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Our Own Learning Stuff > Physics Stuff > Flashcards

Physics Stuff Flashcards

1
Q

Newtons first law?

A

An object in motion stays in motion, or an object at rest stays at rest, unless acted on by an external force

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2
Q

Newtons second law?

A

Force is directly proportional to change in momentum/time

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3
Q

Newtons third law?

A

If object a exerts a force on object b, object b exerts the sane force on object a

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4
Q

What is snell’s law

A

N1 sin(theta2) = n2 sin(theta2)

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5
Q

What is the area under a force time graph?

A

Impulse or change in momentum

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6
Q

What is the difference between an elastic and inelastic collision?

A

Kinetic energy is conserved in an elastic collision

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7
Q

How do you get percentage uncertainty of c if c = a b

A

Work out the percentage uncertainty of a and b and add them

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8
Q

How do you work out the percentage uncertainty of b if b = a^3 x c

A

Work out the percentage uncertainty of c and add it to 3x the percentage uncertainty of a

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9
Q

What is Kirchhoff’s 1st law?

A

Current flowing into a node is equal to the current flowing out of it

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10
Q

What is Kirchhoff’s 2nd law?

A

Sum of EMF = sum of voltage out

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11
Q

What is Coulomb’s law?

A

Two point charges exert a force on each other that is proportional to the product of the charges, and inversely proportional to the square of the distance

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12
Q

What is Faraday’s law?

A

Magnetically induced EMF is proportional to the rate of change of magnetic flux linkage

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13
Q

What is Lenz’s law?

A

The direction of the induced current is always such to oppose the change producing it (gives the -1 proportionality constant in Faraday’s law equation)

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14
Q

What is Kepler’s 1st law?

A

Planets move in elipses with the star at their focus

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15
Q

What is Kepler’s 2nd law?

A

Providing the time period between two sets of two points in a planet’s orbit is the same, the areas between star and each pair of planets is the same

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16
Q

What is Kepler’s 3rd law?

A

T^2 is proportional to r^3

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17
Q

What does an isotropic universe mean?

A

The universe looks the same no matter which direction you look

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18
Q

What does a homogenous universe mean?

A

Matter is distributed uniformly throughout the universe

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19
Q

What is accuracy?

A

Getting results close to the true value

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20
Q

What is precision?

A

Getting results that are close to each other

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21
Q

What is the initial stage of the universe?

A

The universe is a singularity, it is infinitely dense and hot

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22
Q

What is the first stage of expansion of the universe and when does it happen?

A

10^-35 seconds, inflation begins (the universe expands rapidly), the universe is full of high energy gamma photons

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23
Q

What is the second stage of expansion of the universe and when does it happen?

A

10^-6 seconds, the first fundamental particles form such as quarks and leptons

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24
Q

What is the third stage of expansion of the universe and when does it happen?

A

10^-3 seconds, quarks combine to form hadrons, most mass is created through pair production (gamma rays forming particle-antiparticle pairs).

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25
Q

What is the fourth stage of expansion of the universe and when does it happen?

A

100 seconds, protons and neutrons fuse to dorm deuterium and helium nuclei. Expansion is so rapid that no heavier elements are made.

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26
Q

What is the fifth stage of expansion of the universe and when does it happen?

A

380,000 years, the universe cool enough for full atoms to form as nuclei capture electrons. As a result, CMB radiation is formed.

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27
Q

What is simple scattering of X rays and at what energy does it occur?

A

The X ray interacts with the atoms and is scattered with no change in energy, up to 20keV

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28
Q

What is the photoelectric effect with regards to X ray scattering and at what energy does it occur?

A

The absorption of an X ray by an electron, which is then emitted, <100keV

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29
Q

What is Compton scattering of X rays and at what energy does it occur?

A

When an X ray removes an electron from an atom and is then scattered with reduced energy, between 0.5 and 5 meV

30
Q

What is pair production of X rays and at what energy does it occur?

A

When an X ray photon interacts with a nucleus, disappearing in place of an electron and a positron, greater than 1.02 meV

31
Q

Define the electric potential of a point in space?

A

The work done per unit charge bringing a positive charge from infinity to the point

32
Q

What is hubble’s law?

A

Speed of recession of a galaxy is proportional to distance from earth

33
Q

What is the definition of a parsec?

A

The distance from a base length of 1AU that subtends an angle of 1 arc second

34
Q

What are the three main components of the gamma camera and what do they do?

A
  • Collimator
    Only allows gamma photons travelling parallel to the axis to pass through
  • Scintillator
    Gamma photons are turned into light photons
  • Photomultiplier tubes
    Light photons are converted into many electrons to be received by the computer
35
Q

What is the limit for a star turning into a red giant Vs a red supergiant?

A

10 Solar Masses

36
Q

What is the Chandrasekhar limit?

A

1.44 solar masses, the point at which the electron degeneracy pressure is not great enough to prevent a star’s core from collapsing into a neutron star

37
Q

What is the limit for a star’s core forming a black hole?

A

3 Solar Masses

38
Q

What is the limit of proportionality of a material?

A

The point at which the material stops obeying Hooke’s law

39
Q

What is the elastic limit of a material?

A

The point at which a material begins to deform plastically

40
Q

What are yield points of a material?

A

The turning points in a stress/strain graph, where the material extends rapidly

41
Q

What is the ultimate tensile strength of a material?

A

The highest tensile stress a material can withstand before breaking, characterised by the highest point on a stress/strain graph

42
Q

What is the breaking strength of a material?

A

The stress value at the point of fracture, characterised by the end of a stress/strain graph

43
Q

What is the definition and the two requirements of simple harmonic motion?

A

Oscillating motion for which the acceleration is given by:
a = -ω^2 x
Where:
- Acceleration is directly proportional to displacement
- The acceleration is in the opposite direction to the displacement

44
Q

What is an isochronus oscillator?

A

An oscillator in simple harmonic motion where the amplitude is independent of the time period

45
Q

What scale is the nucleus of an atom on?

A

10^-14

46
Q

What is Boyle’s law?

A

Pressure ∝ 1/Volume

47
Q

What is Gay-Lussac’s law?

A

Pressure ∝ Temperature

48
Q

What is Charles law?

A

Volume ∝ Temperature

49
Q

What is Avagadro’s law?

A

Volume ∝ Moles

50
Q

What is drag proportional to?

A

V^2 and area

51
Q

At what range is the strong nuclear force attractive?

A

Up to 3fm

52
Q

At what range is the strong nuclear force repulsive?

A

Less than 0.5fm

53
Q

What is the force responsible for beta decay?

A

The weak nuclear force

54
Q

What is the decay equation for a down quark?

A

d -> u + electron + anti neutrino

55
Q

What is the decay equation for an up quark?

A

u -> d + positron + neutrino

56
Q

What is the wavelength range for radio waves?

A

> 10^-1m

57
Q

What is the wavelength range for microwaves?

A

10^-3 - 10^-1m

58
Q

What is the wavelength range for infra red?

A

7x10^-7 - 10^-3m

59
Q

What is the wavelength range for visible light?

A

4x10^-7 - 7x10^-7m

60
Q

What is the wavelength range for ultra violet?

A

10^-8 - 4X10^-7m

61
Q

What is the wavelength range for X rays?

A

10^-10 - 10^-8m

62
Q

What is the wavelength range for the overlap between gamma rays and x rays?

A

10^-13 - 10^-10m

63
Q

What is the wavelength range for gamma rays?

A

<10^-13m

64
Q

What two contrast media are used for x rays? Why?

A

Barium and iodene due to their large atomic number (attenuation coefficient is proportional to atomic number ^3)

65
Q

Advantages of CAT scans over x rays?

A
  • 3d image
  • can more easily distinguish between soft tissues
66
Q

Disadvantages of CAT scans over x rays?

A
  • Longer and more expensive
  • Leads to longer ionising exposure
  • Movements from the patient can blur the slice
67
Q

What is a medical tracer or radiopharmaceutical? Examples?

A

A radioisotope combined with other chemicals to ensure it reaches the target organ. Fluorine-18 (beta plus) and Technetium-99m (gamma)

68
Q

How are x rays produced (short answer)

A

The deceleration of electrons

69
Q

How are x rays produced (long answer)

A

Connecting a heater to a high voltage power supply, producing fast moving electrons through thermionic emission. These travel through a vacuum (so they don’t interact with air) to the target metal (such as tungsten), where they hit it and are decelerated, producing an x ray

70
Q

What is intensity proportional to?

A

Amplitude^2

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