Light Flashcards
where does light originate from?
the accelerated motion of electrons
how do you generate waves of electric and magnetic fields (electromagnetic waves)
And why?
when you shake a electrically charged rod back and forth in empty space
- because the moving charge is an electric current and it is surrounded by a magnetic field
the electric and magnetic fields of an electromagnetic waves are ____ to each other
and are what type of wave?
perpendicular
transverse wave
There is how many speeds for which the electric and magnetic fields remain in perfect balance, reinforcing each other as they carry energy through space
one speed
an electromagnetic wave travelling through space ______ (what about speed) and what is it due to?
it never changes speed
due to the law of conservation of energy
If light were to slow down what would happen
its changing electric field would create a weaker magnetic field which creates a weaker electric field and energy would be lost
if light were to speed up what would happen
its changing electric field would create a stronger magnetic field which creates a stronger electric field and energy would be increasing
Maxwell calculated the value of the speed of light to be what?
300 000 km/s
Maxwell discovered that light is simply what type of radiation between what frequency ranges
electromagnetic radiation
4.3 X 10^14 to 7 X 10 ^ 14
Maxwell proved that light of any kind is…
energy - carrying waves of electric and magnetic fields that continually regenerate each other and travel at single fixed speed
The classification of electromagnetic wavees acccording to frequency is the
electromagnetic spectrum
List the electromagnetic spectrum from longest to shortest wavelength
radio waves, mircrowaves, infrared light, visable light, ultraviolet light, xrays, gamma rays
List the electromagnetic spectrum from highest frequency
gamma rays, xrays, ultraviolet light, visable light, infrared light, microwaves, radio waves
the ___ the frequency of the vibrating charge, the _____ the wavelength of radiation
higher
shorter
visable light makes up less than a ______ of the measured electromagnetic spectrum
a millionth of 1%
what is the lowest frequency light that we can see with our eyes (colour)
red
the highest frequencies of visable light are nearly twice the frequency of red and appear
violet
what type of boundries are there between the regions
not sharp, they overlap
when a light wave with a single frequency strikes an object what 3 things can happen
- reflected by the object
- transmitted by the object
- absorbed by the object in which case its energy is converted to heat
The way a material responds depends on
the frequency of the light and the natural frequency of the electrons in the reieving material
Absorbtion occours when
the frequencies of the light waves is the same as the natural frequencies of vibration of the objects. these electrons will absorb the energy of the light wave
Reflection and transmission occour when
the frequencies of the light waves do not match the natural frequencies of vibration of the objects. the electrons vibrate for brief periods of time with small amplitutes; then the energy is transmitted as a light wave
If the object is transparent then..
the vibtrations of the elctrons are passed on to neighbouring atoms through the bulk of the material and reemitted on the opposite side of the object. such frequencies of the light waves are said to be transmitted
If the object is opaque…
the vibtrations of the elctrons are not passed on to neighbouring atoms through the bulk of the material. rather the electrons of the atoms on the material’s surface vibrate for short periods of time and then reemit the energy as a reflected light wave. such frequencies of the light waves are said to be reflected
what is reflection
when light is returned into the medium from which it came
what is refraction
when light crosses from one transparent material into another
usually some form of what occurs when light interacts with matter
reflection,refraction,absorption
when there is nothing to obstruct its path light travels in
a straight line
What does the path of light always follow?
Fermat’s Prinicple of Least Time
Fermat’s Prinicple of Least Time
out of all possible paths that light might take to get from one point to another it takes the path that requires the shortest time
Following the principle of least time the least time path will be the
shortest path - if the speed doesnt change
The Law of Reflection states that
the angle of reflection is equal to the angle of incidence
When light is incident on a rough surface …..
it is reflected in many directions and is called a diffuse reflected
a flat mirror is called
a plane mirror
a virtual image is formed where and when
formed behind the mirror and is located at the position where the extended reflected rays converge
Image Characteristics
- Type
- Attitude
- Magnification
- Position
- real or virtual
- upright or inverted
- same size, smaller, larger
- distance from mirror surface
What are virtual images
image formed by rays that do not converge at the location of the image
what are real images
Image formed by rays that converge at the location of the image
When the mirror is curved, the sizes and distances of object and image are
no longer equal
Convex mirror
- curves outward
- virtual image formed is smaller and closer to the mirror than the object.
Concave Mirror
- curves inward
- virtual image is larger and farther away than the object
Does light travel at different speeds in different materials
yes
light travels how fast in a vacuum
300 000 km/s (c)
does light travel faster or slower speed in air
slightly slower speed
how fast does light travel in water comparative to vacuum
3/4ths
Index of refraction
how much the speed of light differs from its speed in a vacuum
- never less than one
- shown by the equation
n = speed of light in a vauccum (c)
———————————————
speed of light in a material
n = c/v
Whether reflection or refraction, the path of light follows
fermat’s principle of least time
When does refraction occour
when the average speed of light changes in going from one medium to another.
when light travels from less dense to more dense medium it
slows and bends towards the normal
when light travels from more dense to less dense medium it
speeds up and bends away the normal
if the angle is large enough then the angle of
refraction will be
parallel to the medium boundry
what is the critical angle
the minimum angle of incidence at which a light ray is totally reflected
If the incident angle is greater than the critical angle what happens and what is it called?
all light is reflected
Total Internal reflection
What is total internal reflection
If the incident angle is greater than the critical angle and all light is reflected
critical angle - angle of incidence when angle of reflection = 90
Snell’s law
- quantitative law of refraction
diverging lens
thinner in the middle
converging lens
thicker in the middle
roundish
when is an image real?
when the light rays actually converge and pass through the image
- real image can be seen on a piece of paper or a screen
when does a virtual image happen?
when the image is formed in locations where the light noes not converge
- always located behind the mirror
concave mirror
converging curves in (backwards c)
convex mirror
diverging curves outwards (c)
concave lens
diverging
thinner in middle
convex lens
converging
roundish - fat in middle
if it is converging and the object is at the focal point what happens
no image
