6.1 Flashcards
What is the difference between longitudinal and transverse waves?
Transverse waves
- Oscillations are perpendicular to the direction of energy transfer.
- Not all need medium to travel in.
Longitudinal waves
- Oscillations (rarefactions and compressions) are parallel to the direction of energy transfer
- All require medium to travel in.
What are examples of longitudinal waves?
- Sound waves travelling in air.
What are examples of transverse waves?
- ## Ripples on surface of water.
Describe the evidence that when waves are moving, it is the wave that moves, not the medium.
When a wave is moving, the particles in the medium move according to the oscillations of the wave but do not travel across the medium.
Describe wave motion in terms of amplitude.
The maximum displacement of a point on a wave from its undisturbed position.
Describe wave motion in terms of wavelength.
The distance of a point on one wave to the same point on the adjacent wave.
Describe wave mouton in terms of frequency.
The number of waves passing a point each second, in Hz.
Describe wave motion in terms of period.
The time for one wave to pass a point, in seconds.
What is the formula to calculate the speed of a wave?
wave speed (m/s) = frequency (Hz) × wave length (m)
Describe a method to measure the speed of sound waves in air.
- Two people stand at a distance of 500m.
- Person A holds the cymbals. Person B holds the timer.
- Person B starts timing when they see Person A clash the symbols.
- Person B stops the timer when they hear the cymbal.
- Calculate speed of sound wave by doing: distance / time taken.
What are the problems and solutions with the method of measuring wave speed in air?
- Reaction time: have multiple people time the cymbal and remove anomalies to calculate mean.
- Short time: increase distance.
Describe how waves can be reflected absorbed or transmitted at the boundary between two different materials.
- Reflection: wave bounces off surface of material.
- Absorption: wave does not pass through material.
- Transmitted: wave passes through material unchanged.
[Describe how to] Construct ray diagrams to illustrate the reflection of a wave at a surface.
- Draw normal perpendicular to surface from incident ray with direction arrow.
- Measure angle of incidence between incident ray and the normal.
- Since angle of incidence = angle of reflection, draw angle of reflection on the opposite side of normal and draw reflection ray with direction arrow from normal, according to the angle.
[Describe how to] Construct ray diagrams to illustrate where an object image would appear when reflected at a surface.
- Draw incident ray with direction arrow from object to mirror.
- Draw normal perpendicular to mirror and draw reflected ray with direction arrow.
- Repeat this at a different position (preferably above your initial rays).
- Extend the two reflected rays back behind the mirror.
- The object is positioned where the line meet.
Describe how sound waves can be transmitted from one medium to another.
- When waves pass through one medium to another, their speed can change, according to the medium’s density.
- When the wave speed changes the wavelength also changes with it in the same way.
- This results to vibration passing more easily (more dense medium) or less easily (less dense medium).
Describe how the frequency range of human hearing is limited.
Humans can only hear from a range of 20Hz to 20kHz because frequencies above or below these may not cause the ear to vibrate.
Describe how frequency and amplitude affect sound.
- The higher the frequency the higher the pitch.
- The smaller the amplitude the quieter the sound.
What is ultrasound?
Sound waves with a higher frequency that the upper limit of human (‹ 20kHz)
Describe how ultrasound is used for medical imaging.
- Can produce images of internal organs not surrounded by bones.
- Can produce images of foetus.
Describe how ultrasound is used for industrial imaging.
- Can detect hidden defects or problems with a weld.
What is the formula to calculate distances from ultrasound results.
distance (m) = speed (m/s) × time (s)
Example Question:
A ship is using ultrasound to meaure the distance of the sea bed. An ultrasound pulse is emitted. It takes 1.2 seconds for the reflected pulse to return to the ship. Calculate the depth of the sea bed. The speed of ultrasound in water is 1600 m/s.
- Distance from and back to ship: 1.2 × 1600 = 1920 m
- Distance to sea bed: 1920 / 2 = 960 m
What are seismic waves?
P waves:
- Longitudinal waves
- Pass through solids and liquids.
- Faster than S waves.
S waves:
- Transverse waves
- Pass through solid only.
- Slower than P waves.
Describe how seismic wave produce evidence about the internal structure of the Earth.
- S waves travel in curved pathways and had large S wave shadow-zone - Earth has liquid outer core.
- P wave shadow-zones due to change in speed in different densities - Earth has liquid outer core.
- Faint P waves can be detected in P wave shadow-zone - Earth has solid inner core.
What is the device used to detect earthquakes?
Seismometers.
