General Wave Properties PDF

General wave properties Subject 1. Types of wave 2. Common features of waves What can be called waves? Create a water wave Create water waves Where else can we find waves? Create a sound wave Create sound waves Wave source Move forwards and backwards. Move u...

General wave properties Subject 1. Types of wave 2. Common features of waves What can be called waves? Create a water wave Create water waves Where else can we find waves? Create a sound wave Create sound 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 qTransverse Waves particles of the medium vibrate at right angle to the direction of motion of the wave Such as: electromagnetic radiation, seismic S- waves qLongitudinal Waves particles of the medium vibrate along the direction of motion of the wave Such as: sound waves, seismic P-waves Questions Q1 Which of the following is not transferred by waves? A matter B information C energy A Questions Q2 Waves can be transverse or longitudinal. a) Describe the difference between transverse and longitudinal waves. b) Give an example of a transverse wave. a) Transverse waves have oscillations that are perpendicular to the direction in which the wave travels. However, longitudinal waves have oscillations that are parallel to the direction in which the wave travels. b) E.g. any electromagnetic radiation/wave, ripples on water, waves on a string, a spring wiggled up and down. Questions Q3 Which two of the following waves are longitudinal? A light B sound C water ripples B Q4 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 qTransverse Waves l A B C crests l D l E F troughs Wavelength (l) - distance from any point to the next exactly similar point. qLongitudinal Waves compression rarefaction l l Displacement-distance graph LAB = 7/4l A B Find the wavelength and the amplitude of wave a and wave b l a=15 cm ? 2 cm 4cm l b=20 cm Measure amplitude and wavelength. Wave the string and find a perfect wave shape. Use your ruler to measure the amplitude and wavelength.  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 Question Q1 What is: a) the amplitude of a wave? b) the wavelength of a wave? c) the frequency of a wave? d) the period of a wave? a) The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed (or rest) position. b) The wavelength is the distance between the same point on two adjacent waves. c) The frequency is the number of waves passing a certain point per second. d) The period is the time taken for one cycle of a wave to be completed.  crest s Wavefront l Wavefront l crests 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 Q2 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 Q1 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 Q2 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= Dt l l （ T） v= = lf 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 = lf Same wave speed Higher frequency(f), shorter wavelength(λ).  l v= = lf T q Frequency (f), period (T) and amplitude (A) are determined by wave source q Speed (v) is determined by the medium q Wavelength (λ) is determined by both wave source and medium