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The Nature of Light Flashcards

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1
Q

Who Proposed that light was a form of Electromagnetic radiation (EMR)

A

Maxwell

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2
Q

How does the Electromagnetc wave work

A

He proposed that if a changing elecric field is produced, it will also produce a magnetic field at right angles to the electric field. The changing magnetic field would then in turn produce a changing electric field and the cycle be repeated. In effect this would produce two mutually propagating fields oscillating at the same frequency.

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3
Q

what is the formula for the speed of light

A

c = f x h

c is the speed of light (ms^-1)

f is the frequency of the wave (HZ)

h is the wavelength of the wave (m)

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4
Q

How did Heinrich Hertz support Maxwell’s theory

A

in the 1880s Heinrich Hertzs performed experiments that demonstrated the existence of ‘invisible’ electromgantetic waves (radiow waves).

His basic experiment design involved a high voltage source to produce a spark and a detector formed from a loop of a copper wire with a small gap. Radio waves produced by the spark were detected when a tiny spark was induced across the gap in the detector. He found that the invisible waves behind like visibile light, and the speed of the waves was the same as the speed of the light.

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5
Q

How siginificant were Maxwell’s theory of light was

A

He provided an explantation of the nature of light, but also a strong theoretical basis for the wave model of light as he brought together several formerly distinct areas of study to form his theory

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6
Q

how did Hippolyte Fizeau experiment calculate the speed of light

A

Fizeau shone a bright light through a toothed cogwheel. As the wheel turned, sometimes light would be blocked by the cogs. Fizeau set up a mirror 8km away from the cog in order to measure the time-of-flight for light to travel the 16km path. As the pulse of the light needed to pass again through the teeth on the way back for it to be observered, knowing the speed of the rotation of the wheel, and knowing the distance between the cogwheel and the mirror, Fizeau was able to calculate the speed of light to be approximately 315 000kms^-1

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7
Q

how did Leon Foucault calulate the speed of light

A

Leon Foucalt refined Fizeau’s method by using a rotating mirror to block the light’s path and by 1862 he deteremined a result of 298 000 kms^-1 which is just over the 0.5% off the modern estimate.

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8
Q

What is the electromagnetic spectrum

A

the range of all types of radiation that has both electric and magnetic fields that travel in waves.

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9
Q

what are the different waves in the electromagnetic spectrum

A

AM radio wave: 100m wavelenght and 3 x 10^ 6 Hz frequency

FM radio or TV wave: 3m wavelength and 1 x 10^8 Hz frequency

Microwaves: 0.03 m wavelength and 1 x 10^10 Hz frequency

infared: 10^-5m wavelength and 3 x 10^13 Hz frequency

Visible light: 10^-7m wavelength and 3 x 10^15 Hz frequency

Ultraviolet: 10^-8m wavelength and 3 x 10^16 Hz frequency

X-ray: 10^-10m wavelength and 3 x 10^18

Gamma ray: 10^-15 m wavelength and 3 x 10^23

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10
Q

what type of waves are Electromagnetic waves

A

Transverse waves

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11
Q

What is spectroscopy

A

The brance of science investigating the spectra produced when matter interacts with or emits electromagnetic radiation is reffered to as spectroscopy.

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12
Q

What is spectroscopy used for

A

it is widely used in chemistry to detect and characterise atoms and molecules, as well as in astronomy and sensing technologies.

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13
Q

What are the types of spectra

A

Absorption

Emission

Black body radiation/continuous spectra

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14
Q

What is the absorption spectra

A

It is where light passing through an object has dark/missing lines from the spectrum. The dark/missing lines represent absorbed wavelengths or frequencies by certain elements of the object. By comparing the absorbed lines to elements, scientist can determine which elements are present in the object.

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15
Q

What is Emmision Spectra

A

When elements are heated to high temperature, or have an electrical current passed through them, they produce light. The Atoms in the material absorb energy and become ‘excited’ which makes the atom unstable and eventual return to the ‘unexcited’/ground state. The colour of light that becomes excited are the missing/darklines from the Absorption Spectra.

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16
Q

where is the visible spectrum around in wavelength

A

400nm and 750nm

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17
Q

What is an Incandescent light bulb

A

it is a lightbulb that produces light by heating a metal filament to a very high temperature, this produces electromagnetic radiation at a range of wavelengths; that is, the light from the incandescent globe is a continuous spectrum.

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18
Q

What are Discharge tubes

A

Discharge tube contains low-pressure gas through which a current is passed. The light emitted by the gas is in the ultraviolet range. The inside of the glass is coated with a material called a phospher, the ultraviolet light excites the phoser which then emits light over the entire visible spectrum. They emit less energy in the infrared range so more effciently convert the electrical energy into light energy and remain cool to touch, however they are much more expensive to manufacture incandescent globe but it has much lower running costs. Fluroesecnt lights are a type of discharge tube.

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19
Q

Do Planets and moons emit light?

A

no, they reflect light from a nearby luminous body like a star.

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20
Q

How can we determine what elements are in a star

A

by matching the missing bands in the absorbption spectra to the absobring substance.

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21
Q

What are the types of astronomies

A

Radio astronomy studies emission from cold objects such as interstellar gas and the cosmic microwave backgroudn radiation residual from the big bang

Submillimetre astronomy is used to look at molecular clouds and galaxy formation

infared astronomy is used to study star clusters, proto-stars and planets

Optical(visible) astronomy is the oldest form and reveals the chemical composition and temperature of stars.

Ultraviolet astronomy is used to study hotter objects such as young stars or stars approaching nova

X-ray astronomy studies very hot objects at temperatures of millions of degrees

Gamma-ray astronomy studies nuclear processes like supernova explosions and matter-antimatter interaction

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22
Q

what is the formula for Wien’s law

A

h = b/T

h is the peak wavelength (m)

T is the temperature in kelvins (K)

b is the Wien’s constant (mK)

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23
Q

Is the peakwavelength of an emitted light inversely proportional to the temperature of the object

A

yes

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24
Q

What is Redshifting

A

it is when the absorbption lines in the spectra are slightly longer (moved to the right) and it indicates that the planet/object is moving away from

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25
What is Blueshifting
Similar to Redshifting it is instead when the absorbption lines int the spectra are shorter and it indicates that the planet/object is moving towards us (approaching).
26
how can we determine the rotation of the star
We can determine if the planet/object is rotating quickly if the absorbption line is Thick, but it is rotating slowly when the absoprtion line is Thin.
27
How can we determine the density of a planet
by observing the brightness and temperature of the star.
28
Who proposed that Light was a Wavel
Christian Huygens
29
What is Huygen's Principle
Huygens' principle states that each point on a wavefront can be considered a source of secondary wavelets (small waves).
30
what are properties of Light that can only be explained by the Wavemodel
Diffraction Interference Polarisation
31
What is diffraction
when a plane (straight) wave passes through a narrow opening, it bends. Waves will also bend as they travel around obstacles. This kind 'bending' is known as diffraction.
32
how to convert nanometer to a meter
1nm is equal to 1 x 10^-9 meters
33
what is interference
it is when two or more waves interact with eachother to form a resultant wave of greater, lower or the same amplitude
34
when the light waves are made to shine on a screen which areas are constructive interference and which are destructive interference
Constructive interference will appear as bright bands, where as destructive interference will appear as dark bands.
35
How can you change a diffraction
If the wavelength is held constant and the gap is made smaller, a greater diffraction is seen If different wavelengths enter the same gap, those with a smaller wavelength will undergo less diffraction then those with a longer wavelength (red wavelengths are long, blue wavelengths are short) the amount of closely spaced gaps or slits.
35
Who's experiment support Huygen's wave model theory
Thomas Young's Double slit exepriment
36
What was Young's Double Slit experiment
Young shone a monochromatic light on a screen containing tow very tiny slits. on the far side of the double slits he placed another screen in which he observed a pattern produced by the light passing through the slits. Young observed a series of bright and dark bands of 'finges' which according to the particle theory should not have happened, and should've only produced two bright lights on the screen
37
what is the path difference
the path difference is the difference in the distance travelled by each wave train to a point P on the screen
38
what is the formula for the path difference
pd = |S1P - S2P| pd is path difference S1 is wave source one at point p S2 is wave source two at point p
39
when does constructive interference of coherent waves occur
when the path difference is equal to a whole number of wavelengths where pd = m x h where m = 0, 1, 2, 3...
40
when does destructive interference of coherent waves occur
when the path differenct is equal to an odd number of half wavelengths where pd = (m-1/2)wavelength, where m = 1, 2, 3....
41
what is the formula for calculating the fringe separation
d sin(angle) = m x h d is the slit separation (m) (angle) is the position to a bright point on the screen (as an angle from the perpendicular bisector between the slits) m is any whole number, i.e. 0, 1, 2, 3.... h is the wavelength of the light waves(m)
42
what is polarisation
Polarisation occurs when a transverse wave is allowed to vibrate in only one direction. Example only vertical waves can past through a vertically oriented polarising filters where the horizontal waves will be blocked out from. When a wave passes through a polarised filter, the wave has a reduced amplitude.
43
what is Malus' law
the intensity of light is reduced as the light passes through a polarising filter; the amount of reduction depends on the relative orientation of the filter and the plant of light.
44
what is the equation for Malus' law
I = Imax cos^2 (angle) I is the intensity of light passing through the filter (cd) Imax is the intensity of light entering the filter (cd) (angle) is the angle between the direction of polarisation of the light entering the filter (angle0), and the axis of polarisation of the fileter (angle1)
45
What is Wien's law
It is the law that descibe the properties of heat radiation. Wien discovered that the peak wavelength at which an object will emit the maximum intensity of radiation is dependent on its surface temperature. It is also known as Wien's Displacement law
46
what is the formula for Wien's law
h(max) = b/t h(max) is the peak wavelength of the emitted radiation(m) b is Wien's constant (2.898 x 10 ^-3 mK) T is the surface temperature of the object (K (kelvins))
47
how to convert between kelvins and celcius
C = K - 273.15 C is celcius K is kelvins -273.15 (celcius) is the absolute zero (the lowest energy)
48
what is a black body
it is a theoretical object that completely absorbs all the rays of electromganetic radiation that fall on it regardlgess of the wavelength of the radiation. In other words it means that a black body does not reflect any radiation.
49
what are the three ways radiation can interact with matter
Reflected Transmitted Absorbed
50
What is planck's equation
Planck proposed a solution to solve problems about the properties of light that could not be explanined by the wave model, by assuming that light was emitted as discrete packets. These discrete packets of energy 'quanta', and developed an equation for the energy, E, of each quantum
51
what is the formula for Planck's equation
E = h x f E is the energy of a quantum of light (J) f is the frequency of the electromagnetic radiation (Hz) h is Planck's constant (6.626 x 10^-34 Js) or E = hc/h(wavelength) h(wavelength) is the wavelength in meters (m) c is the speed of light
52
how to convert an electron volt into joules
1 ev = 1.602 x 10^-19 J
53
what are photoelectrons
photoelectrons are electrons that were ejected from the surface of the metal due to light or other forms of electromagnetic radiation. This phenomenon is known as the photoelectric effect.
54
What is a photocurrent
It is the flow of electrons that flows through a material due to the photoelectric effect.
55
What is the threshold frequency
It is the minimum frequency of light which causes the electrons to be emmited from a metal surface to create the photo electric effecct.
56
what are the properties of the photoelectric effect
when the light intesntiy increases so does the photocurrent when the applied voltage is positive, the photoelectrons are attracted to the collector electrode (anode) when the applied volatage is negative, the photoelectrons are attracted back towards the illluminated cathode and are repelled by the collector electrode and the photo current is reduced.
57
what is the stopping voltage
It is a voltage for which no photoelectrons reach the collector. The stopping voltage is a constant for a particular frequency of light on a particular metal.
58
What is the work function
It is the amount of energy required to eject a photoelectron is a constant value that depends on the strength of the bonding within the metal.
59
what is the formula for the work function
(work function) = h x f h is Planck's constant f is the freshold frequency for that metal (Hz)
60
what is the formula for the maximum kinetic energy
K = hf - (work function) k is the maximum kinetic enegery of an emmited photoelectron (J or eV) workfunction (J or eV) h is Planck's constant f is the frequency of the incident photon
61
Who developed the quantum model of light
Planck and Einstein
62
what is a frame of reference
it describes where an observation is being made from.
63
what is an inertial frame of reference
it is a frame where Newton's laws hold true.
64
What is aether
it is the name of the the medium that physicst believed light travelled through before it was discovered that space was a vaccume.
65
what is the Michelson-Morley experiment
Experiment: Michelson attempted to measure the speed of light that travelled through the aether. He set up a device known as the interferometer to detech changes in the speed of light by measuring the samll difference in the time taken for the light to travel in two mutually perpendicular directions. appratus: They had a laser that fired onto a half-transparent mirror that was rotated so the light can reflect onto both the movable mirror and the screen. results: However he discovered that there was no difference, and unintentionally led to belief that the speed of light was a constant and the aether did not exist.
66
what is a postulate
to claim or assume the existence or truth of something. Especially when it is the basis for a reasoning or an argument.
67
What were Einstein's two postulates
1): The laws of physics have the same form in all intertial frames of reference. 2): Light travels through an empty space with a constant speed.
68
What are Netwon's two fundamental assumptions
Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external. Absolute space, in its own nature, without relation to anything external, remains always similar and immovable.
69
What was the consequence of Einstein's postulates
That Newton's fundamental assumptions of space and time being a constant is not valid.
70
What was Einstein's thought experiment about special relativity (train experiment)
The thought experiment invovled a train moving at a constant velocity. The train has a flashing lightbulb in the centre of the carriage. There a three observers, two inside the train and one outside the train. The observers inside observe the flashes of light as they reach the front and back walls of the carrigae to find that the flashes reach the front and back walls reach at the same time. The outside measures the same flashes of light. Because Eintstein states that light travels at a constant, the outside observer will measure that the light will reach the back wall first, because the wall is moving towards the light whereas the front wall is moving away.
71
How did Einstien explain the consequence of his experiment
He explains this by combining the three dimensions of space and the dimension of time to make space time.
72
What is the formula for Time dilation
t = to/ sqrt(1- v^2/c^2) to is the time observed in the moving frame (proper time) (s) t is the time in the stationary frame (s) v is the speed of the moving frame of reference (ms^-1) c is the speed of light (ms^-1) t should be > the to
73
What is the Hafele-Keating experiment
It was an experiment by Hafele and Keating to test Einstein's theory of relativity more specifically time dilation. They used four caesium-beam atomic clocks and placed two of them in aeroplanes to fly around the world. They compared the times from these clocks to two clocks that remained in a lab. The Aeroplanes first flew in the same direction as the rotation of the earth (east) and then the opposite direction (west). It was predicted that the clocks that flew to the east would lose time whereas the clocks that flew west would gain time, which eneded up being the results of the trip and therefore matched their prediction within 10% and experimentally confirmed time dilation.
74
What was the Twin paradox thought experiment
Einstein had two twins, one stayed on Earth while the other heads off on a long space journey. The travelling twin returns to find the remaining twin to be much older than he is. This is because on has been in an inertial frame of reference while the other has not because of experiencing acceleration.
75
What is the muon experiment
It was an experiment that proved time dilation. Muons have a mean lifetime of 2.2us and the time flight between the top and bottom of the mountain at nearly the speed of light was about 7 us. It was expected that there should be no muons detected on earth however the muons that were created by the comsic radiation were detected. This meant that the muons existed for a much longer period of time than they were expected to.
76
what is the formula for relativistic momentum
pv = (mo x v)/sqrt(1- v^2/c^2) mo is the mass measured at rest (in the stationary frame of reference) (kg) pv is the relativistic momentum in the moving frame (measured by an observer) (kgms^-1) v is the velocity (ms^-1) c is the speed of light (ms^-1) pv should always be greater than > the original momentum (mo x v) = po
77
What is the formula for length contraction
l = lo x sqrt( 1- v^2/c^2) l is the contracted length/ the length in the moving frame measured by an observer (m) lo is the proper length (the length measured at rest in the stationary frame of reference). (m) The contracted length is always < than the proper length. v is the velocity (ms^-1) c is the speed of light (ms^-1)
78
What is the Einstein's famous energy, speed and mass equation
E = mc^2 E is the total energy (J) c is the speed of light (ms^--1) m is the mass in kilograms
79
what is nuclear fusion
Nuclear fusion occurs when two light nuclei are combined to form a larger nucleus
80
what is the mass defect
It is the energy created from missing mass in a fusion or fission.

Physics (4 decks)

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