2.6 Waves Flashcards
What is a wave?
A wave is a vibration or osciallation about an undisturbed position
What do waves transfer?
Waves transfer energy and information from one place to another
What do waves NOT transfer?
Matter
What are mechanical waves?
Mechanical waves are vibrations that need a medium to transfer energy.
What are electromagnetic waves?
Electromagnetic waves are oscillations that transfer energy through electrical and magnetic fields and doesn’t need a medium.
Give one example of a mechanical wave
Sound
Give one example of an electromagnetic wave
Light
What are transverse waves?
Transverse waves are waves where the vibrations are perpendicular to the direction of energy transfer
What are longtitudinal waves?
Longtitudinal waves are waves where the vibration is parallel to the direction of energy transfer
Give one example of where transverse waves are found
Ripples on a water surface
Give one example of where longtitudinal waves are found
Sound waves
What properties do longtitudinal waves have?
Longtitudinal waves have areas of compression and rarefaction
Students should be able to describe evidence that, for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels.
- A plastic duck on water will bob up and down, but will not travel with the wave as waves transfer energy, not matter or particles
Define the amplitude of a wave
The amplitude of a wave is from the undisturbed position to the peak.
Define the wavelength of a wave
The wavelength of a wave is the distance from one point of a wave to the equivalent point on the adjacent wave
Define the frequency of a wave?
What is it measured in?
The frequency of a wave is the number of waves passing a fixed point per second
Measured in Hz
Define the period of a wave
The period of a wave is the time taken for a wave to pass a fixed point
Wave Period formula
Period = 1 / frequency
T = 1/f
Period (s), Frequency (Hz)
Define wavespeed
A wavespeed is the speed at which energy is transferred through a medium
Wavespeed formula
wavespeed = frequency × wavelength
v = f λ
Wavespeed (m/s), Frequency (Hz), Wavelength (m)
Describe a method to measure the speed of sound waves in
air
- 2 people must stand 500m away from each other
- When one bangs 2 cymbals together, the other will see them crash together but will not hear it straight away
- Use a stopwatch to time the interval between seeing the impact and hearing the sound
- Repeat the experiment to get an average result
- Use the formula Speed = Distance / Time to calculate the speed of sound in air
Describe a method to measure the speed of ripples on a water
surface
Where can waves be reflected, absorbed or transmitted?
Waves can be reflected, absorbed or transmitted at the boundary between two different materials such as air and water
What happens to waves at the boundary between two materials?
Waves can be reflected, absorbed or transmitted at the boundary between two different materials such as air and water
Describe the effects of the transmission of waves at material surfaces
- Refraction can occur (possibility)
What does the law of reflection state?
The angle of incidence = The angle of reflection
What is the normal?
The normal is a line at 90° to the surface of a material
How are the angle of incidence and angle of reflection measured?
The angles of incidence and reflection are measured between the ray and the normal
What are the most reflective surfaces?
Flat and smoother surfaces are the most reflective
What is specular reflection?
Specular reflection is when light travelling towards a surface is all reflected in a single direction
What is diffuse reflection?
Diffuse reflection is when light is reflected off a rough surface and is scattered in different directions
Why are rough surfaces the least reflective?
Because the light scatters in all directions
What happens when a wave is absorbed?
When a wave is absorbed, the energy of the wave is transferred to the particles of the material
What is transmission?
Transmission is when a wave passes through a substance
Why may a transmitted wave have a lower amplitude?
Because of partial absorption
What are sound waves?
Sound waves are vibrations of air molecules
Why are sound waves longtitudinal?
Sound waves are longitudinal because they transfer energy in the same direction that the air particles vibrate along
How can sound waves travel through solids?
They cause vibrations of particles in the solid
Why do sound waves travel faster in a solid that in a gas?
Because the particles are much closer together so they can pass on the vibrations more easily
Explain how are sound waves detected within the ear?
- Sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound
- The sound waves are converted into vibrations and travel through as vibrations
- The conversion of sound waves to vibrations of solids works over a limited frequency
range, which restricts the limits of human hearing
Why can’t sound waves travel through a vacuum?
Sound waves need a medium in order to travel
What is the range of normal human hearing?
20 Hz to 20 kHz
