Waves (Seneca) Flashcards
Waves transfer energy from …
one place to another without transferring matter.
Wave motion (the movement of waves) can be shown by the …
vibrations of a spring or by water waves.
When a wave travels along the surface of the water, a cork floating on the surface of the water will only …
move up and down as the wave passes.
Wave speed =
frequency × wavelength
Frequency of a wave =
1 / time period
Wave frequency =
number of oscillations / time
number of oscillations / time
= wave frequency
The amplitude of a wave is the …
largest distance that a point on the wave moves from its rest position.
The wavelength is the …
distance between two adjacent wavefronts.
A transverse wave causes the particles in the medium (the substance that the wave travels through) to …
vibrate at right angles to the direction of the wave’s motion.
At what angle do the particles move relative to a transverse wave’s direction?
90 degrees (right angle)
Examples of longitudinal waves are …
sound waves
In what position do particles end up after a transverse wave has passed?
Same position
Water waves can be set up in a ———- , where a rod at one end of a tank of water creates a series of ripples.
Ripple Tank
Water waves can be set up in a Ripple Tank, where a …
rod at one end of a tank of water creates a series of ripples.
bright light shone through the water onto a sheet of paper shows the ripples on the water very clearly as a series of parallel lines travelling along with constant speed.
These parallel lines are the peaks of the ripples on the water. We call them …
wavefronts
What is the distance between two wavefronts?
Wavelength
The wave speed (metres per second, ms-1) of a wave is equal to …
its frequency (Hertz, Hz) multiplied by its wavelength (metres, m).
A longitudinal wave causes the medium’s particles to …
vibrate in the same direction as the wave’s motion.
Here are some example of longitudinal waves:
- Sound waves
- P-waves
A bright light shone through the water onto a sheet of paper shows the ripples on the water very clearly as a series of ———— lines travelling along with constant speed.
parallel
When waves travel from one medium to another, their speed and wavelength change but their ——— stays the same.
frequency
When waves travel from one medium to another, their ————- change but their frequency stays the same.
speed and wavelength
The speed of a wave changes when it travels from …
one medium to another.
The ——— of a wave also changes when it travels from one medium to another.
wavelength
The speed and the wavelength are …
directly proportional.
If the speed doubles, the wavelength …
doubles
If the speed halves, the wavelength…
halves.
The frequency of the wave does not change because …
the source is producing the same number of oscillations (vibrations) per second.
Waves can be ————- at the boundary between one medium (material) and another.
reflected, refracted, absorbed and transmitted (passes through)
If the wave crosses to the new medium at an angle (not 90 degrees), the change in the wave’s speed will …
cause the direction of the wave’s motion to change and the wave will appear to bend.
If the wave crosses to the new medium at an ————- , the change in the wave’s speed will cause the direction of the wave’s motion to change and the wave will appear to bend.
angle (not 90 degrees)
If the wave crosses to the new medium at an angle (not 90 degrees), the change in the wave’s speed will cause the direction of the wave’s motion to change and the wave will appear to bend.
This is called …
refraction
Reflection happens when a …
wave hits a flat surface (plane) and bounces off.
What is transmission?
Waves carry on travelling through a new material.
This often leads to refraction.
What is absorption?
When waves meet some materials, the energy is absorbed by the material.
What type of material absorbs the most light?
Matte black
The angle of incidence is the …
angle between the incident (incoming) light ray and the normal.
The normal is a …
line at 90 degrees to the plane.
Light can be reflected by a …
plane (flat surface).
The angle of reflection is the …
angle between the reflected light ray and the normal.
The law of reflection states that …
the angle of incidence = the angle of reflection.
Light is refracted when it travels from …
one medium to another and changes speed.
If light speeds up on entering a new medium, this medium is “—————”.
less optically dense
If light speeds up on entering a new medium, this medium is “less optically dense”.
The light is refracted ———— from the normal - the angle of refraction is larger than the angle of incidence.
further
If light speeds up on entering a new medium, this medium is “less optically dense”.
The light is refracted further from the normal - the angle of refraction is ——— than the angle of incidence.
larger
If light speeds up on entering a new medium, this medium is “—————-”.
The light is refracted further from the normal - the angle of refraction is larger than the angle of incidence.
less optically dense
What will happen to the wave if the light enters a less optically dense material?
It will speed up
Light speeds up when …
entering a less optically dense medium.
Light speeds up when entering a less optically dense medium. When this happens, some light is …
refracted and some light is reflected.
What is internal
reflection?
when some light is refracted and some light is reflected
What is angle of
refraction?
The angle between the refracted light and the normal.
If the angle of incidence is the same as the critical angle, the light will …
travel along the boundary of the 2 mediums.
If the angle of incidence is the ——- as the critical angle, the light will travel along the boundary of the 2 mediums.
same
If the angle of incidence ——— the critical angle, then all the light will be reflected. This is called total internal reflection.
exceeds
If the angle of incidence exceeds the critical angle, then ———— . This is called total internal reflection.
all the light will be reflected
If the angle of incidence exceeds the critical angle, then all the light will be reflected. This is called …
total internal reflection.
Total internal reflection means that …
all of the light is reflected and no light is refracted.
If the angle of incidence is the same as the critical angle, the light will …
travel along the boundary of the two mediums.
Sound waves are ————— waves.
longitudinal
Sound waves are longitudinal waves. They can travel through solids by …
causing vibrations in the solid.
Sound is produced by the …
vibration of particles in a medium (the substance that waves travel through).
The vibrations mean that sound waves travel in a series of …
compressions (where the medium is squashed together) and rarefactions (where the medium is stretched apart).
Ultrasound has a frequency …
above 20,000Hz.
Our ears can detect vibrations (compressions and rarefactions) and transfer the information to our brain via our …
auditory nerve.
Our ears are sensitive to (can hear) a range of frequencies between …
20Hz and 20,000 Hz.
Ultrasound has a frequency above 20,000Hz. Humans cannot hear sounds with frequencies this high, but ————- can.
other animals
Dog whistles have frequencies above 20,000Hz, which is why …
humans cannot hear them.
Ultrasound is also used by …
doctors to perform scans of a developing foetus.
The range of frequencies that we can hear changes with age.
Elderly people tend to become …
less sensitive to sounds with a higher frequency.
Sound needs to travel through a …
medium
The more rigid the medium is, the ——— the speed of the sound wave through the medium.
higher
The ——— rigid the medium is, the higher the speed of the sound wave through the medium.
more
The more compressible the medium is, the ——- the speed of the sound wave through the medium.
slower
The ——- compressible the medium is, the slower the speed of the sound wave through the medium.
more
Gases are ————- , so the speed of sound in a gas is very slow.
readily compressible (easy to squash)
Gases are readily compressible (easy to squash), so the speed of sound in a gas is …
very slow.
Solids are significantly ———— and gases and are very hard to compress.
more rigid than liquids
Solids are significantly more rigid than liquids and gases and are very hard to compress.
Therefore, the speed of sound in solids is much …
higher than in liquids or gases.
Liquids are more ————— than gases, so the speed of sound in liquids is much higher than in gases.
rigid and less compressible
Liquids are more rigid and less compressible than gases, so the speed of sound in liquids is …
much higher than in gases.
——— can be used to measure the speed of sound.
Echoes
Describe the experiment for Measuring the Speed of Sound. (Short)
Two people stand a measured distance from a tall vertical wall. This distance should ideally be about 100m.
The first person bangs two wooden blocks together to make a sharp sound and repeats this every time the echo is heard. Starting counting from zero, the second person uses a stopwatch (timer) to measure the time taken for a number of claps – 50 or 100.
In the time between two successive claps, the sound travels to the wall and back.
The speed of sound can be calculated from the following relationship:
speed of sound = ( distance to wall × 2 × number of claps (N)) ÷ time taken for N claps.
Sound is a wave. Because of this, it can be:
- Absorbed
- Transmitted
- Reflected
- Refracted
When ultrasound waves meet a boundary between two different materials, some are reflected. We can work out how far away a boundary is based on …
how long it takes for reflections to reach a detector.
We can use ultrasound waves for both …
medical and industrial imaging.
Ultrasound uses:
- training dogs (dog whistles)
- industry
- measuring water depth
- medicine
Doctors use ultrasound to …
perform scans of a developing foetus.
Ultrasound waves can ———- the body.
pass through
Whenever they reach a boundary between two different materials, some will be reflected. We can detect the …
reflected waves
Whenever they reach a boundary between two different materials, some will be reflected. We can detect the reflected waves.
A computer processes the …
timing and distribution of these waves. The computer uses these to produce a video image of the foetus.
We can use echo sounding to …
detect objects in deep water and also to measure water depth.
We can use ———- to detect objects in deep water and also to measure water depth.
echo sounding
We send an ultrasound pulse into the water. When this pulse hits any surface, it is …
reflected back.
We can work out the distance travelled by the sound wave by …
recording the time between us sending the pulse and detecting the reflection.
We can use ultrasound in industry to …
find flaws in objects or materials (e.g. pipes or wood).
When ultrasound waves enter a material, they will normally be reflected by the far side of the material.
If there is a flaw (e.g. a crack), the waves will …
be reflected sooner. This tells us that there is a problem.
Earthquakes produce two types of seismic waves:
- P-waves (primary)
- S-waves (secondary)
Seismic waves are …
waves which travel through the Earth.
P-waves are …
longitudinal, seismic waves.
P-waves travel at …
different speeds through solids and liquids.
S-waves (secondary) are …
transverse, seismic waves.
S-waves cannot travel through …
liquids (only through solids).
Seismic waves cannot travel through all parts of the earth because …
the earth is made up of different materials.
Seismic waves cannot travel through all parts of the earth because the earth is made up of different materials.
Scientists have used this principle to …
work out the different materials that the earth is made up of.
By detecting seismic waves from Earthquakes, scientists have worked out that …
the Earth has a solid core surrounded by a liquid outer core.
In a sound wave, in which direction do the particles move?
In the same direction as the wave’s motion.
When light moves into a less optically dense medium, what happens?
- the light speeds up
- the angle of refraction is greater than the angle of incidence
If the incident light is at the critical angle, what will the refracted light do?
Travel parallel to the boundary of the two mediums.
All electromagnetic waves are ——— waves that travel at the same speed (or velocity) in a vacuum.
transverse
All electromagnetic waves are transverse waves that travel at …
the same speed (or velocity) in a vacuum.
All electromagnetic waves are transverse waves that travel at the same speed (or velocity) in a vacuum. To simplify things, we assume that the speed of electromagnetic waves in …
air is the same as that in a vacuum.
There is a continuous spectrum of EM waves and the waves transfer …
energy from the source to the absorber of the wave.
what is the anagram to remember em waves?
roman
men
invented
very
useful
x-ray
guns
what ,in order of lowest to highest frequency, is the em spectrum?
radio
microwave
infrared
visible light
ultraviolet
x-ray
gamma
As you move from gamma rays to radio waves, the wavelengths increase and the frequencies …
decrease
As you move from gamma rays to radio waves, the wavelengths ————– and the frequencies decrease.
increase
Gamma rays have the shortest wavelength and the ———frequency.
highest
Gamma rays have the ——–wavelength and the highest frequency.
shortest
Radio waves have the ———– wavelength and the lowest frequency.
longest
Radio waves have the longest wavelength and the ——— frequency.
lowest
Gamma rays also carry the ———– amount of energy than any other wave in the electromagnetic spectrum.
most
Wave energy ———– with frequency.
increases
Wave energy ———- with wavelength.
decrease
Gamma rays are used for …
medical imaging and therapy, astronomy, sterilisation and food preservation.
Gamma rays are extremely ———————- to living tissues and cells.
penetrating and damaging
Gamma rays carry the most energy. We can use gamma rays to destroy …
bacteria and tumours.
X-rays penetrate …
soft materials (like body tissue).
Bones are —— materials that absorb X-rays.
dense
Bones are dense materials that ——– X-rays.
absorb
Bones are dense materials that absorb X-rays. We can use X-rays to …
build a shaded image of bones and body tissue.
Low-energy X-rays are used for …
medical and industrial imaging.
High-energy X-rays are used to …
treat cancer.
X-rays are also used for …
security purposes to detect weapons in airports (and other places).
A risk of X-rays are that they are …
highly ionising (can damage body cells), even in low doses.
Due to the dangerous nature of X-rays, exposure to X-rays should always be kept to a …
minimum
People working with X-ray equipment should always …
shield themselves to prevent exposure to X-rays.
People working with X-ray equipment should always shield themselves to prevent exposure to X-rays.
These people will …
place materials (metals like lead) between themselves and the X-rays.
Ultraviolet light is used in …
medical and forensic photography, air purification, disinfection and medical therapy.
Ultraviolet light can also be used to …
detect fake bank notes.
Exposure to too much ultraviolet light can cause …
skin burns, skin cancer and cataract formations in the eye.
In lamps, UV photons ——– atoms. The atoms then release visible light.
excite (gives energy to)
In lamps, UV photons excite (gives energy to) atoms. The atoms then …
release visible light.
In lamps, UV photons excite (gives energy to) atoms. The atoms then release visible light.
In sun tanning, UV excites …
(gives energy to) skin cells. The skin cells then change colour.
In lamps, UV —— excite (gives energy to) atoms. The atoms then release visible light.
photons
One of the risks of Infra-red radiation is that it can cause …
serious skin burns if emitted from high-intensity sources.
Infra-red radiation is used in …
TV controls.
Infra-red can also be used for …
security purposes, such as in intruder alarms by detecting body heat.
Infra-red cameras can detect a …
range of frequencies. These frequencies can be shown in different colours to depict images.
We should always —— any exposure to microwaves.
reduce
As with X-rays, microwaves always have —————— between the source of microwaves and living tissue.
some sort of shielding
Microwaves have a —————– to penetrate the Earth’s atmosphere and to reach satellites.
high enough frequency
Microwaves have a high enough frequency to …
penetrate the Earth’s atmosphere and to reach satellites.
Microwaves travel in straight lines through the atmosphere. This makes them good for …
transmitting (sending) signals.
Microwaves travel in —————– through the atmosphere. This makes them good for transmitting (sending) signals.
straight lines
Microwaves are absorbed by water, heating up the water in the process. This makes microwaves useful for …
cooking food because food contains lots of water.
Microwaves are absorbed by water, ———– in the process. This makes microwaves useful for cooking food because food contains lots of water.
heating up the water
Microwaves are ——– by water, heating up the water in the process. This makes microwaves useful for cooking food because food contains lots of water.
absorbed
Microwaves are also used to transmit signal from a …
nearby phone mast (transmitter) to a mobile phone.
Microwaves are used for the purpose of ———— communications (transmitting signals between stations on Earth and satellites).
satellite
Because humans are ————-, exposure to microwaves could have a harmful effect.
largely made up of water
Radio waves are used for …
radio and TV communications.
Because radio waves have ————— , they can be transmitted (sent) around the Earth’s surface and around buildings without interference.
long wavelengths
Because radio waves have long wavelengths, they can be …
transmitted (sent) around the Earth’s surface and around buildings without interference.
At high intensities, radio waves can cause …
internal heating of living tissue with potentially harmful effects.
Electromagnetic waves can be produced by …
electrical circuits and by changes in atoms.
Oscillations (repeating variations) in electrical circuits can produce …
radio waves.
——— in electrical circuits can produce radio waves.
Oscillations (repeating variations)
When radio waves are absorbed, they can create an …
alternating current with the same frequency as the radio wave itself.
When radio waves are absorbed, they can create an alternating current with the same frequency as the radio wave itself.
This means that …
radio waves can lead to oscillations in an electrical circuit.
Changes in atoms and the nuclei of atoms can result in electromagnetic waves being …
generated or absorbed over a wide frequency range.
Changes in atoms and the nuclei of atoms can result in ———— waves being generated or absorbed over a wide frequency range.
electromagnetic
Gamma rays originate from …
changes in the nucleus of an atom.
Electromagnetic radiation can be produced by:
- changes in atoms
- electrical circuits
We use visible light in ———- because it can be totally internally reflected.
optical fibres
We use visible light in optical fibres because …
it can be totally internally reflected.
We use visible light in optical fibres because it can be totally internally reflected.
This means that we can …
transmit signals (information) along optical fibres without the signals (information) getting lost.
We use visible light to …
see the world around us and in fibre optics.
Traditionally, we say that there are seven colours of light in the spectrum :
Red, Orange, Yellow, Green, Blue, Indigo and Violet.
Transparent objects also transmit light without …
scattering the rays.
Opaque objects either ———- all light that hits them.
reflect or absorb
Translucent objects transmit light but the rays are …
scattered.
Light can be reflected from a surface in two ways :
- Diffuse reflection
- Specular reflection
Diffuse reflection happens when …
light is reflected by a rough surface.
Specular reflection happens when …
light is reflected by a smooth surface in a single direction.
Each colour within the visible light spectrum has its own …
narrow band of wavelength and frequency.
If all wavelengths are reflected equally, the opaque object looks …
white.
If all wavelengths are absorbed, the object looks …
black.
When an opaque object looks like it has a particular colour, it is …
reflecting light of that particular wavelength (colour) and absorbing all other wavelengths.
Colour filters absorb …
certain wavelengths (colours) and transmit other wavelengths (colours).
Objects appear as different colours based on …
how the colours of white light are absorbed and reflected.
If a blue book was looked at through a red filter, the book would look black.
This is …
because the red filter will only allow red light to pass through.
It will absorb all other colours of light.
A blue book looks blue because …
every colour from the visible light spectrum is absorbed except for the colour blue, which is reflected.
An —– sends pulses of high frequency sound waves.
emitter
A lens forms an image by …
refracting light.
There are two main types of lens:
concave and convex.
A convex lens is …
curved on both sides and is wider at the middle than at the edges.
The principal focus of a convex lens is the …
place where all the rays hitting the lens parallel to the axis meet.
The distance from the lens to the principal focus is called the …
focal length.
A convex lens is also called a …
converging lens.
A concave lens is …
wider at the edges than in the middle.
When parallel rays of light enter a concave lens, they …
disperse (spread out).
In concave lens, if you trace back along the paths of the dispersed rays, they will look like …
they came from the principal focus that is behind the lens.
A concave lens is also called a …
diverging lens.
Which lens is wider in the middle and thinner at the ends?
Convex
Which lens is thinner in the middle and wider at the ends?
concave
Convex lenses produce images that are either …
real or virtual.
Concave lenses only produce
—— images.
virtual
A virtual image appears on the …
same side of the object
We cannot project virtual images onto a …
screen.
Convex lenses produce images that are …
either real or virtual.
A real image appears on the ——— to the object.
other side of the lens
A virtual image appears on the same side of the object. We cannot project virtual images onto a …
screen.
We can use this equation to calculate the magnification a lens produces:
magnification = image height ÷ object height
Magnification is a ratio. It has no …
units.
What type of image can we project on to a screen?
real
When drawing ray diagrams:
- Draw the principal axis (the horizontal line that goes straight through the middle of the lens).
- Use the correct lens symbols.
- Mark the principal focus on either side of the lens.
- Draw a dot on the principal axis and label it F.
- Mark the position of the object as an arrow standing on the principal axis.
- Now draw the light rays.
what anogram is used to remember the steps for drawing ray diagrams?
Don’t
Use
Mark
Draw
Maps
Never
How do you Draw a Convex Lens Ray Diagram?
Draw a line from the top of the object to the lens.
From this point on the lens, draw a second line through the principal focus on the other side of the lens.
Draw a third line from the top of the object straight through the middle of the lens.
If the lines meet on the opposite side of the lens, this forms a real image.
Draw the image as a vertical arrow connecting the point where the lines cross to the principal axis.
If the lines do not meet (diverging rays), this forms a virtual image.
What is the anogram you use for Drawing a Convex Lens Ray Diagram?
Draw
from
Destiny
if
dogs
infer
How do you Draw a Concave Lens Ray Diagram?
Draw a straight line from the top of the object to the lens.
Draw a dotted line from the principal focus (on the same side of the lens) to the point where the first line meets the lens.
Continue the second (dotted line) through the lens as a solid line.
Draw a third line from the top of the object through the middle of the lens.
The top of the image (virtual and the right way up) is where the dotted line meets the third line.
Draw a vertical arrow on this image from the principal axis to where the lines meet.
what is the anogram for How to Draw a Concave Lens Ray Diagram?
Don’t
Dry
Cats
Do
the
Dance
What is the name of the horizontal line that goes straight through the middle of the lens?
principal axis
In convex ray diagram, light rays …
focus to a point.
In concave ray diagram, Light rays …
spread out.
Infrared radiation can transfer thermal energy without a …
medium (substance to travel through).
All bodies (objects) emit …
radiation.
The ———— emitted by the Sun transmits thermal (heat) energy to the Earth.
infra-red radiation
Infra-red radiation does not need a medium, so can still travel through …
space.
Surfaces can either ————————– infra-red radiation.
reflect, absorb (take in), or emit (give out)
Black surfaces are good emitters, —— absorbers and poor reflectors.
good
Black surfaces are good emitters, good absorbers and ——— reflectors.
poor
Black surfaces are ——– emitters, good absorbers and poor reflectors.
good
White surfaces are ——— reflectors of infra-red radiation.
good
White surfaces are —- emitters and absorbers of infra-red radiation.
poor
Shiny surfaces of a colour are ———- absorbers of radiation than dull surfaces of the same colour.
poorer
Shiny surfaces are ————— emitters and better reflectors than dull surfaces of the same colour.
poorer
A perfect black body is an object that …
absorbs all of the radiation incident on it.
A black body does not …
reflect or transmit any radiation.
Since a good absorber is also a good emitter, a perfect black body would be the ———– possible emitter.
best best
The amount of radiation emitted by a body (object) depends on its …
surface area and surface temperature.
Bodies with a large surface area will emit radiation …
faster.
Bodies with a ———- surface temperature will emit radiation faster.
higher
All bodies (objects) emit …
radiation.
A body at constant temperature absorbs radiation at the same rate that it …
emits radiation.
An object will always transmit (send) heat from a …
hotter area to a colder area.
An object will always transmit (send) heat from a hotter area to a colder area.
Radiators work based on this principle.
This means that when an object’s internal temperature is higher than the temperature of the environment around it, the rate of emission will be …
higher than if the object were in a warmer environment.
Black bodies are perfect absorbers and emitters of radiation - they never …
reflect or transmit radiation.
The rates of absorption and emission can be affected by:
- Surface area
- External temperature
- Internal temperature
The temperature of a body (object) depends on the rate of …
absorption of radiation and the rate of emission of radiation.
Objects get —— if they absorb more radiation than they emit.
hotter
What happens to a body which absorbs the same amount of radiation as it emits?
its temperature stays the same
The process behind the greenhouse effect is:
- The sun emits short wavelength infrared radiation that enters the atmosphere and travels towards the Earth’s surface.
- The Earth absorbs some of this radiation, but long wavelength radiation is reflected back into the atmosphere.
- Greenhouse gases (e.g. carbon dioxide, methane, water vapour) can’t absorb the frequency of radiation emitted by the Sun. But they can absorb the longer wavelength reflected radiation.
- The gases then re-radiate this energy in all directions, including back towards Earth.
- This increases the temperature at the Earth’s surface.
Greenhouse gases are unable to absorb the frequencies of radiation that arrive from the Sun. However, they do absorb some ——– radiation before re-radiating it in all directions, including back towards Earth.
reflected
There is a ——- between heat energy absorbed by the Earth and emitted by the Earth.
balance
Absorbed sunlight is balanced by …
heat radiated from Earth’s surface and atmosphere.
Most heat escapes from areas …
just north and south of the equator, where the surface is warm, but there are few clouds.
Along the equator, ——- prevent heat from escaping.
persistent clouds
—— Watts per square metre of solar energy falls on the Earth.
340
—— of solar heat is reflected back into space - primarily by clouds, but also by other bright surfaces and the atmosphere itself.
29%
29% is reflected back into space - primarily by …
clouds, but also by other bright surfaces and the atmosphere itself.
About —– of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles.
23%
About 23% of incoming energy is absorbed in the atmosphere by …
atmospheric gases, dust, and other particles.
About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles.
The remaining 48% is absorbed at the …
surface.
About 23% of incoming energy is absorbed in the atmosphere by atmospheric gases, dust, and other particles.
The remaining —- is absorbed at the surface.
48%
Why is it important to maintain satisfactory levels of greenhouse gases on earth?
Without greenhouse gases, temperatures would be too low to support life.
However, high concentrations of greenhouse gases cause the temperature to rise too high, which also threatens life on Earth.
What happens to energy from the Sun which hits the Earth:
- Absorbed by the Earth’s surface
- reflected by atmosphere
- absorbed by atmosphere
Which type of lens focuses light onto a principal focus?
convex
Heat radiation is transmitted via which form of wave?
infrared
What distinguishes one colour from another?
wavelength
