Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > M7 Nature of Light > Flashcards

M7 Nature of Light Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

James Clerk Maxwell (1831-1879) proposed

A
  • electricity and magnetism are spatially linked
  • light propagated as an electromagnetic wave
  • other wavelengths exist beyond visible spectrum
  • proposed speed of light is 1/sqrt(mu0 x epsilon0)
  • proposed light is electromagnetic radiation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Permeability of free space (mu0)

A

the constant of proportionality which gives the strength of a magnetic field due to a current in a vacuum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Permittivity of free space (epsilon0)

A
  • constant representing how fast an electric field can propagate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Spectrum

A

Long to short wavelength, low to high frequency (c = f). Radio waves, Microwaves, Infrared, Visible, Ultraviolet, X-rays, Gamma-rays (Randy May I Visit Ur X-Girlfriend).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Heinrich Hertz

A

Showed that electromagnetic waves travelled at the speed of light and could be polarised, reflected, refracted and diffracted, just like light. Used radio waves.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Production of Electromagnetic Waves

A
  • Gamma rays are produced by charges oscillating in the nucleus of atoms.
  • Visible light by charges oscillating in atoms. Infrared by charge oscillation in molecules.
  • Radio waves by charge oscillation in metal wires (antenna).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Scientists experiments for speed of light

A
  • Galileo 1638 - s=dt method (hills, water-clock, human reaction time).
  • Ole Romer 1676 - Jupiter’s moon Io (orbit times).
  • James Bradley 1728 - Stellar aberration.
  • Hippolyte Fizeau 1849 - Toothed Wheel.
    0 Leon Foucault 1862 - rotating mirror.
  • Maxwell 1864 - v=1/sqrt(mu0 x epsilon0) created formula which was then used by Rosa, Dorsey.
  • Albert Michelson 1879 - rotating 8-sided mirror.
  • Rosa and Dorsey 1907 - electromagnetic constants.
  • Louis Essen, Gordon-Smith 1947 - cavity resonator v=f.
  • Froome 1958 - radio interferometry 299 792.5 +/- 0.1 km/s.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Young’s Double Slit Experiment

A

dsin(theta) = m x lambda and x(m) = mLlambda / d. (sin(theta) = x(m)/L) (also equations for single slit diffraction).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Energy of a photon

A

E = hf. h is planck’s constant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Absorption

A

Absorbed radiation may also be re-radiated, sometimes as another form of EM radiation. Water strongly absorbs microwave radiation. The absorption of microwaves is a strong indicator of the presence of water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Blackbody

A

perfect emitter or absorber of electromagnetic radiation. E.g. black hole.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Continuous spectra

A

whole rainbow, no black lines, some colours can be brighter than others.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Blackbody radiation

A

In terms of visible EMR it is the whole spectrum but varying intensity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Excited electrons ground state

A
  • Balmer Series (visible) - 2nd energy shell.
  • Lyman Series (Ultraviolet) - 1st energy shell.
  • Paschen (Infrared) - 3rd energy shell.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Electron volts

A

the amount of kinetic energy of an electron when it is accelerated across an electric potential difference of one volt.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Voltage in terms of work

A

V = W/q work per charge (J/C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Refractive index

A

n = c/v c is the speed of light, v is the speed of light in the material.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Spectroscopy

A

study of how electromagnetic radiation interacts with matter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Determining star characteristics

A
  • Temperature - apparent colour, high to low: blue, white, yellow, orange, red, Wien’s displacement law lambda(max)= b / T.
  • Rotational, translational velocity - uses redshift caused by doppler effect, analysed by spectral lines, rotational: one side is redshifted, one side is blueshifted, therefore absorption lines are broader.
  • Density = In dense gases the particles are closer together and have a higher rate of atomic collisions, the absorption lines are broadened, called pressure/collisional broadening.
  • Chemical composition - absorption lines occur at specific wavelengths known to an element, intensity determines the amount of that element.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Diffraction around object/gap width (d)

A

Interrupted ends of wavefronts curl around a barrier because circular secondary wavelets at ends move outwards. If wavelength is way less than d, unnoticeable diffraction. If lambda < d noticeable diffraction. lambda approx = d most diffraction. If lambda > d mostly just reflected.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Newton’s Corpuscular (Particle) Theory

A
  • If light was a wave, it should display diffraction patterns that would obliterate all shadows, therefore particle theory. Light consists of small particles (corpuscles). These particles have mass (wrong) and obey the laws of physics. The particles are so small that, when two beams cross, they do not scatter each other.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Snell’s Law

A

sini/sinr = v1/v2 = lambda1/lambda2 = n2/n1 angles measured to the normal.

23
Q

Diffraction grating

A

lots of slits in a small area. Longer wavelengths have a greater diffraction angle.

24
Q

Application of diffraction

A

x-ray crystallography was used to determine the structure of DNA to be a double helix.

25
Q

Newton’s model of reflection of light

A

matched Snell’s law but got the speed of light in different mediums round the wrong way.

26
Q

Huygens’ model of light

A

Longitudinal wave (like sound). Propagated through a medium called an ‘aether’. Disproved by Michelson-Morley aether wind experiment.

27
Q

Huygen’s principle

A

point sources produce wavelets which creates a linear wavefront (rectilinear propagation).

28
Q

Malus’ Law

A

I = I(max)cos^2(theta) where I is the intensity of light passing through the filter in cd (candela). I(max) is the light intensity entering the filter. However, polarised light going through the first filter only leaves 0.5 of the intensity. Polariser is the first filter, analyser is the second.

29
Q

Simeon Poisson

A

Projected light onto a disk. Believed if wave theory was correct there would be a central bright spot. He didn’t observe this so thought the wave theory was disproved, however, others did observe it. The pattern came to be known as the ‘Poisson bright spot’.

30
Q

Polarisation

A

Polarisation of light occurs when the electrical field component of the electromagnetic wave is constrained to oscillate in one plane. The transmission axis of electrically conducting polarising discs is perpendicular to the long-chain hydrocarbon molecules. Parallel will get absorbed. Only transverse waves can be polarised.

31
Q

Photoelectric effect

A

Creating electricity from photons (solar panels). Particle theory. E = hf. Photons of threshold frequency (enough energy) liberate a photoelectron (electron) from a metal.

32
Q

Voltage (Ohm’s Law)

A

V = IR

33
Q

Thermionic emission

A

when photons liberate electrons from metals, excess energy goes into kinetic energy for the electron (leading to higher voltage). An increase in intensity (amount of photons) results in an increase in current.

34
Q

Kinetic energy

A

K(max) = photon energy - work function = hf - Φ. Work function is the energy required to liberate an election, also equal to hf, just a different f.

35
Q

Stopping voltage

A

the electric potential difference that just stops the electrons from reaching the right plate. Vstop = Kmax in eV.

36
Q

Frame of reference

A

where an observation is being made from.

37
Q

Galileo’s Principle of relativity

A

when in an inertial frame, you cannot tell if you are moving or not without looking outside your own frame of reference.

38
Q

Non-inertial frame of reference

A
  • one that is accelerating with respect to a reference frame.
  • Newton’s laws of physics are not always obeyed.
  • Distinguishable from inertial frame by hanging mass on train experiment.
39
Q

Inertial frame of reference

A

one that is at rest or moving with constant velocity. Twin paradox. Laws of physics are obeyed.

40
Q

Einstein’s Special Relativity Theory Postulates

A
  1. The laws of physics are equivalent or hold true in every inertial frame of reference.
  2. The speed of light is constant in all inertial frames. It is a universal constant, no matter how fast the source of light and observer are moving relatively.
41
Q

Mirror on a train thought experiment

A

train at speed of light. If he could see his reflection, then light must be able to travel at its normal speed relative to the train. Therefore, c must be constant and independent to the motion of the observer.

42
Q

Consequences of special relativity

A
  • Variable quantities (time, length, mass and momentum dilation)
  • new metre definition (used to be a 10 millionth of distance from equator to north pole, now is length travelled by light in 1/299 792 458ths of a second)
43
Q

Relativity of simultaneity

A

when two events occur at the same time in one reference frame, but different times for another. Thought experiment: man on the train, light in middle, 2 doors either end opening, observed on platform.

44
Q

Time Dilation

A

td = t0 / sqrt(1-v2/c2) lorentz factor is 1/square root bit.

  • Thought experiment: light clock on train travelling at relativistic speeds. Observer on platform sees diagonal ticks. Observer on train sees straight up and down.
  • Moving clocks in other frames of reference appear to tick slower.
  • Dilated time is always larger than proper time.
45
Q

Fish in elevator experiment

A

When elevator accelerates upward, mass of fish is greater and vice versa. Phenomenon of weightlessness.

46
Q

Length contraction

A

The faster you travel through space the shorter an object becomes in the direction of its motion (only one plane, not height or width). l = l0 x sqrt(1-v2/c2)

47
Q

Atomic Clocks - The Hafele-Keating Experiment

A

experimental proof for time dilation.

  1. Using very accurate atomic clocks. One on aircraft which flew at high speed for a long distance, other in an aeroplane. Clock on aircraft had slowed down.
  2. Caesium Atomic Clocks. Difference for planes heading east and west.
48
Q

Observations of Cosmic Muons at the Earth’s Surface

A

proof for time dilation and length contraction.
Muon (mu) is formed when high energy protons (from cosmic rays) collide with carbon or beryllium nuclei in the atmosphere (10km). However, they have been detected at the Earth’s surface. They have a lifetime of 2.2 x 106s so if time dilation didn’t occur, they should only travel 600m. However, survival rate is 0.3 per million. Scientists calculations of densities of muons on Earth based on half-lives are different to the measured densities. From muons frame of reference, length contracts in its direction of motion.

49
Q

Evidence from particle accelerators

A

Moving clock: accelerated lithium ions to 1/3c. Measured a set of transitions within the lithium as electrons jumped between energy levels. Transitions within lithium ions that were not moving represented the stationary clock. The time dilation found was what was expected, supporting theory of SR.

50
Q

Evidence from cosmology

A

black holes releasing relativistic jets of plasma. Time dilates, making these jets very stable and their frequency changes.

51
Q

Mass Dilation

A

m = m0 / sqrt(1-v2/c2)

As velocity increases, so does mass.

52
Q

Relativistic momentum

A

p = m0v / sqrt(1-v2/c2)

53
Q

Force of exhaust on rocket

A

a(rocket) = FR / mrocket x sqrt(1-v2/c2)

Physics (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions