8th Grade Science Study Guide: Waves & Properties of Light I. Key Concepts

Wave

A disturbance that transfers energy from one place to another.

Transverse Wave

A wave in which particles move perpendicular to the wave direction.

Longitudinal Wave

A wave in which particles move parallel to the wave direction.

Crest

The highest point of a transverse wave.

Trough

The lowest point of a transverse wave.

Wavelength (λ)

The distance between two consecutive crests or troughs.

Frequency (f)

The number of waves passing a point per second, measured in Hertz (Hz).

Amplitude

The height of the wave, related to its energy.

Medium

The matter through which a wave travels.

Photon

A massless particle of light that carries energy.

Bohr model

A model of the atom that describes electron energy levels.

Ground state

The lowest energy level of an electron.

Excited State

A higher energy level of an electron after absorbing energy.

Photon Emission

The release of energy in the form of a photon when an electron falls back to a lower energy level.

Reflection

The bouncing off of light from a surface.

Refraction

The bending of light when it passes through different materials.

Diffraction

The spreading out of light after passing through a narrow opening.

Absorption

The process by which light is taken in by a material.

Electromagnetic wave

A wave that can travel through empty space, such as light.

Inverse relationship

A relationship where an increase in one variable leads to a decrease in another.

Visible light spectrum

The range of wavelengths of visible light, including colors from red to violet.

Myopia

Nearsightedness; light focuses before reaching the retina.

Hyperopia

Farsightedness; light focuses behind the retina.

LASIK Surgery

A procedure to reshape the cornea to correct vision abnormalities.

Energy absorption

The process by which electrons absorb energy and move to an excited state.

Color blindness

A condition where one or more cone types in the retina do not function properly.

Rods

Photoreceptors in the retina that detect light intensity and are responsible for black and white vision.

Cones

Photoreceptors in the retina that detect color.

Light speed in vacuum

The speed at which light travels, which is fastest through empty space.

Sound speed in solids

Sound moves faster in solids due to closely packed molecules.

Color perception

The way our eyes interpret different wavelengths of light to perceive colors.

Wave speed equation

An equation used to determine the speed of a wave based on frequency and wavelength.

Frequency-wavelength relationship

The inverse connection between frequency and wavelength; as one increases, the other decreases.

1. Explain the “dual nature” of light and the behavior of a photon.

Light exhibits dual nature, meaning it behaves as both a wave and a particle.

• Wave nature: Light exhibits properties like diffraction, refraction, and interference, which are typical of waves.

Particle nature: Light is made up of discrete packets of energy called photons, which can eject electrons from metals in the photoelectric effect (Einstein’s discovery).

2. Medium and Its Role in Light vs. Sound

A medium is the matter through which a wave travels.

• Light Waves: Do NOT need a medium (can travel through empty space).

• Sound Waves: NEED a medium (air, water, or solid) because they are longitudinal waves that rely on particle vibrations.The medium affects the speed and propagation of sound waves, while light waves can travel without a medium.

 By using prior knowledge of chemistry diagrams, explain the process of how photons are released.

Using the Bohr model of the atom:

1. Energy Absorption: An electron absorbs energy and moves from its ground state (lowest energy level) to an excited state (higher energy level).

2. Unstable Excited State: The electron cannot stay in the excited state indefinitely.

3. Photon Emission: The electron falls back to a lower energy level, releasing energy in the form of a photon.

4. Different Colors: The energy released determines the wavelength of light emitted. For example:

   • Red light has a longer wavelength, lower frequency, and lower energy.

Blue/violet light has a shorter wavelength, higher frequency, and higher energy.

10. Visible light spectrum relationship to wavelength, frequency, and energy.

• Red light: Longest wavelength, lowest frequency, lowest energy.

• Violet light: Shortest wavelength, highest frequency, highest energy.

Energy is directly proportional to frequency and inversely proportional to wavelength.

 Identify a type of wave on the full electromagnetic spectrum and its frequency and wavelength in relationship to all waves (rank them).