Physics Chapter on Waves

Progressive Waves

• Transfer energy
• Types of waves: transverse and longitudinal
• Transverse waves: particle oscillation is perpendicular to wave energy direction
• Longitudinal waves: particle oscillation is parallel to wave energy direction
• Amplitude: maximum displacement of a particle from its rest position; measured in metres (m)
• Wavelength: distance between two adjacent wavefronts; measured in metres (m)
• Frequency: number of complete oscillations per unit time; measured in Hertz (Hz)
• Period: time taken for one complete oscillation; measured in seconds (s)
• Wave speed: distance moved by a wave per unit time; measured in metres per second (m/s)
• Wave speed equation: v = fλ = λ/T

Stationary Waves

• Formed when two identical waves travelling in opposite directions interfere
• Do not transfer energy
• Nodes: points of zero displacement
• Antinodes: points of maximum displacement

Intensity

• Defined as the rate of energy transmitted (power) per unit area at right angles to the wave velocity
• Measured in Watts per square metre (W/m²)
• Intensity is proportional to the square of amplitude
• Intensity is inversely proportional to the square of distance from the source

Phase

• Phase difference: the difference in position of two points on a wave, measured in degrees or radians
• In phase: phase difference of 0° or 360°
• Exactly out of phase: phase difference of 180°

Doppler Effect

• Observed frequency is different from the source frequency when the source moves relative to the observer
• Moving towards: observed frequency is higher, pitch is higher, moves towards blue in the electromagnetic spectrum
• Moving away: observed frequency is lower, pitch is lower, moves towards red in the electromagnetic spectrum

Electromagnetic Spectrum

• A range of electromagnetic waves, with varying frequencies and wavelengths
• Includes: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays

Polarisation

• Only transverse waves can be plane polarised
• Electromagnetic waves can be plane polarised
• Plane polarised: oscillations are in a single direction, perpendicular to the direction of wave propagation
• Longitudinal waves cannot be polarised: because they vibrate along the direction of wave travel, so no matter the orientation of the slit, the waves will be able to get through
• Malus’s Law: relates the intensity of polarised light after passing through a polariser to the angle between the polarisation direction of the light and the transmission axis of the polariser.
• Intensity after passing through the polariser is proportional to the square of the cosine of the angle between the polarisation direction and the transmission axis.

Progressive waves

• Transfer energy
• Can be longitudinal or transverse

Transverse waves

• Particle oscillation perpendicular to wave energy direction

Longitudinal waves

• Particle oscillation parallel to wave energy direction

Wave properties

• Amplitude: Maximum displacement from equilibrium position, measured in meters (m).
• Wavelength (λ): Distance between two adjacent wavefronts, measured in meters (m).
• Frequency (f): Number of complete oscillations per unit time, measured in Hertz (Hz).
• Period (T): Time taken for one complete oscillation, measured in seconds (s).

Wave speed

• Distance moved by the wave in a given time
• Calculated using the equation: wave speed (v) = distance moved by wave / time taken
• Can also be calculated using: v = λ / T = fλ
• Unit: meters per second (m/s)

Types of waves

• Progressive waves: Transfer energy forward
• Stationary waves: form when two waves of the same frequency and amplitude interfere, resulting in fixed points of maximum and minimum displacement called nodes and antinodes.

Intensity

• Rate of energy transmitted (power) per unit area at right angles to the wave velocity
• Calculated using the equation: Intensity = Power / Area, unit: W/m2
• Intensity is proportional to the square of amplitude: intensity ∝ amplitude²
• Intensity is inversely proportional to the square of distance: intensity ∝ 1/distance²

Phase

• The position of a point on a wave at a given time relative to a reference point.
• Phase difference can be calculated using the change in time, period or change in length and wavelength.
• Phase difference is measured in degrees or radians.
• Two waves are in phase when their crests and troughs align.
• Two waves are exactly out of phase when their crests align with the troughs of the other wave.

Doppler Effect

• Change in observed frequency when the source of the wave and the observer are moving relative to each other.
• Observed frequency is higher than source frequency when the source is moving towards the observer
• Observed frequency is lower than the source frequency when the source is moving away from the observer

Electromagnetic spectrum

• Waves produced by the vibrations of electric and magnetic fields.
• Transverse waves.
• Examples of uses: 3D movies, sunglasses, cameras.

Polarisation

• Transverse waves can be plane polarized.
• Plane polarized waves oscillate in a single direction perpendicular to the direction of wave propagation.
• Longitudinal waves cannot be polarized because they oscillate along the direction of wave travel.

Malus's Law

• Describes the intensity of light passing through a polarizer.
• The intensity of the light after passing through the polarizer is proportional to the square of the cosine of the angle between the polarization direction of the light and the transmission axis of the polarizer.
• Equation: I = I0(cosθ)², where I0 is the initial intensity of the polarized light and θ is the angle between the polarization direction and the transmission axis.

Test your understanding of progressive and stationary waves in this physics quiz. Explore key concepts such as amplitude, wavelength, frequency, and wave speed, along with the characteristics of wave interference involved in stationary waves. Perfect for students studying waves in their physics curriculum.