[PHY] Chapter 12 - General Wave Properties

DARRELL ER (COPYRIGHTED) TOPIC 12: GENERAL WAVE PROPERTIES DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT LEARNING EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

GENERAL WAVE PROPERTIES TRANSVERSE WAVE LONGITUDINAL WAVE KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

GENERAL WAVE PROPERTIES GENERAL WAVE PROPERTIES Definition: A wave is a disturbance that transfers energy through vibrations from one place to another, without the transfer of particles/matter itself. Two key properties of waves: - Carries energy away from the wave source - Transfers energy without transferring matter UNDERSTAND THIS CONCEPT! Particles will oscillate about their equilibrium position and in the process transfer energy. However after the wave have passed, the particles themselves do not shift away from their equilibrium position. For example, transverse waves’ particles oscillate up and down when a wave is going through. After the wave have passed, that particle will return to its equilibrium position. Scenario: Imagine a busy e-commerce warehouse. When there is a shipment, the warehouse gets busy and workers move around up & down the warehouse. But eventually the shipment gets delivered elsewhere down the line. Once that happens, the workers in the warehouse settles back into their default state. The workers themselves do not move out of the warehouse. DARRELL ER (COPYRIGHTED) ©

WAVE MOTION BASICS WAVE MOTION A wave motion is a method of transferring energy from one point to another, without any physical transfer of material. The hand generates kinetic energy, hence it is the source. The kinetic energy is transferred in the form of a wave motion to the other end of the rope. Kinetic energy is transferred but the rope is unchanged. There are two types of waves: transverse waves & longitudinal waves. DARRELL ER (COPYRIGHTED) ©

KEY TERMINOLGIES Terminology Formula Definition Crest High points on a wave. Trough Low points on a wave. Phase When 2 particles are moving in the same direction from the same relative position, they are in phase. The distance between 2 points in phase is the wavelength , λ. Amplitude Magnitude of the maximum displacement from the rest position (height of crest or depth of trough). Wavelength λ Distance between 2 successive crests/troughs (or any 2 successive points “in phase”). Period T = 1 / f Time taken for any given point on the wave to move a distance of one wavelength, ie the time taken to generate one complete wave. Frequency f = 1 / T Number of crests or troughs that pass a point per second, i e the number of complete waves generated per second. Speed of wave v = fλ Distance moved by a wave per unit time. Wavefront A wavefront is an imaginary line joining all the crests (or all points in phase) on a wave. DARRELL ER (COPYRIGHTED) ©

TRANSVERSE WAVES TRANSVERSE WAVES Definition: Transverse waves are waves whose particles vibrate in a direction perpendicular to the direction of the wave motion. Examples: - Water waves - Electromagnetic waves (learn more in chapter “electromagnetic waves”) - Light waves - Radio waves Particles vibrate in a direction perpendicular to the direction of the wave motion: Notice how the particle is oscillating up & down? The wave, however, is travelling sideways. Hence, the direction of oscillation of the particle is perpendicular to the wave travel. DARRELL ER (COPYRIGHTED) © The is a particle. The blue arrows shows the journey of one particle over time. Over one period*, first it moved down till min amplitude, then up to equilibrium, up again to max amplitude, and down to equilibrium again. one period Time (next instance)

LONGITUDINAL WAVES LONGITUDINAL WAVES Definition: Longitudinal waves are waves whose particles vibrate in a direction parallel to the direction of the wave motion. Examples: - Sound wave - Silky coil Particles vibrate in a direction parallel to the direction of the wave motion: Notice how the particle is oscillating sideways? The wave is also travelling sideways. Hence, the direction of oscillation of the particle is parallel to the wave travel. DARRELL ER (COPYRIGHTED) ©

GRAPHICAL ANAL YSIS DISPLACEMENT- TIME GRAPH DISPLACEMENT- DISTANCE GRAPH ADVANCED CONCEPT DARRELL ER (COPYRIGHTED) ©

DISPLACEMENT - TIME GRAPH DISPLACEMENT-TIME GRAPH A displacement-time graph shows the displacement of a particle as a wave pass through. Just visual this one particle riding a sky drop. Over time, it goes up and down and repeats. KEY ANALYSIS: You can identify the period, T and the amplitude, a from displacement-time graphs. The graph applies to both transverse and longitudinal waves. Direction of displacement will differ. DARRELL ER (COPYRIGHTED) © The is a particle. The blue arrows shows the journey of one particle over time. Over one period*, first it moved down till min amplitude, then up to equilibrium, up again to max amplitude, and down to equilibrium again. one period Time (next instance)