Study Guide: Waves, Light, and Sound Energy

Wave: A repeating pattern that transfers energy from one place to another. Both sound and light energy travel through their environments as waves.
Medium: A material that energy travels through.
- Sound waves require a physical medium (like air, water, or solids) to travel.
- Light waves are unique because they do not require a material; they can travel through empty space (a vacuum).
Transmission: The transfer of energy through or between materials.
- Sound energy can be transmitted through air or water.
- Light energy can be transmitted through transparent objects.
Interference: The interaction of two waves when they meet. Interference can cause the amplitudes of the two waves to either add together (constructive) or cancel each other out (destructive).

Amplitude: The height of a wave, measured from the middle or rest position to the crest.
- In sound waves, amplitude relates to the loudness of the sound.
- In light waves, amplitude relates to the brightness of the light.
Frequency: The number of waves that go by a specific point in one second.
- Frequency is measured in the unit of waves per second ( $\text{waves/s}$ ).
- There is an inverse relationship between frequency and wavelength: higher-frequency waves have shorter wavelengths.
Wavelength: The physical distance between two consecutive wave crests (or peaks).
- In the visible spectrum, red light has the longest wavelengths.
- In sound, a wave with a long wavelength is perceived as having a low pitch.
Waveform: A graphical representation of a wave. For a sound wave, a waveform shows variations in the density of particles over time or space.

Light: A type of energy that travels in electromagnetic waves. Light energy is what allows us to see images, such as a person on a video call.
Electromagnetic Spectrum: The full range of frequencies of electromagnetic waves. Visible light represents only a small portion of the entire electromagnetic spectrum.
Radiation: Energy given off by objects in the form of waves or particles. Both visible light and infrared are specific types of radiation.
Photon: A particle of light. This concept is a key component in the particle model of light.
Ray: A straight line used to model the path of light. In a ray diagram, straight lines or arrows are utilized to model exactly how light interacts with various objects.
Models of Light:
- Particle Model: A representation of the transfer of energy by particles. This model is useful for understanding how light behaves in specific physical situations.
- Wave Model: A representation of the transfer of energy by waves. This model is useful for understanding how light waves from two separate sources interact with one another.

Absorption: The transfer of energy into an object rather than reflecting or transmitting it.
- Example (Light): A green leaf absorbs all the colors found in white light except for green, which it reflects.
- Example (Sound): Certain soft or porous materials, such as carpet, are highly effective at absorbing sound energy.
Reflection: The change in direction of light as it bounces off a surface. Human vision depends on reflection; we see objects when the reflected light enters our eyes.
Refraction: The change in direction of light as it passes from one material into a new material. Light is refracted as it enters and exits a lens.
Filter: An object that only transmits specific types of light while blocking others. For example, a red filter only transmits red light and absorbs all the other colors present in white light.
Lens: A transparent object with a curved surface. In a camera, light passes through the lens before it reaches the sensor.

Sound: A type of energy that travels through matter as vibrations.
- Example: When a tuning fork is struck, sound waves travel outwards from the fork as vibrations of air particles.
Density: A measure of the number of particles in a given area.
- A sound wave is composed of alternating areas of higher density (compressions) and lower density (rarefactions).

Encoding: The process of turning information into another form for communication or storage. Sign language is an example of encoding, where letters, words, and numbers are turned into visible gestures.
Digital Information: Information represented by discrete, distinct differences or symbols.
- Examples: A digital image on a smartphone; Morse code.
Analogue Information: Information represented by continuous differences rather than discrete steps.
- Examples: A printed image from an instant camera; the human voice.

Unmagnetized: Refers to a material that is not behaving like a magnet. This occurs when the magnetic domains within a magnetic material are not lined up in the same direction.
Gene: A unit of genetic information. A gene is a specific section of a $\text{DNA}$ molecule that contains the instructions for building a specific protein.