Tiêu đề Unit 4 Waves - Cambridge - Dr.Eman Salama.pdf ✅

Unit 4 Waves
Page 120 Unit 4: Waves – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 Unit 4: Waves What are waves?  Waves are a means of transferring energy from one place to another through vibrations without transferring matter. They can be used to transfer information. Types of waves: 1) Mechanical waves: These are waves that require a medium to travel through; they cannot travel through vacuum. e.g. sound waves, ripple waves and slinky spring waves. These waves are either: transverse or longitudinal. 2) Electromagnetic waves: These are waves that do not require a medium to travel through and can travel through vacuum. E.g. Radio waves, X-rays, infrared waves... All electromagnetic waves are transverse.  Waves can be classified according to how the particles vibrate relative to the direction of wave propagation into two categories: 1) Transverse waves: A transverse wave is one that vibrates or oscillates at right angles (perpendicular) to the direction in which the energy or wave is moving. e.g. Electromagnetic waves, water waves and seismic S-waves (secondary). This can be shown by a slinky spring: give one end a quick wiggle at right angles to the spring... the coils of the slinky are vibrating up and down “across” the direction in which the energy is moving “horizontally from left to right”.
Page 121 Unit 4: Waves – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 2) Longitudinal waves: A longitudinal wave is one in which the vibrations or oscillations are along (parallel to) the direction in which the energy or wave is moving. e.g. sound waves & seismic P-waves (primary). Longitudinal waves are recognized by their compressions and rarefactions. This can be shown by a slinky spring: push and pull the end of a slinky in a direction parallel to its axis (give it a quick wiggle to and fro along its length)... the coils of the slinky are vibrating in the directions that are along its length. Describing waves 1. Displacement-distance graph: If you picture a transverse wave (ripple wave) at a particular instant along its length from a side view... you will obtain this displacement-distance graph for the vibrating particles: The graph shows the displacement of the particles along the water surface at a particular instant. Such that: a) When a wave moves through a substance, it causes its particles to move from their equilibrium or resting position. The particle’s distance and direction from its equilibrium position is the displacement. b) The maximum movement/displacement of particles from their resting position caused by a wave is its amplitude (a). This is the height of a wave crest or the depth of a wave trough. It is measured in meters. c) The distance between a particular point on a wave and the same point on the next wave (e.g. from crest to crest with the same displacement and velocity) is called the wavelength (λ).
Page 122 Unit 4: Waves – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 2. Displacement-time graph: If you watch just one vibrating particle and observe how its displacement varies with time as the wave moves... you will obtain this displacement-time graph: a) If a source that is creating a wave vibrates quickly it will produce a large number of waves each second and vice versa. The number of waves produced each second by a source (or the number passing a particular point each second) is called the frequency (ƒ) of the wave. It is measured in Hertz (Hz) where 1 Hz = 1 wave/second. b) The time it takes for a source to produce one wave is called the period (T) of the wave. It is measured in seconds. The frequency and the period are related by the following equation: f = 1 T The Wave Equation The speed of the wave can be known if you know its wavelength and period: speed (v) = distance moved through one wave time of one wave = λ T Since, f = 1 T therefore: v = fλ The speed of a wave depends only on the medium through which the wave is travelling. This means that changing the frequency of a wave within a certain medium does not change its speed within this medium. So for a certain medium, the higher the frequency of wave, the shorter is its wavelength at the same constant speed. The frequency of a wave depends on the source of the wave.