General Wave Properties PDF

General wave properties Subject 1. Types of wave 2. Common features of waves Create a water wave Create water waves Where else can we find waves? Create a sound wave Create sound waves How to make Waves ? Wave source Move forwards and backwards. Move upwards and downward...

General wave properties Subject 1. Types of wave 2. Common features of waves Create a water wave Create water waves Where else can we find waves? Create a sound wave Create sound waves How to make Waves ? Wave source Move forwards and backwards. Move upwards and downwards. Mexican wave  Wave Motion A disturbance transmitted by a medium from one point to another, without the medium itself being transported. 一种由介质从一点传到另一点的扰动， 而介质本身没有被传输。  Particles will return its own position.  Two types of waves ❑Transverse Waves Particles of the medium vibrate at right angle to the direction of motion of the wave Such as: electromagnetic radiation, seismic S- waves ❑Longitudinal Waves Particles of the medium vibrate along the direction of motion of the wave Such as: sound waves, seismic P-waves Questions Which of the following is not transferred by waves? A matter B information C energy A Questions Which two of the following waves are longitudinal? A light B sound C water ripples B Do water waves cause water molecules to travel across the water’s surface? Describe an observation which supports your answer. No. An object will bob up and down on the ripples rather than move across the water. Displacement - distance of an oscillating particle from its equilibrium position. Amplitude (A) - maximum distance from equilibrium position ❑Transverse Waves  A B C crests  D  E F troughs Wavelength () - distance from any point to the next exactly similar point. ❑Longitudinal Waves compression rarefaction   Displacement-distance graph LAB = 7/4 A B Find the wavelength and the amplitude of wave a and wave b  a=15 cm ? 2 cm 4cm  b=20 cm  Displacement A cycle 0 T 2T Time Period (T ) - time taken to complete a cycle of oscillation time taken to move forward by one wavelength Displacement No. of cycles 0 Time Unit time (1s) Frequency (f ) - no. of complete cycles performed per unit time. f = 1/T Displacement/cm Can you find the wavelength in this graph? 5 NO ! 0 3 6 9 Time/s 12 -5 Amplitude A = 5 cm Period T = 6 s Frequency f = 1/T = 1/6 Hz Wavefront  Wavefront A displacement time Movement of point A  Displacement-time graph Displacement- distance graph shows how the displacement of a single particle in the wave varies with time. Question What are wavefronts? Wavefronts are imaginary lines drawn through identical points on waves, e.g. through each crest. They’re perpendicular (at right angles) to the direction in which the wave is moving. Question The diagram below shows a man shaking a spring up and down to produce a wave. What is the wavelength of the wave? 2 × 2.0 = 4.0 m Question An oscilloscope is used to display the wave below. a) What is the amplitude and the period of the wave shown? a) Amplitude = 1.0 cm, Period = 4.0 s b) Calculate the frequency of the wave. f = 1 ÷ T = 1 ÷ 4.0 = 0.25 Hz Displacement TRED = 2TGREEN Time TGREEN 2fRED = fGREEN Wave speed (v) distance the wave moves per unit time. Distance x （time Δt） x v= t   （ T） v= = f T Example A water wave is generated by a wave machine in a pool. The wave travels to the end of the pool, is reflected, and travels back to the wave machine. It takes 8.0 seconds for the wave to return to the machine once it has been generated. The wave travels at a speed of 4.5 m/s. How far from the end of the pool is the wave machine? x = v × t = 4.5 × 8.0 = 36 m 36 ÷ 2 = 18 m A transverse wave travelling with an amplitude of 5 cm (A) has a frequency of 10 Hz. The horizontal distance from (f) a crest to the nearest trough is measured to be 2.5 cm. Half wavelength (1/2λ) Find the period of the wave and speed of the wave. (T) (v) T = 1/f = 1/10 Hz = 0.1 s v = λf = 2× 2.5 cm×10 Hz = 50 cm/s = 0.5 m/s  v = f Same wave speed Higher frequency(f), shorter wavelength(λ).   v= = f T ❑ Frequency (f), period (T) and amplitude (A) are determined by wave source ❑ Speed (v) is determined by the medium ❑ Wavelength (λ) is determined by both wave source and medium