needs a medium: mechanical or electromagnetic?

Mechanical waves need a medium; electromagnetic waves do not.

What waves do earthquakes produce?

Seismic waves, which are mechanical waves traveling through Earth. Earthquake motion creates these waves.

What is a transverse wave?

A wave with vibrations perpendicular to the direction energy travels.

What is a longitudinal wave?

A wave with vibrations parallel to the direction energy travels.

What is the main difference between transverse and longitudinal waves?

Transverse vibrations are across the travel direction; longitudinal vibrations are along it.

What is a crest?

The highest point of a transverse wave above its rest position.

What is a trough?

The lowest point of a transverse wave below its rest position.

What is amplitude?

The greatest displacement from rest. For a transverse wave, measure from the midline to a crest or trough, not crest to trough.

What is wavelength?

The distance between matching points on consecutive waves, such as crest to crest or compression to compression.

What is frequency?

The number of complete wave cycles passing a point each second.

What unit measures frequency?

Hertz (Hz); one hertz means one cycle per second.

What is a compression?

A crowded region of a longitudinal wave where particles are close together.

What is a rarefaction?

A spread-out region of a longitudinal wave where particles are farther apart.

How do you measure wavelength on a longitudinal wave diagram?

From the center of one compression to the next, or one rarefaction to the next.

How do you recognize a transverse wave drawing?

It usually shows an up-and-down curve with crests and troughs.

How do you recognize a longitudinal wave drawing?

It usually shows alternating crowded and spread-out regions, like a compressed spring.

What happens to wave energy when amplitude increases?

The wave carries more energy.

At a constant wave speed, how are wavelength and frequency related?

Higher frequency means shorter wavelength; lower frequency means longer wavelength.

What is reflection?

A wave bounces off a surface or boundary.

What is refraction?

A wave changes direction because its speed changes when it enters a different medium at an angle.

What is diffraction?

A wave spreads around an obstacle or after passing through an opening.

What is absorption?

Matter takes in wave energy, often converting it to thermal energy.

What causes an echo?

Sound reflects from a surface and returns to the listener.

A straw looks bent in water. Which wave interaction explains this?

Refraction: light changes speed and direction between water and air.

You hear sound around a doorway. Which wave interaction helps explain this?

Diffraction: sound spreads through an opening and around edges.

What two classifications describe light?

Electromagnetic and transverse.

Does light need a medium?

No. Light can travel through a vacuum, including space.

What type of energy does the Sun send to Earth?

Radiant or electromagnetic energy, including visible light.

Which part of the EM spectrum can humans see?

Visible light, a narrow range of electromagnetic wavelengths.

Name the EM spectrum from lowest to highest energy.

Radio -> microwave -> infrared -> visible -> ultraviolet -> X-ray -> gamma ray.

Which EM waves have the longest wavelengths and lowest frequencies?

Radio waves.

Which EM waves have the shortest wavelengths and highest frequencies?

Gamma rays.

What happens to energy as EM frequency increases?

Energy per photon increases.

How do we see the color of an opaque object?

The object reflects some wavelengths to our eyes and absorbs others. The reflected light helps determine its color.

Why does a red object look red under white light?

It reflects red wavelengths toward our eyes and absorbs many other wavelengths.

Why do white objects look white under white light?

They reflect most visible wavelengths.

Why do black objects look black under white light?

They absorb most visible light and reflect little to our eyes.

What is the cornea?

The clear curved front surface of the eye; it protects the eye and bends incoming light.

What is the pupil?

The opening through which light enters the eye.

What is the iris?

The colored ring of muscle that changes pupil size to control how much light enters.

What is the sclera?

The tough white outer layer that protects the eye and helps hold its shape.

What does the eye's lens do?

It changes shape to focus light on the retina.

What is the retina?

The light-sensitive tissue at the back of the eye that converts light into electrical signals.

What does the optic nerve do?

It carries signals from the retina to the brain.

What is the eye's blind spot?

The place where the optic nerve exits the retina; it has no light-detecting cells.

What is the path of light and information through the eye?

Cornea -> pupil -> lens -> retina -> optic nerve -> brain. The iris controls pupil size.

What do rods and cones do?

Rods help with dim-light vision; cones detect color and fine detail in brighter light.

What two classifications describe sound?

Mechanical and longitudinal, for ordinary sound traveling through air.

What causes sound?

Vibrating matter creates compressions and rarefactions in a medium.

Can sound travel through a vacuum?

No. Sound requires matter to carry its vibrations.

In general, where does sound travel fastest: solids, liquids, or gases?

Fastest in solids, then liquids, and slowest in gases; exact speed depends on the material.

Why does sound generally travel faster in solids than in gases?

Solids transmit vibrations efficiently because particles interact strongly and the material is stiff.

What is the outer ear's job?

The pinna collects sound, and the ear canal directs it toward the eardrum.

What does the eardrum do?

It vibrates when sound waves strike it.

Name the three tiny middle-ear bones in order.

Hammer (malleus), anvil (incus), stirrup (stapes).

What do the middle-ear bones do?

They transmit and amplify vibrations from the eardrum toward the inner ear.

What is the cochlea?

A fluid-filled inner-ear structure where sensory hair cells convert vibrations into nerve signals.

What does the auditory nerve do?

It carries hearing signals from the inner ear to the brain.

What are the steps of hearing?

Sound enters the ear canal -> eardrum vibrates -> middle-ear bones transmit/amplify vibrations -> cochlea converts them to signals -> auditory nerve carries signals -> brain interprets sound.

Which structures belong to the middle ear?

The hammer, anvil, and stirrup; the eardrum forms its outer boundary.

Which structure is in the inner ear and converts vibrations to signals?

The cochlea.

What is pitch?

How high or low a sound seems; it depends mainly on frequency.

What happens to pitch when frequency increases?

Pitch becomes higher.

What happens to pitch when frequency decreases?

Pitch becomes lower.

What is loudness related to?

Sound intensity and amplitude. A larger amplitude generally produces a louder sound.

What unit is used for sound level?

Decibels (dB). Frequency is measured in hertz (Hz), not decibels.

What happens when sound amplitude increases but frequency stays the same?

The sound becomes louder while its pitch stays the same.

What happens when sound frequency increases but amplitude stays the same?

Pitch rises; amplitude has not increased.

What is the Doppler effect?

A change in observed frequency caused by relative motion between a wave source and observer.

How does an approaching siren sound compared with a receding siren?

Approaching: higher frequency and pitch. Moving away: lower frequency and pitch.

Why do we see lightning before hearing thunder?

Light travels much faster than sound, so it reaches us first.

Does louder sound necessarily have higher pitch?

No. Loudness relates to amplitude/intensity; pitch relates mainly to frequency.

Does an object create color wavelengths that are absent from the light shining on it?

Not in ordinary reflection. Its appearance depends on the available light and which wavelengths it reflects.

How are light and sound alike?

Both carry energy, have wavelength and frequency, and can reflect, refract, diffract, and be absorbed.

How are light and sound different?

Light is electromagnetic and crosses a vacuum; sound is mechanical and needs a medium.