Science 8 Final Study Guide: Waves and Evolution

Wavelength ($\lambda$)

The distance between two consecutive identical points on a wave, such as from crest to crest or trough to trough. Unit: Typically measured in meters (m).

Amplitude

The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. Significance: Related to the energy carried by the wave (larger amplitude = more energy). For sound, it relates to loudness; for light, it relates to brightness.

Crest

The highest point or peak of a wave.

Trough

The lowest point or valley of a wave.

Frequency ($f$)

The number of complete wave cycles (or oscillations) that pass a given point in a certain amount of time. Unit: Hertz (Hz), which means cycles per second.

Pitch

How high or low a sound is perceived. Relationship to Waves: For sound waves, pitch is directly determined by the wave's frequency. High frequency = high pitch; low frequency = low pitch.

Wave Equation

The universal wave equation relates wave speed, wavelength, and frequency: v = \lambda f Where: $v$ = wave speed (velocity), typically in meters per second (m/s), $\lambda$ = wavelength, in meters (m), $f$ = frequency, in Hertz (Hz).

Finding speed example

A wave has a wavelength of 2 meters and a frequency of 5 Hz. What is its speed? $v = (2 \text{ m}) \times (5 \text{ Hz}) = 10 \text{ m/s}$.

Finding wavelength example

A wave travels at 30 m/s and has a frequency of 10 Hz. What is its wavelength? $\lambda = v / f = (30 \text{ m/s}) / (10 \text{ Hz}) = 3 \text{ m}$.

Finding frequency example

A wave travels at 50 m/s and has a wavelength of 5 meters. What is its frequency? $f = v / \lambda = (50 \text{ m/s}) / (5 \text{ m}) = 10 \text{ Hz}$.

Mechanical Waves

Waves that require a medium (matter) to travel through. They cannot travel through a vacuum. Examples: Sound waves, water waves, seismic waves (earthquakes), waves on a string.

Electromagnetic (EM) Waves

Waves that do not require a medium to travel. They can travel through a vacuum (like space) as well as through matter. They consist of oscillating electric and magnetic fields. Examples: Light, radio waves, microwaves, X-rays, gamma rays (all part of the EM spectrum).

Transverse Waves

Waves in which the particles of the medium oscillate perpendicular (at right angles) to the direction the wave is traveling. Characteristics: Have distinct crests and troughs. Examples: All electromagnetic waves (light), waves on a string, some water waves.

Longitudinal Waves

Waves in which the particles of the medium oscillate parallel to the direction the wave is traveling. Characteristics: Have compressions (regions where particles are close together) and rarefactions (regions where particles are spread apart). Examples: Sound waves, waves in a Slinky spring (when pushed and pulled).

Mechanical vs. EM Waves

Mechanical need a medium; EM don't.

Transverse vs. Longitudinal Waves

Transverse waves have oscillations perpendicular to wave direction; longitudinal waves have oscillations parallel to wave direction.

Medium

The substance through which a wave travels.

Solid Medium

Examples include rock, metal, and wood.

Liquid Medium

Examples include water and oil.

Gas Medium

An example is air.

Vacuum

The emptiness of space with no particles.

Speed of Mechanical Waves

Depends on the properties of the medium; sound travels fastest in solids, slower in liquids, and slowest in gases.

Energy and Amplitude

The amplitude of a wave is directly related to the amount of energy it carries; larger amplitude means more energy.

Sound Waves and Amplitude

A larger amplitude means a louder sound.

Light Waves and Amplitude

A larger amplitude means brighter light.

Frequency and Energy

The frequency of a wave is directly related to its energy, particularly for electromagnetic waves (E = hf).

Absorption

When a wave's energy is taken up by the medium, converting it into other forms of energy.

Diffusion

The spreading out of light or sound waves in many directions after encountering a rough surface or uneven medium.

Diffraction

The bending or spreading of waves as they pass through an opening or around an obstacle.

Transmission

When a wave passes through a medium without being absorbed or reflected.

Reflection

The bouncing back of a wave when it encounters a boundary or surface that it cannot pass through.

Refraction

The bending of a wave as it passes from one medium to another with a different wave speed.

Electromagnetic Spectrum

The entire range of all types of electromagnetic radiation, ordered by wavelength and frequency.

Components of Electromagnetic Spectrum

Includes Radio Waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, and Gamma Rays, ordered from longest wavelength/lowest frequency to shortest wavelength/highest frequency.

Radio Waves

Have the longest wavelengths and lowest frequencies.

Microwaves

Have long wavelengths and low frequencies.

Infrared Waves

Have long wavelengths.

Long wavelengths

Radio waves, Microwaves, Infrared.

Short wavelengths

Ultraviolet, X-rays, Gamma rays.

Inverse Relationship

Wavelength and frequency are inversely proportional ($v = au f$, and $v$ is constant for EM waves in a vacuum, which is the speed of light $c \approx 3 \times 10^8 \text{ m/s}$).

Wavelengths (Visible Light Spectrum)

The visible light portion of the EM spectrum is very narrow. Different colors correspond to different wavelengths within this range.

Spectrum

The colors of the visible light spectrum, in order from longest wavelength to shortest wavelength (and lowest frequency to highest frequency), are ROYGBIV: Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Rainbows

Formed when sunlight (white light) is refracted and reflected by water droplets in the atmosphere.

White objects

Reflect all wavelengths of visible light.

Black objects

Absorb all wavelengths of visible light.

Absorption & Reflection

The color of an object that you perceive is the color of light that the object reflects.

How do we see rainbows

Sunlight hits water droplets, refracts, reflects internally, and refracts again, separating into the visible spectrum.

How do we see objects

We see objects because they either emit light or reflect light.

Fossil Record

The sequence of fossils found in layers of sedimentary rock that shows the history of life on Earth.

Natural Selection

The process by which organisms that are better adapted to their environment tend to survive and produce more offspring.

Variation

Individuals within a species show variation in their traits.

Overproduction

Organisms produce more offspring than can survive.

Competition

There is competition for limited resources (food, shelter, mates).

Survival of the Fittest

Individuals with traits best suited to their environment are more likely to survive, reproduce, and pass those favorable traits to their offspring.

Adaptation

Over generations, these advantageous traits become more common in the population.

Human Impact Connection

Human activities can significantly influence the processes of natural selection and lead to rapid changes in species.