Wave Properties

12.1 THE NATURE OF THE WAVES    Waves transfer energy without transferring matter . We also use waves to transfer information. Examples include a phone and  a radio.  There are many different types of waves.  These include :  sound waves, waves, waves on springs and ropes, and sesimc waves produced  by earthquakes.  All these waves are examples of mechanical waves. Mechanical waves are vibrations which travel  through a medium which is  a substance.   Light waves, radiowaves and microwaves are all examples of  Electromagnetic waves.  When the waves travel through a substance, the substance itself doesn't travel.  You can prove this by observing the waves on a rope. You should see : When a small object is dropped in the , the waves spread out on . The  waves travel through the surface but the does not travel away from the object.  When a tuning vibrates so sound waves travel through the air away from the tuning . The air itself doesn't travel  away from the vibrating object. If it did, a vaccum would be created.    TRANVERSE WAVES  The waves on a rope and the ripples on the surface of are called transverse waves becaue the vibrations ( also called oscillations) move up and down or from side to side. All electromagnetic waves are tranverse waves.  The oscillations of a tranverse waves are perpenducalar to the direction in which the waves transfer energy   LONGITUDINAL WAVES  We can use a splinky spring to demonstrate to how sound waves travel. When one end of splinky  is pushed in and out repeatedly, vibrations travel through the spring. The oscillations are parallel to the direction in which the waves transfer energy. These waves are called longitudinal waves.  Sound waves that travel through the air are longitudinal waves. When  an object vibrates in air,  it makes the air around it vibrate as it pushes and pulls on air. The oscillations (compressions and rarefractions) that travel through the air are sound waves. The oscillations are in the direction in which the wave travels.  The oscillations of a longitudinal wave are parallel to the direction in which the waves transfer energy.  Mechanical waves can be tranverse or longitudinal.      

P12.2 THE PROPERTIES OF WAVES    To find out how engery or information waves carry, you have to measure them.  The ampiltude of the wave is the maximum displacement of a point on the wave from its undisturbed position.  The bigger the amplitude of the waves, the more energy the waves carry.  The wavelength of a wave is the distance from a point on the wave to the equivalent point on the adjacent wave.    FREQUENCY  The number of waves passing a fixed point every second is the frequncy of the waves.  The unit of the frequency is the hertz (Hz) . For the waves on a rope, one wave crest passsing each second is equal to a frequency of 1 Hz.  The period of a wave is the time taken for each wave to pass a fixed point. For the waves of frequncey f, the period T is given by the equation :                                              period, T(seconds, s) = 1/ frequency,f (hertz, Hz)                                        WAVE SPEED A ripple is used to study waves in controlled conditons. You can make straight waves by moving the long edge of a ruler up and down on the surface in a ripple . Straight waves are called plane waves. The waves all move at the same time and stay the same distace apart.  The speed of the waves is the distance travelled by each wave every second through a medium. Energy is transferred at this speed.  For the waves of constant frequency, the spped of the wavs depends on the frequency and the  wavelength.    wave speed = frequency x  wavelength  (metres per second,m/s ) = (hertz, Hz) x (metres, m)  

P12.3 REFLECTION AND REFRACTION    INVESTIGATING WAVES USING A RIPPLE Reflection of waves can be investigated by using a ripple . Each ripple is called the waterfront because it is in the front of each wave as it tavels across the surface. Plane waves. which are produced by repeatedly dipping the long edge of a ruler in , is directed to the metal barrier in the .  These waves are called incident waves to distinguish them from reflected waves. The incident waves are reflected by the metal barrier.    Refraction of waves is the change of direction in which they are travelling when they cross a boundray between one medium and another medium.  You can see this in a ripple when waves cros the boundary between deep and shallow .  EXPLAINING REFRACTION To explain how a wavefront moves foward, imagine that each tiny section creates a wavelet ( a little wave) that travels forward)  The wavelets mover foward together to recreate the wavelength that created them.  REFRACTION When plane waves cross a boundary at a non - zero angle to the boundary, the wavefront experences a change in speed and direction.  The refracted waves have the same frequency but they travel at different speeds, so they have different wavelengths. MATERIALS AND WAVES  When a wave is directed at a substance, some or all of the wave may be reflected at the surface. What happens is dependant on the wavelength of the wave and also on the substance. For example, microwaves are reflected by metal surfaces but they can pass through paper .  The waves that go into a substance, some or all may be abosrbed by the substance. This would heat the substance because it would gain energy from the waves. For example, food is heated in microwave ovens because microwaves are absorbed by the food.  As the waves travel  through a substance, the amplitude gradually decreases because the susbstance absorbs some of the waves' energy.  Waves that are not absorbed by the substance they are travelling through are transmited by it. For example. light is mostly transmitted by ordinary glass but is completely absorbed by darkened glass .       

P12.4 MORE ABOUT WAVES  Sound waves are easy to produce. Vocal cords vivbrate and produce sound waves every time you speak.  any object vibrating in the air makes the layers of air near the object vibrate, which ma