P6 Waves Flashcards
What is wavelength
The distance from a point on a wave to the equivalent point on. The adjacent one. Measured in meters
What is amplitude?
The maximum displacement of a point on a wave away from its undisturbed position.
What is frequency?
The number of complete waves that pass a point in 1 second.
Measured in Hertz
What is time period?
The time to complete one wavelength
What is a transverse wave?
Particles are at right angles to the direction of the energy transfer. Move up & down. Eg. Water waves
What is a longitudinal wave?
The vibrations of the particles are parallel to the direction of energy transfer. Move left & right
What is compression
Where the particles are closer together
What is rarefaction
When the particles are spread out.
Sound waves
They are longitudinal.
Change in speed of sound waves
When a sound is transmitted across a boundary from one medium to another, it’s speed changes.( frequency stays the same and wavelength changes)
Electromagnetic waves
Microwaves- transfers data to mobile phones
Electric fire- transfers infrared waves to heat us up
Ultraviolet- transferred from the sun
X-Ray machine -transfers X-rays which some of is absorbed by the body.
Radioactive sources- transfer gamma rays
What is an echo?
A reflected sound
Echo sounding
Animals can hear higher frequencies than us. Bats emit pulses of 20000Hz to 100000Hz.
Ships use high frequency sounds to find the depth of the seabed or to locate a shoal of fish.
What is the human sound range?
20Hz to 20KHz
Anything above 20KHz are considered ultrasounds
RP: measuring the wavelength and speed in a ripple tank and waves in a solid.
Use a ripple tank to measure/calculate wavelength and frequency then work out speed.
Use a mechanical vibrator to vibrate a stretched string. To produce a transverse wave. Once the wave is travelling at a steady speed count the wavelength and frequency then calumet the speed.
What is a ray diagram?
Model that shows the number of lines (rays) travelling in a straight line between the wave source and an object or surface. The arrow on the ray shows the direction it is traveling in.
Incident Ray is the one going to the surface and the rejection Ray is the one going away from the surface
What happens when a wave meets a boundary?
It is either reflected, absorbed or transmitted
Law of reflection
When a wave is reflected off a surface, the angle of incidence is equal to the angle of reflection
What is refraction
When a wave changes direction & speed when it enters a different medium.
RP: investigate the reflection of light by different types of surface and the refraction of light by different substances
Specular reflection- all light rays reflected at the same angle
Diffuse reflection- light from one direction is reflected at many different angles.
When light rays enter a denser material, it bends towards the normal.
The angle of reflection should be the same as the angle of refraction.
Speed of sound in different media
Solids are dense so sound travels the quickest in them as the particles are closely packed together.
Uses of ultrasound
Industrial- find cracks/ gaps in aircrafts & measure thickness of objects
Medical- body scans (babies in the womb), measure speed of blood flow in a vein or artery
Why do we use ultra sounds instead of X-rays
Safety- ultrasounds are safe, X-rays are ionising radiation
Imaging- X-rays have high penetrating power so travel through soft tissue, ultrasounds reflect off soft tissue to produce an image
Why do we use gel?
Gel creates a similar frequency so the ultrasound can pass through the skin to get a reflection from soft tissue
What do we use to measure seismic waves?
A seismometers
What are P waves
Is a primary (pressure wave)
Longitudinal waves similar to a sound wave
Speed generally increases with depth in the earth
Can travel through solids and liquids
Slower in liquids than in solids
What is an S wave?
Secondary (shear wave) Transverse wave Speed generally increases with depth in the earth Slower than P waves Can not travel through liquids
P wave shadows zones
Travel through both solids and liquids. As they move through each area, waves are refracted at each layers to create shadow zones
S wave shadow zones
S waves only pass through solids and can not be refracted through the core. Therefore a greater shadow zone is created.
Electromagnetic waves
Are transverse waves
All travel at the speed of light of 3.0 X 10 to the power of 8
Electromagnetic spectrum
Radio waves- longest wavelength Microwaves Infrared radiation Visible light Ultraviolet X-rays Gamma rays- highest frequency and energy
What will happen if you put foil behind a radiator?
Thermal energy will be reflected back. Keeping your house warmer
Refraction of electromagnetic waves
Can be refracted when they enter a medium in which the wave velocity is different. Shorter the wavelength, more the wav refracted.
Amount of refraction can be affected by differences in the atmospheric temperature and pressure.
What is wavefront?
A line that joins all the points on a wave which are moving up and down together at the same time. The wavefront is at right angles to the direction the wave is travelling in.
What are X-rays
They have short wavelengths between 0.1 and 10nm.
Created when high energy electrons suddenly loose energy.
Produced artificially using a X-ray tube
What are X-rays used for?
Imaging- medical and industrial
Security
Treating cancer
Gamma rays
Wavelength between 0.001 and 0.1 nm
What are the uses of gamma rays?
Medical (tracers)
Sterilising food and equipment
Treating cancer (gamma knife)
Industrial imaging
Ultraviolet radiation
Wavelength ranges between 10 to 1000nm
We can’t see it but some animals can
Emitted from the sun
Uses of ultraviolet radiation
Bright clothing- certain chemicals absorb uv radiation and emit it as visible light (high vis)
Security marking- special inks only viable in UV light
Tanning
Helps the skin make vitamin D
Protection from UV light
Cover up Stay in the shade Wear a wide brimmed hat Sunglasses Wear sun cream
RP: investigate the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface
Have cube with hot water in it see which surface emits the most radiation using sensors. Also see which surface absorbs the most radiation
The darker and duller the material the better it is at aborning and emitting infrared radiation
Properties of microwaves
Radio waves with shorter wavelengths
Wavelength= 1mm to 30cm
Less energy with phones than with cooking
Cooking with microwaves
Don’t use flame or heated metal
Quicker and cheaper
Penetrated 1cm into outer layers before being absorbed
Energy transfer makes fat and water molecules vibrate faster
Energy is then transferred from water and fat molecules to centre of the food by conduction
Radar
Uses microwaves to pass through the atmosphere and is reflected back to detect objects in the way of the aircraft
What is an object that transmits light?
Transparent or translucent
Opaque objects don’t let light through
How is the colour of an object determined?
Light can either be aborted or reflected
In a black object all the light is absorbed
In a white object all the light is reflected
In a red object all the light is absorbed apart from the red light which is reflected etc.
Effect of colour filters
Colour filters work by absorbing certain wavelength (colours) and transmitting other wavelengths
Convex lens
Lens is narrow at the purposive and bulges in the middle
Concave lens
Lens is narrow in the middle and the widest at the outside
Principle axis
The horizontal line going through the centre of a lens
Principle focus
Light rays are travelling parallel to the principle axis of a convex lens are refracted to pass through the focus and the light rays are focuses at that point
Real image
Formed by the actual intersection of rays so it can be seen on a screen or other surface placed at the point of intersection
Focal length
The distance from the optical centre of the lens to the focal point/ principle focus
Forming a real image
1 draw a Ray from the object, parallel to the principal axis which refracts through the principal focus (on the other side of the lens)
2 draw a Ray from the object through the optical centre of the lens. This Ray does not change direction.
3 it is helpful to draw a third Ray to confirm the position of the image. Draw a Ray from the object through the principal focus infront of the lens to the lens and then parallel to the principal axis
A perfect black body
An object that absorbs all the radiation that falls onto it. It is also the best emitter of radiation.
Temperature of the earth
Energy entering the earths atmosphere have a shorter wavelength so are more penetrating.
The earth emits radiation as its temperature is higher than that of its surroundings. Although they have a longer wavelength and are less penetrating so some is reflected back to Earth by the atmosphere.
3 main greenhouse gases
Carbon dioxide
Methane
Nitrogen
Changing the earths radiation balance
Changes in human activity
Eg. Burning less fossil fuels & preventing deforestation
