Physics - Properties of Light Flashcards
Waves definition
Waves are motions which carry energy from one place to another
What are the two types of waves?
Transverse and Longitudinal waves
Transverse waves and examples
the vibrations are at right angles to the direction of travel
eg. X-rays, microwaves, radio waves, Seismic waves
Longitudinal waves and examples
the vibrations are in the same direction as the direction of travel
eg. Sound waves, spring waves, A vibrating drumhead
Can waves travel in all 3 dimensions?
Yes
1 dimension wave travelling example
A longitudinal or transverse wave travelling along a rope. The rope confines the energy to the rope
2 dimension wave travelling example
A transverse wave travelling from a point source of disturbance in still water – a pebble in a pond
3 dimension wave travelling example
Sound waves travel immediately away from the source in 3-dimentions with a spherical wave front. A source of light will illuminate a 3-dimentional space
The wave model - Initial level
The line that is positioned at roughly the middle of the crest and trough
The wave model - Amplitude
The space between the crest and the mean position (the middle line between the crest or trough)
The wave model - Crest
Where the displacement of the medium is at the maximum (when the movement of the medium from it’s initial position [which was before the wave travelled through it], was at the maximum)
The wave model - Trough
The lowest point from the mean position in a wavelength
The wave model - One wavelength
Trough to trough or crest to crest
Amplitude definition
The distance between the maximum height of displacement of the medium from its equilibrium position (the undisturbed state of the medium), and is usually measured in meters.
(For transverse waves the amplitude is half the distance between the crest and trough)
Wavelength in transverse waves vs longitudinal waves
Transverse waves - The wavelength is the distance between 2 continuous crests or two troughs
Longitudinal waves - The wavelength is the distance between two adjacent zones of compression or rarefaction
Rarefaction
When the frequency of the waves is low in longitudinal waves
Compression
When the frequency of the waves is high in longitudinal waves
Frequency (f) and the units used with it
The number of waves produced by a source or number of complete cycles (the up and down pattern) each second
The unit used if often Hertz (hz) per second however kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) can be used if the frequency is very high
Period (T)
The time in seconds for one complete cycle (the up and down pattern)
Equation for period (T)
T = 1/f
Equation for frequency (f)
F = 1/T
Phase
If two points on a wave are in phase, at a particular instant in time, they have the same displacement and same velocity
(Imagine drawing a set of waves and then another set of waves directly on top of it and on the same line [a line over a line})
Equation for velocity
V = change in displacement/change in time
V = (triangle) s / (triangle) t
Wave speed/velocity and what unit is used
Wave speed (metres per second) = Frequency (Hertz) x Wavelength (Metre/s)
V = f x λ
The answer is in metres per second (m/s)
What is the symbol ‘λ’ and what does it show
The symbol’s name is ‘lambda’ and it shows the wavelength of any wave
Difference between sound and light waves
Sound waves are mechanical waves meaning they need a medium to move
Light waves are electromagnetic waves and do not need a medium to travel which is how the sun and stars can reach us in Earth
Types of electromagnetic waves (from lowest frequency to highest frequency)
Radio waves
Micro waves
Infrared waves
Visible radiation (visible light)
Ultraviolet waves
X-rays
Gamma waves
Radio waves purpose/examples
Communication, Tv, phone, medicine
Micro waves purpose/examples
Type of radio waves used in cooking and cell phone communication
Infrared waves purpose/examples
Military, Police, Medicine, Heat detection
Visible Radiation (Visible light) purpose/examples
Allows the human perception of objects (allows us to see things and see them with colour)
Ultraviolet waves purpose/examples
Enables skin cells to produce vitamin D, kills bacteria, can cause skin and eye damage if exposed
X-Rays purpose/example
Medicine
Gamma Waves
Cancer treatment (killing the cells)
The more higher the frequency of a wave…
the more dangerous/strong it can be
What is radio waves good for?
Transmitting signals over long distances as they have the longest wavelength
What is the frequency of radio waves?
10^3 to 10^9 hertz
What does EMS stand for?
Electromagnetic Spectrum
What is AM and FM radio
When we turn on radio we turn on AM or FM radio
Microwaves are radio waves…
with the shortest wavelength
Why are Microwaves used in cell phone communication?
This is as they do not get easily blocked by trees, mountains, etc…
What type of objects give of Infrared radiation?
Any hot objects
What is visible light made up of?
The colours of the rainbow is how we see them
Gamma rays have the most … and the highest …
Energy
Frequency
In what shape does light travel? (Bent line, straight line, curved line, etc…)
Straight line
How do we see objects that don’t even emit light?
The light is reflected
What kind of wave is a surface ocean wave? (transverse or longitudinal)
Waves on the surface of the ocean are transverse waves since the water is moving up and down and therefore at 90° to the direction the wave travels
Opaque
Does not allow light to pass through
All light is either absorbed or reflected
Translucent
Can be seen through, but not clearly
Allows some light to go through, but some is also absorbed or reflected
Transparent
Allows almost all light to go through, so can be seen through clearly
What colour is made up of all the colours of the rainbow?
White
White light
Reflects all light and absorbs none
Black light
Absorbs all light and reflects none
Three secondary colours of light
red + blue = magenta
blue + green = cyan
red + green = yellow
and the equations
Three primary colours of light
green
red
blue
What type of waves are light waves? (transverse or longitudinal)
Transverse
Absorption
The transfer of light energy into an object where it is transferred into heat energy (the object gets hotter)
Transmission
When light passes through an object without being absorbed or reflected
Normal
The “normal” is a line perpendicular (at 90° degrees) to a surface
Incident ray
The ray of light before it reaches a surface
Reflected ray
The ray of light that has reflected and bounced of off a surface
Angle of incidence
The angle between incident ray and normal line
Angle of reflection
The angle between reflected ray and normal line
Law of reflection
If the ray is reflected on a smooth surface then the angle of incidence and the angle of reflection will be the same degrees
Diffuse reflection
When light (a light ray) is reflected off of a uneven or rough surface and is reflected in different directions
Pulse
A singular wavelength or less (maybe half a wavelength [only the up or down curve])
Periodic/Continuous waves
Waves that keep on going in a pattern constantly
Photon
A particle of light
Reflection
When light rays are bounced off of an object as a reflected ray
No light is absorbed or transmitted
Where is the normal located
At 90 degrees to the contact point
If at flat surface then normal would be a straight line in the middle however if on a rough/angled surface then it would be a straight line on an angle exactly where contact was made
Refraction
When a light ray hits a surface, it will change speed and direction
For example, a straw in a bottle
Does colour change in a light ray when a light ray goes through an object?
No
Medium boundary
A surface
Critical angle
the angle above which total internal reflection occurs
When a light ray hits water from air, it turns/reflects 90 degrees
Media
Multiple mediums
Refractive index (n)
A ratio of speed of light in a vacuum compared to light in that medium (in simple words it describes how much a light ray changes/bends from one medium to another
Vacuum
A place where matter does not exist and there is no medium
For example, space does not stop light and has not matter/media
Total internal reflection
The reflection of all incident light at a boundary between two media
Refractive index equation
n = c/v
c = speed of light in a vacuum which is 300,000,000 m/s (3 times 10^8)
v = speed of light in the medium
n = refractive index
IF NEEDED TO FIND V THEN REARRANGE THE EQUATION TO MAKE V THE SUBJECT
Speed of light in a vacuum
3 x 10^8 (300,000,000) m/s
You SUBSTITUTE this into the refractive index equation (n= c/v)
What happens to light if the medium is dense
The more dense a medium is the more the light bends towards the normal
Symbols for angle of incidence and reflection
Incidence = Qi (the I goes on the bottom)
Reflection = Qr (the r goes on the bottom)
Snell’s Law (all letters are on the bottom of the symbol next to it)
Ni Sin (theita i) = Nr Sin (theita r)
The angles of incidence and reflection go in the brackets, and the refractive index (n) goes outside. This law REQUIRES A CALCULATOR
You need inverse operations for this
This equation can be used to find the refractive index of the incidence and reflected ray
The bigger the ‘n’ value (refractive index) the….
slower light travels
How to determine when n is smaller or larger in refraction
If going from a less dense medium (ni is smaller) to a more dense medium (ni is larger) the ray will bend towards the normal. If the ray is bending away from the medium then it is the opposite (ni is larger then nr)
Does the frequency of a wavelength ever change when going medium to medium?
No why would it change u bum
When should numbers be rounded when calculating
You can round numbers when writing them mid equation so you don’t have to write it all but you must not round it in your calculations
What does Sin give us?
The sin gives us the opposite side over the hypotenuse
You would put ‘sin(whatever the angle is to the side of the right angle)’. This would give
What does sin-1 give us?
We use this when we know the opposite side and the hypotenuse yet we need to know the angle next to the right angle (the feitha angle)
We do ‘sin(opposite over hypotenuse)’
What happens when a critical angle occurs? Does the angle still refract?
A critical angle occurs from a dense medium to a less dense medium. The refracted ray bends exactly on the surface (90 degrees). The refracted index instead reflects off of the surface and applies the law of reflection. The refractive angle becomes the reflection angle.
Refractive angle
The angle that forms after the incident ray refracts
Total internal reflection
When the refractive ray is at 90 degrees and reflects
(It is why we can see reflections in water, however the bigger the angle the better it reflects, which is why when we look down in water form height there is less of a reflection as the angle is smaller but when we look further away in the water, there is more of a reflection as there is a larger angle)
Refractive ray
When the incident ray bends in a medium
If the incident angle is larger than the critical angle, can light bounce in curvy objects
What is the equation to find the critical angle
Theita c = Sin -1 (nr/ni)
the nr and ni is the refractive index of the refractive and incident mediums (media)
When do you use Snell’s law?
When it is a refractive angle question
What is the refractive index in air
1
What is the refractive index in water
1.33
Apparent depht
When looking into water for example, if u see a fish it looks shallower and further away than it actually is, however because of the refraction the light bends (refraction) and the fish is actually deeper in the water and closer to you. The fish is at the end of the refractive ray, however it looks differently
What happens if a light ray goes through a medium with a less refractive index compared to more?
If a light ray goes through a medium with a less refractive index, it moves away from the normal
If a light ray goes through a medium with a bigger refractive index, it move towards the normal
The bigger ‘n’ is in the refractive index equation, the ……… and the smaller ‘n’ is the ………..
The bigger ‘n’ is in the refractive index equation, the smaller the speed of light is
The smaller ‘n’ is the faster the speed of light is
Dispersion
Splitting of light into it’s various colours
What colour bends more when changing medium?
A blue light bends more when changing medium
What colour bends less when changing medium?
Red bends less when changing medium
(meaning the ray will be more like the incident ray before it hit another medium as it won’t bend much)
Scientific term for Rainbow
Full spectrum
What are the prime colours when mixing light?
Red, green and blue
Why do certain colours bend differently in light?
This is as different colours have a different refractive index (n)
What do you get from combining all three primary light colours
White light
Speed equation
d/t
What is special about mechanical waves?
They require a medium to pass through eg. sound waves
Wavelength equation (lambda)
Wavelength (lambda) = wave speed/velocity (v)/frequency (f)
