Waves Flashcards
In longitudinal waves, is energy transferred parallel or perpendicular to the direction of the vibrations?
Parallel
In transverse waves, is energy transferred parallel or perpendicular to the vibrations?
Perpendicular
How is the wavelength measured in longitudinal waves?
From the center of one compression/rarefaction to the center of the next.
What is the amplitude of a wave?
The distance from the equilibrium position to the crest.
Are EM waves transverse or longitudinal?
Transverse.
Are sound waves transverse or longitudinal?
Longitudinal.
What is the difference between mechanical waves and electromagnetic waves?
EM waves can travel through a vacuum, but mechanical weaves have to travel through a medium.
What is the frequency?
The number of waves that pass a point in one second.
What is the time period?
The time taken for one complete wave cycle.
What is the speed of light?
3x10⁸ m/s
300,000,000 m/s
Why are waves refracted when they hit the boundary of a material at an angle?
- Speed of waves is different in materials with different densities
- Part of the wave hits the boundary between materials first
- Its wavelength increases/decreases and the speed changes
- This changes the direction of the wave
Why are water waves refracted?
They travel slower in shallower water.
What is diffraction?
The spreading out of waves through a gap or around an obstacle.
When do you get the best diffraction?
When the wavelength is a similar size to the gap it is going through.
Why is range of hearing limited?
Converting sound into vibrations through solids only works for a limited frequency range.
What is the auditory range of humans?
20-20,000Hz
How does ultrasound scanning work?
- The waves are partially reflected different amounts by different mediums.
- The reflected waves are detected by a receiver.
Are P-waves longitudinal or transverse?
Longitudinal
They travel faster in solids than liquids.
Are S-waves longitudinal or transverse?
Transverse
Only travel through solids.
Which is more destructive: P-waves or S-waves?
S-waves
They shave building horizontally causing a lot of damge.
Why do waves change direction as they pass through the mantle?
There is a gradual change in density.
What happens to waves at boundarys between the earths layers?
- The waves are refracted.
- There is a large change in density.
What is an S-wave shadow?
The area that receives no S-waves as they are blocked by the liquid outer core.
What are the Em waves in order?
Radio
Microwave
Infra-red
Visible light
Ultra-violet
X-rays
Gamma
Which of the Em waves has the largest wavelength?
Radio waves.
Which of the Em waves has the most energy?
Gamma.
Which of the Em waves has the largest frequency?
Gamma.
Which 3 types of wave are ionising?
- UV
- X-rays
- Gamma
How are radio waves produced?
Oscillations in electrical circuits.
What happens when radio waves are absorbed by an electrical circuit?
They induce an alternating current with the same frequency as the wave
What are radio waves used for and why?
TV and radio transitions
- Large wavelengths (refract around large objects)
- Reflected by the ionosphere (travel long distances)
What are microwaves used for and why?
Microwaves and satellite communication
- Travel through the ionosphere
- Absorbed by water molecules
What are the dangers of microwaves?
Internal tissue heating.
What are infra-red waves used for and why?
Remote controls, heating, night vision
- Warm objects give out more infra-red radiation
What are the dangers of infra-red waves?
Skin burns.
What are visible light waves used for?
Endoscopes (devices that look inside the body) and fiber-optic communication
What are the dangers of visible light waves?
Blindness.
What are ultraviolet waves used for?
Security markings on bank notes
What are the dangers of ultraviolet waves?
Burns and cancer (ionising radiation).
What are X-ray waves used for and why?
medical scanning
- Absorbed only be denser structures
- Show up on film or charge-couple device (CCD)
What are the dangers of X-ray waves?
Cancer (ionising radiation).
What are gamma waves used for and why?
Sterilization and radiotherapy
- The most ionising of the EM waves
What is the name for reflection in a smooth surface?
Specular reflection
What is the name for reflection in a rough surface?
Diffuse reflection
Which direction does light bend when entering more dense material?
Towards the normal.
Which direction does light bend when entering less dense material?
Away from the normal.
What colour light do red objects reflect?
Red light, they absorb all other colours.
How do coloured filters work?
They only let through some colours of light.
What is a perfect black body?
An object that absorbs all radiation incident on it. It is the best possible emitter.
What do hotter objects emmit?
Shorter wavelengths.
How does a light bulb work?
- Current flows through the filament
- Filament heats up
- Thermal emission moves into the visible spectrum
How does the greenhouse effect work?
- Infrared radiation from the sun warms the ground
- The ground emits longer-wavelength infrared
- CO₂ molecules absorb and re-emit the long-wavelength infrared
What are convex lenses?
Converging lenses
What are concave lenses?
Diverging lenses
