Topic 4 Waves

• Waves transfer energy and information from one place to another without transferring matter.
• Particles of water or air vibrate and transfer energy but do not move with the wave. This can be shown by placing a cork in a tank of water and generating ripples across the surface. The cork will bob up and down on the oscillations of the wave but will not travel across the tank.
• Frequency is the number of waves passing a point per second. It is measured in Hertz (Hz)
• The wavelength of a wave is the distance from a point on one wave to a point in the same position on the next wave measured in metres
• The period is the length of time it takes one wave to pass a given point
• the amplitude of a wave is the maximum distance from a point on the wave away from its rest position

  
• the velocity of a wave is the speed of the wave in the direction it is travelling
• Wavefronts An imaginary surface representing points of a wave that are at the same point in their cycle

  
• Transverse waves are waves where the vibrations are at right angles to the direction of the wave.
• Longitudinal waves are waves where the vibrations are parallel to the direction of the wave.
• Transverse waves examples: water waves, some seismic waves, electromagnetic waves
• Longitudinal waves examples : Sound waves and some seismic waves
• wave speed (m/s) = frequency(Hz)* wavelength(m)
• wave speed(m/s) = distance (m)/time (s)
• Measure the speed of sound waves by measuring the time it takes for a sound to travel a certain distance, the speed can be calculated using s=d/t
• One way of measuring the speed of waves on water is to measure the time it takes for a wave to travel between two fixed points . Speed can be calculated using s = d/t
• calculate depth or distance from time and wave velocity
• reflected - wave bounces off
• refracted - wave passes into the new material but changes the direction in which is in travelling
• transmitted the wave passes through the material and is not absorbed or reflected
• absorbed- the waves disappears as the energy it is carrying is transferred to the material
• When a wave crosses a boundary between materials at an angle it changes direction which means it's refracted 
• Waves crosses a high density material will have a slower wave and wave crossing low density material will have a higher speed 
• Depending on how much the wave speeds up or slows down will affect how much the wave is refracted.
• If a wave crosses a boundary and slows down it will bend towards the normal. If it crosses into a material and speeds up it will bend away from the normal 
• . The wavelength of a wave changes when it is refracted, but the frequency stays the same 6. If the wave is travelling along the normal it will change speed, but it's not refracted
• different substances may absorb, transmit, refract or reflect waves in ways that vary with wavelength
• wave disturbances are any action that cause something to sound/vibrate (same thing)when something vibrates (say after hitting a drum), the particles vibrate then hit the air particles which then like a domino result in the air particle layer above to vibrate. the air particles continue to vibrate until they reach the bones in your ear where they vibrate to process the sound. when you put your head on the surface that vibrates it is louder bc it doesnt have to travel through the air
• sound with frequencies greater than 20,000 Hz is known as ultrasound
• sound with frequencies less than 20Hz is known as infrasound
• Sonar equipment carried on ships find the depth of the sea by emitting a pulse of ultrasound and times how long it takes for the sound to return
• ultrasound can also be used to make images inside the body. one common use it to make detailed images of unborn babies
• Nature produces infrasounds in the form of seismic waves. By analysing how these are absorbed and reflected by the inside of the planet, scientists have been able to work out the internal structure of the earth.
• he human ear detects sound. The outer ear, which is also known as the pinna, funnels the sound into the ear canal. Sound waves travel along the ear canal and cause the eardrum to vibrate. Three small bones transmit these vibrations to the cochlea. This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.
• When sound moves from a less dense medium to a denser medium: The wavelength of the sound wave increases. The frequency of the sound wave stays the same. The velocity of the sound wave also increases.