8th Grade Science Study Guide: Waves & Properties of Light

I. Key Concepts

1. Waves and Their Properties

• Wave: A disturbance that transfers energy from one place to another.

• Types of Waves:

  • Transverse Wave: Particles move perpendicular to the wave direction (e.g., light waves).

  • Longitudinal Wave: Particles move parallel to the wave direction (e.g., sound waves).

• Parts of a Wave:

  • Crest: Highest point of a transverse wave.

  • Trough: Lowest point of a transverse wave.

  • Wavelength (λ): Distance between two consecutive crests or troughs.

  • Frequency (f): Number of waves passing a point per second (measured in Hertz, Hz).

  • Amplitude: Height of the wave, related to energy.

Sound - 

Does NOT need a medium to pass through

Behaves like a wave AND a particle

A particle of light is called a photon

• Photons have no mass and behave in a “dual nature”

Light - 

Vibrations that travel through a medium (MATTER)

2. Sound vs. Light

3. Properties of Light

• Reflection: Light bouncing off a surface (e.g., mirrors).

• Refraction: Light bending when passing through a new medium (e.g., lenses).

• Diffraction: Light spreading out as it passes through a small opening.

• Absorption: Light energy taken in by an object (e.g., dark colors absorbing more heat).

4. Electromagnetic Spectrum

• Visible Light: Just a small part of the electromagnetic spectrum.

• Order from longest to shortest wavelength:

  • Radio Waves → Microwaves → Infrared → Visible Light → Ultraviolet → X-rays → Gamma Rays

• Visible Light Spectrum Colors:

  • Red = Longest wavelength, lowest frequency

  • Violet = Shortest wavelength, highest frequency

5. Dual Nature of Light

• Particle Nature: Light consists of photons (tiny particles of energy).

• Wave Nature: Light behaves like a wave (explains diffraction and interference).

• Evidence:

  • Young’s Double-Slit Experiment showed that light creates an interference pattern, proving its wave nature.

  • Photoelectric Effect (Einstein) showed that light can eject electrons from metals, proving its particle nature.

6. Emission of Light and the Bohr Model [DRAW MODEL]

• Ground State: Electron at its lowest energy level.

• Excited State: Electron absorbs energy and moves to a higher level.

• Photon Release: When an electron falls back down, it releases a photon (light energy).

• Different elements emit different colors of light based on their energy levels.

II. Important Formulas

1. Wave Speed Formula:
   

2. Frequency-Formula

   • Number of wavelengths/time=frequency

     • Measured in hertz

3. Frequency-Wavelength Relationship:
   
   

   • Inverse relationship:

     • If frequency increases, wavelength decreases.

     • If frequency decreases, wavelength increases.

4. Speed of Light:

   • Measured in meters per second, needs to be converted from cm (o.o_)

EXTRA CREDIT****

What properties of light are used in how we see light?

1. Reflection & Refraction – Light bends as it passes through the cornea and lens to focus on the retina.

2. Absorption – Different wavelengths of light are absorbed by rod and cone cells in the retina.

3. Transmission – Light travels through the eye until it reaches the retina, where it is processed into signals.

4. Color Perception – Cone cells detect different wavelengths corresponding to colors (red, green, and blue).

How are these used in how vision abnormalities are corrected?

• Refraction is corrected with glasses or contact lenses, which bend light properly onto the retina for nearsightedness (myopia) or farsightedness (hyperopia).

• Laser eye surgery (LASIK) reshapes the cornea to correct how light is refracted.

• Color blindness is linked to cone cell deficiencies, and specialized lenses can help enhance color perception.