Waves Flashcards
(31 cards)
What’s the difference between transverse and longitudinal waves?
In transverse waves, the oscillations are perpendicular to the direction of energy transfer.
In longitudinal waves, the oscillations are parallel to the direction of energy transfer.
What are the 2 types of waves?
Waves may be either transverse or longitudinal.
What wave is a ripple?
Transverse.
What do longitudinal waves have?
Longitudinal waves show areas of compression and rarefaction.
What wave is sound?
Sound waves travelling through air are longitudinal.
What is evidence that waves do not transfer matter?
1) Objects floating on water
- Objects floating on water will stay in the same place, only bobbing up and down, unless the water moves.
2) Particles in the water or air vibrate
- The particles in the water or air vibrate and transfer energy, but they do not move with the wave. For example, if you place a cork in a tank of water and create ripples, the cork will bob up and down but will not move across the tank.
3) Vibrating drum skin
- A vibrating drum skin does not move the air away to create a vacuum around the drum.
4) Loudspeaker
- A loudspeaker does not cause a gust of wind
What are waves?
Waves transfer energy from one place to another without transferring any matter.
What is amplitude?
The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.
What is wavelength?
The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.
What is frequency?
The frequency of a wave is the number of waves passing a point each second.
What is period?
The time it takes for one wave cycle to complete. It’s measured in seconds.
What is wave speed?
The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
Can you identify amplitude and wavelength from given diagrams?
Can you?
Describe a method to the speed of sound in air:
1) Attach a signal generator to a speaker to generate sounds with a specific frequency
2) Use two microphones and an oscilloscope to find the wavelength of the sound waves generated
3) Set up the oscilloscope so the detected waves at each microphone are shown as separate waves
4) Start with both microphones next to the speaker, then slowly move one away until two are aligned on the display, but have moved exactly one wavelength apart
5) Measure the distance between the microphones to find one wavelength
6) Use formula v=fλ to find the speed of the sound waves passing through the air - the frequency is whatever you set the signal generator to
7) The speed of sound in air is roughly 330m/s so make sure results are similar
Describe a method to measure the speed of ripples on a water surface:
1) Use a signal generator attached to the dipper of a ripple tank to create water waves at a set frequency
2) Use a lamp to see wave crests on a screen below the tank and make sure the size of the waves’ shadows are the same size as the waves
3) Take a photo of the shadows and ruler and find the wavelength from the photo
4) The distance between each shadow line is equal to one wavelength so measure the distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find the average wavelength - this is a good method to measure small wavelengths
5) Use v=fλ to calculate wave speed of the waves
Identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid and take appropriate measurements:
This is a suitable set-up as it allows you to measure the wavelength without disturbing the waves.
Show how changes in velocity, frequency and wavelength, in transmission of sound waves from one medium to another, are inter-related?
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.
At a boundary, what happens to waves?
Waves can be reflected at the boundary between two different materials.
Waves can be absorbed or transmitted at the boundary between two different materials.
Can you construct ray diagrams to illustrate the reflection of a wave at a surface?
Can you?
Remember:
1) Angle of incidence
2) Angle of reflection
3) Normal
4) Incoming ray
5) Reflected ray
6) Point of incidence
7) Boundary
This is all on page 75
Describe the effects of reflection, transmission and absorption of waves at material interfaces:
1) Reflection
- Waves bounce off the surface of an object. The amount of reflection depends on the surface’s smoothness and flatness. Flat, smooth surfaces reflect the strongest waves, while rough surfaces scatter light in all directions and reflect the least.
2) Transmission
- Waves pass through a material. For example, light waves can pass through air, water, and glass. The more transparent the material, the more light will pass through.
3) Absorption
- Waves transfer their energy to the particles of a substance, increasing the material’s internal energy. For example, the Earth’s surface absorbs infrared radiation from the sun. Waves can be absorbed partially or completely.
The effects of these interactions depend on the properties of the wave, the difference between the two materials, and the densities of the materials. For example, light will be absorbed if its frequency matches the energy levels of the electrons in the material.
Describe an investigation of the reflection of light by different types of surface and the refraction of light by different substances:
1) Take a piece of paper and draw a straight line across it. Place an object so one of its sides lines up with this line.
2) Shine a ray of light at the object’s surface and trace the incoming and reflected light beams
3) Draw the normal at the point where the ray hits the object. Use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table. Also make a note of the width and brightness of the reflected light ray
4) Repeat this experiment for a range of objects
You should see that smooth surfaces cause specular reflection to give clear reflections - the reflected ray is as thin and bright as incident ray. Rough surfaces cause diffuse reflection which makes the reflected ray to be wider and dimmer.
The angle of incidence = the angle of reflection
Can sound waves travel through solids?
Sound waves can travel through solids causing vibrations in the solid.
How do we hear sound?
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range. This restricts the limits of human hearing.
Describe processes which convert wave disturbances between sound waves and vibrations in solids:
Sound waves reach the ear drum and cause the ear drum to vibrate. These vibrations are passed onto tiny bones in your ear called ossicles, through the semi-circular canals and to the cochlea. The cochlea turns these vibrations into electrical signals which get sent to your brain and allow you to sense the sound. Different materials can convert different frequencies of sound waves into vibrations. For example, humans can hear sound in the range of 20 Hz - 20 kHz. Microphones can pick up sound waves outside of this range but you wouldn’t hear anything.
