<aside>

• Incident ray – the incoming light ray that strikes a surface.
• Reflected ray – the light ray that bounces off the surface.
• Refracted ray – ray that bends inside the new medium.
• Normal – imaginary line drawn perpendicular (90°) to the surface at the point of incidence.
• Angle of incidence (θ₁) – angle between the incident ray and the normal.
• Angle of reflection (θ₂) – angle between the reflected ray and the normal. </aside>

wave basics

• A wave is a disturbance that transfers energy from one place to another without transferring matter.
• An oscillation is a repetitive back-and-forth or up-and-down motion about an equilibrium position (e.g., a plucked string or a pendulum).
• Mechanical waves require a medium (solid, liquid, gas) to travel (e.g., sound, water waves).
• Electromagnetic waves do not require a medium and can travel through vacuum (e.g., light, radio).
• Speed of light = 3x10$^8$

Wave characteristics:

• Amplitude (A): Maximum displacement from the rest position. Higher amplitude = more energy.
• Wavelength (λ): Distance between two consecutive crests, troughs, or compressions.
• Frequency (f): Number of complete waves passing a point per second (Hz).
• Period (T): Time taken for one wave to pass a point.
• Wave speed (v): The speed at which a wave travels.

Types of waves:

• Transverse: Particle oscillations are perpendicular to the direction of wave travel.
  • Examples: water waves, electromagnetic waves (light, radio).

• Longitudinal waves: Particle oscillations are parallel to the direction of wave travel. They have compressions (particles close together) and rarefactions (particles spread apart).
  • Examples: sound waves, compressions in a slinky.

• Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave
• The image below illustrates how wavefronts are visualised:
  • The arrow shows the direction the wave is moving and is sometimes called a ray
  • The space between each wavefront represents the wavelength
  • When the wavefronts are close together, this represents a wave with a short wavelength
  • When the wavefronts are far apart, this represents a wave with a long wavelength

Wave speed:

• The distance travelled by a wave each second
• Wave speed is given the symbol ****ν and is measured in metres per second (m/s)
• Wave speed is the speed at which energy is transferred through a medium
• Transverse and longitudinal waves both obey the wave equation:
  • v = f × λ

Where:

• v = wave speed in metres per second (m/s)
• f = frequency in hertz (Hz)
• λ = wavelength in metres (m)

Units:

f → Hz

T → s

λ → m

v → m/s.