Waves
- Created by: _charmainegalang
- Created on: 06-05-20 16:56
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- Waves
- Properties of waves
- Wave front
- This is an imaginary surface that we draw to represent the vibrating part of a wave.
- If you draw semi-circular sound waves spreading out from a speaker, the semi-circular lines are the wavefront.
- This is an imaginary surface that we draw to represent the vibrating part of a wave.
- Wave front
- Types of waves
- Longitudinal
- Sound waves travelling in air
- Sound waves transfer sound energy
- In a longitudinal wave the oscillations are parallel to the direction of energy transfer
- All longitudinal waves require a medium to travel in eg air, a liquid, or a solid
- This is because they move by particles vibrating
- Sound waves and seismic P waves
- Sound waves travelling in air
- Transverse
- Ripples on the surface of water
- Ripples transfer kinetic energy
- For both ripples on a water surface and sound waves in air, it is the wave that travels and not the water or the air.
- Sound waves transfer sound energy
- For both ripples on a water surface and sound waves in air, it is the wave that travels and not the water or the air.
- Ripples transfer kinetic energy
- In transverse waves, the oscillations are perpendicular to the direction of energy transfer
- Oscillations are up and down but the direction of energy transfer is sideways
- Not all transverse waves require a medium.
- Waves on a water surface, electromagnetic waves and seismic S waves
- Ripples on the surface of water
- Longitudinal
- Measuring wave velocity
- calculating speed of sound in air
- using an echo
- using two microphones and an oscilloscope
- Calculating the speed of ripples on water surfaces
- using a ripple tank and strobe
- calculating speed of sound in air
- Wave equations
- v = f x ?
- ? = wavelength (m)
- f = frequency (Hz)
- v = x/t
- x = distance (m)
- t = time (s)
- v = f x ?
- Waves and boundaries
- Waves can show different effects when they move from one material to another. These changes can occur at the boundary or interface between the two materials
- waves and boundaries
- whenever a sound wave, light wave or water wave reaches the boundary between two materials, the wave can be
- Reflected refracted transmitted or absorbed
- Refraction - waves change direction when they pass from one material to another
- sound waves, water waves and light waves can all be refracted. Refraction can result in a change of both speed and direction. The direction does not change if the wavefronts travel perpendicular to the normal
- Sound waves travel more slowly in cooler, denser air than in warmer less dense air
- Water waves travel faster in deep water than in shallow water. They can also change direction
- Light waves can slow down and change direction when they pass from air to glass
- sound waves, water waves and light waves can all be refracted. Refraction can result in a change of both speed and direction. The direction does not change if the wavefronts travel perpendicular to the normal
- Absorbed -energy of the wave is absorbed by the material. The wave may not pass through the material at all
- Reflected - wave is reflected off the surface of the material
- Transmitted - passing through the material has not changed the wave
- Refraction - waves change direction when they pass from one material to another
- Reflected refracted transmitted or absorbed
- Different substances reflect refract transmit or absorb waves in ways that vary with the wavelength
- Different wavelengths of radiation are absorbed by molecules in the atmosphere by different amounts
- whenever a sound wave, light wave or water wave reaches the boundary between two materials, the wave can be
- Wavelength, absorption and transmission
- Water molecules absorb microwave and infrared wavelength but they transmit radio waves which have longer wavelengths
- Infrared radiation is transmitted by a black plastic bag, bu visible rays are not, as visible rays have a shorter wavelength - they will be absorbed
- waves and boundaries
- Waves can show different effects when they move from one material to another. These changes can occur at the boundary or interface between the two materials
- Sound
- Sound waves travel as particles in the air move from side to side
- These vibrations can pass from one medium to another e.g from air to solid
- Sound waves cannot pass through a vacuum as there are no particles
- Sound waves in the air can trigger vibrations in solids. This only works over a limited range of frequencies
- Human hearing has a frequency range of 20Hz to 20 000Hz
- Frequencies outside of that may not be able to cause the eardrum to vibrate
- High frequency = high pitch
- Low frequency = low pitch
- Small amplitude = quiet sound
- Large amplitude = loud sound
- Frequencies less than 20Hz is known as infrasound
- Frequencies outside of that may not be able to cause the eardrum to vibrate
- Sound waves travel as particles in the air move from side to side
- These vibrations can pass from one medium to another e.g from air to solid
- Sound waves cannot pass through a vacuum as there are no particles
- Human hearing has a frequency range of 20Hz to 20 000Hz
- Just like like light, sound waves can be reflected. we call a reflected sound wave an echo
- Sound waves travel as particles in the air move from side to side
- Ultrasound
- Ultrasound is sound waves with a frequency higher than the upper limit of hearing
- The frequency of ultrasound is at least 20,000Hz
- Ultrasound partially reflects at the boundaries between two different densities
- Ultrasound scanners can produce images of internal orgnas, such as a kidney and the heart
- This works for any organ that is not surrounded by bone
- Ultrasound is also used in industrial imaging
- Ultrasound can be used to detect hidden defects or problems with a weld
- Ultrasound can be used to produce images of a foetus
- Ultrasound scanners can produce images of internal orgnas, such as a kidney and the heart
- Ultrasound is sound waves with a frequency higher than the upper limit of hearing
- Seismic waves
- Internal structure of the Earth
- The outside of the Earth is the solid crust
- The crust is very thin with a maximum depth of around 50km
- There is no way for scientists to directly observe the interior of the Earth
- An earthquake happens due to a sudden movement between the tectonic plates in the earths crust
- This causes seismic waves which carry energy away from the earthquake
- These seismic waves then pass through the earth and they can be detected by seismometers in different countries
- The patterns of these waves give us information about the interior of the Earth
- There are two main types of seismic waves (P waves and S waves)
- P waves are longitudinal waves
- They can pass through both solids and liquids
- P waves travel faster than S waves
- They can pass through both solids and liquids
- S waves are transverse waves
- S waves can only travel through solids
- The parts of the Earth where no S waves can be detected is called the S wave shadow zone
- This is due to the fact that S waves cannot pass through a liquid
- This told scientists that the Earth must contain a liquid core
- This is due to the fact that S waves cannot pass through a liquid
- The parts of the Earth where no P waves can be detected are called P wave shadow zones
- These are due to the fact that P waves travel faster in solids than in liquids
- This means that the P waves slow down as they enter the liquid outer core
- This causes them to refract when they leave the outer core
- This confirms that the outer core is a liquid
- This causes them to refract when they leave the outer core
- This means that the P waves slow down as they enter the liquid outer core
- Sometimes faint P waves can be detected in the P wave shadow zone
- This was used by scientists to show that the Earth also contains a solid inner core
- These are due to the fact that P waves travel faster in solids than in liquids
- P waves are longitudinal waves
- There are two main types of seismic waves (P waves and S waves)
- Seismometers on the Earths surface detect the seismic waves after they have passed through the Earth
- The patterns of these waves give us information about the interior of the Earth
- These seismic waves then pass through the earth and they can be detected by seismometers in different countries
- This causes seismic waves which carry energy away from the earthquake
- An earthquake happens due to a sudden movement between the tectonic plates in the earths crust
- The outside of the Earth is the solid crust
- Internal structure of the Earth
- Properties of waves
- In transverse waves, the oscillations are perpendicular to the direction of energy transfer
- Oscillations are up and down but the direction of energy transfer is sideways
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