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Physics > Module 5: Newtonian world and astrophysics > Flashcards

Module 5: Newtonian world and astrophysics Flashcards

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1
Q

Absolute or thermodynamic scale of temperature

A

Is independent of the properties of any specific substance. Measured in kelvin, K.

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2
Q

Absolute zero (0K)

A

Is the temperature at which a substance has minimum internal energy; this is the lowest limit for temperature.

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3
Q

Thermal equilibrium

A

Objects in contact at the same temperature are in thermal equilibrium; this means that there is no net heat flow between them.

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4
Q

The kinetic model of matter

A

All matter is made up of very small particles (atoms, molecules or ions) which are in constant motion. The model allows us to explain the properties of matter and changes of phase in terms of the arrangement of the particles, the motion of the particles and the attractive forces between them.

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5
Q

Internal energy

A

The sum of the randomly distributed kinetic and potential energies of all the atoms or molecules within a system.

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6
Q

Brownian motion

A

The random movement of small visible particles suspended in a fluid (e.g. smoke particles in air) due to collisions with much smaller, randomly moving atoms or molecules in the fluid.

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7
Q

Specific heat capacity, c

A

The amount of energy needed to raise the temperature of 1kg of the substance by 1K. The units are J kg^-1 K^-1.

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8
Q

Specific latent heat of fusion, L_f

A

The amount of energy required to change the phase of 1kg of a substance from a solid to a liquid.

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9
Q

Specific latent heat of vaporisation, L_v

A

The amount of energy required to change the phase of 1kg of a substance from a liquid to a gas.

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10
Q

Mole

A

One mole of any substance is the amount of substance that contains as many particles as exactly 12.0g of carbon-12. One mole of a substance will contain 6.02x10^23 particles. This number is known as the Avogadro constant and has the symbol N_A. N_A = 6.02x10^23 mol^-1.

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11
Q

Avogadro constant

A

The number of particles in one mole of a substance. This constant has the symbol N_A. N_A = 6.02x10^23 mol^-1.

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12
Q

An ideal gas

A

A gas that has internal energy only in the form of random kinetic energy.

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13
Q

Mean squared speed, c^2

A

The mean value of the square of velocity c for a large number of gas particles (atoms or molecules) moving randomly in a gas. The bar indicates an average.

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14
Q

Root mean square (r.m.s.) speed

A

The square root of the mean square speed.

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15
Q

Boyle’s law

A

The volume of a fixed mass of gas is inversely proportional to the pressure exerted on the gas, under conditions of constant temperature.
pV= constant under conditions of constant temperature.
If we have a gas at p1 and a volume V1 and we change the conditions so that it has a new pressure p2 and a new volume V2, then we can say that p1V1=p2V2.

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16
Q

The equation of state of an ideal gas (the ideal gas equation)

A

Links the pressure of a gas (p) with the volume (V), molar gas constant (R), number of moles of gas (n) and temperature (T): pV=nRT

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17
Q

Boltzmann constant, k

A

A constant used when relating the temperature of the gas to the mean translational kinetic energy of the particles in the gas. It can also be thought of as the gas constant for a single molecule, k= 1.38x10^-23 JK^-1.

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18
Q

One radian

A

The angle subtended at the centre of a circle when the arc is equal in length to the radius of the circle.

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19
Q

Time period, T

A

The time taken in seconds for one complete circular path.

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20
Q

Angular velocity, ω

A

The rate of angular rotation, measured in radians per second, rad s^-1.

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21
Q

Centripetal acceleration

A

The acceleration of an object moving with uniform circular motion. The size of the acceleration is given by a=v^2/r where v is the speed of the object and r is the radius of the circle, or a=ω^2r where ω is the angular velocity. The centripetal acceleration is directed radially inwards towards the centre of the circle, perpendicular to the velocity vector at any instant.

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22
Q

Centripetal force

A

The resultant force on an object, acting towards the centre of the circle, causing it to move in a circular path.
The equation for the centripetal force F is F=mv^2/r ; F=mω^2r.

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23
Q

Displacement, x

A

Distance moved by an object from its equilibrium (or rest) position; may be positive or negative.

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24
Q

Amplitude, x_0

A

The maximum displacement (will always be positive).

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25
Q

Frequency, f

A

The number of oscillations per unit time at any point.

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26
Q

Period, T

A

Time taken for one complete pattern of oscillation at any point.

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27
Q

Angular frequency, ω

A

The product 2πf or alternatively ω= 2π/T (unit of rads^-1).

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28
Q

Phase difference,ϕ

A

The fraction of a complete cycle or oscillation between two oscillating points, expressed in degrees or radians.

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29
Q

Simple harmonic motion

A

A body will oscillate with simple harmonic motion if it’s acceleration is directly proportional to its displacement from a fixed point and always directed towards that fixed point.

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30
Q

Isochronus

A

The period of an object with SHM is isochronus; this means that it is constant and independent of the amplitude of the oscillation.

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31
Q

Damping

A

Damping forces reduce the amplitude of an oscillation with time, due to energy being removed from the oscillating system.

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32
Q

Free oscillations

A

Occur when there is no external, periodic force. The system oscillates at its natural frequency.

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33
Q

Natural frequency

A

The frequency at which a system will oscillate when undergoing free oscillations.

34
Q

Forced oscillations

A

Occur when an external force or driving force is applied to keep the body oscillating. The system oscillates at the frequency of the driving force that is causing the oscillations.

35
Q

Driving frequency

A

The frequency of the driving force applied to an oscillating object.

36
Q

Resonance

A

Forced oscillations occurs when the driving frequency is equal to the natural frequency of the system being forced to oscillate. This results in the body oscillating at its natural frequency and maximum amplitude.

37
Q

Gravitational field

A

The region around a body in which other bodies will feel a force due to the mass of the body.

38
Q

Gravitational field lines

A

They show the shape of the field and the direction of the field line at a point is the direction in which a small mass would move when placed at that point.

39
Q

Gravitational field strength

A

The gravitational field strength at any point in a gravitational field is the force acting per unit mass at that point, g=F/m. Units are N kg^-1.

40
Q

Newton’s law of gravitation

A

States that the gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their separation.

41
Q

Kepler’s third law

A

States that the square of the period of a planet orbiting the Sun is proportional to the mean radius of its orbit cubed: T^2 ∝ r^3. Kepler’s law also applies to other planetary systems, to the orbits of moons around planets and to binary stars.

42
Q

Geostationary orbit

A

An orbit of the Earth made by a satellite that has the same time period and orbital direction as the rotation of the Earth (i.e. 24 hours) and is in the equatorial plane.

43
Q

Gravitational potential

A

Gravitational potential at a point in a gravitational field is defined as the work done in moving unit mass from infinity (where the gravitational potential is zero) to that point. The unit it J kg^-1.

44
Q

Gravitational potential energy

A

The gravitational potential energy of a mass m in a gravitational field depends on its position in the field. For a radial field around a point or spherical mass M, the gravitational potential energy at a distance, r, from M is defined as -GMm/r. The unit is joules (J).

45
Q

Escape velocity

A

The escape velocity from a point in a gravitational field is the minimum launch velocity required to move an object from that point to infinity.

46
Q

Nuclear fusion

A

The process of two nuclei joining together and releasing energy from a change in binding energy.

47
Q

Gravitational collapse

A

The inward movement of material in a star due to the gravitational force caused by its own mass. Star formation is due to the gradual gravitational collapse of a cloud of gas and dust. Gravitational collapse occurs in a mature star when the internal gas and radiation pressure can no longer support the stars own mass.

48
Q

Radiation pressure

A

Due to the momentum of photons released in fusion reactions, and acts outwards (in the direction of energy flow).

49
Q

Gas pressure, p

A

Is related to the temperature, T, and volume, V, of a gas using pV=nRT, and also to the mean square speed of the gas atoms using pV=1/3Nmc^2. Gas pressure acts in all directions at a point inside a gas, such as inside a star.

50
Q

Main sequence star

A

A star in the main part of its life cycle, where it is fusing hydrogen to form helium in its core. The main sequence stars are shown as a curved band on a plot of a star’s luminosity against temperature (Hertzsprung-Russell diagram).

51
Q

Red giant

A

A star in the later stages of its life that has nearly exhausted the hydrogen in its core and is now fusing helium nuclei. It is bigger than a normal star because it’s surface layers have cooled and expanded.

52
Q

White dwarf

A

The end product of a low-mass star, when the outer layers have dispersed into space. A white dwarf is very dense, with a high surface temperature and low luminosity.

53
Q

Planetary nebula

A

An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life.

54
Q

Electron degeneracy pressure

A

The pressure that stops the gravitational collapse of a low-mass star (below the Chandrasekhar limit of 1.4 solar masses). This is the pressure that prevents a white dwarf star from collapsing.

55
Q

Chandrasekhar limit

A

The maximum possible mass for a stable white dwarf star and is equal to 1.4 times the mass of our sun. White dwarfs with masses above this will collapse further to become neutron stars or black holes.

56
Q

Red super giant

A

A star that has exhausted all the hydrogen in its core and has a mass much higher than the Sun.

57
Q

Supernova

A

A huge explosion produced when the core of a red super giant collapses.

58
Q

Neutron star

A

The remains of the core of a red super giant after it has undergone a supernova explosion. It is incredibly dense and composed mainly of neutrons.

59
Q

Black hole

A

The core of a massive star that has collapsed almost to a point. Black holes are very dense and very small, with a gravitational field so strong that light cannot escape (the escape velocity is greater than the speed of light).

60
Q

Hertzsprung-Russell (HR) diagram

A

A luminosity-temperature graph.

61
Q

Luminosity

A

The luminosity of a star is the total energy that the star emits per second.

62
Q

Continuous spectrum

A

A spectrum that appears to contain all wavelengths over a comparatively wide range.

63
Q

Energy levels

A

Energy levels inside an atom are the specific energies that electrons can have when occupying specific orbits. Electrons can only occupy these discrete energy levels and cannot exist at other energy values between them.

64
Q

The emission line spectrum

A

The emission line spectrum of an element is the spectrum of frequencies of electromagnetic radiation emitted due to electron transitions from a higher energy level to a lower one within an atom of that element. Since there are many possible electron transitions for each atom, there are many different radiated wavelengths. A line spectrum consists of a series of bright lines against a dark background.

65
Q

An absorption line spectrum

A

The pattern of dark lines in a continuous spectrum from a light source and is caused by light passing through an absorbing medium such as gas. The dark lines represent the wavelengths that are absorbed.

66
Q

A transmission diffraction grating

A

A glass surface having a large number of very fine parallel grooves or slits, and used to produce optical spectra by diffraction of transmitted light.

67
Q

Maxima

A

Regions of brightness which will be seen when the path difference between overlapping waves is equal to a whole number of wavelengths, i.e. nλ=dsinθ, where n=1,2,3…

68
Q

Wien’s displacement law

A

States that λmax ∝ 1/T or λmaxT= constant (2.89x10^-3m K), where T is temperature on the absolute (Kelvin) scale. It is used to estimate the peak surface temperature of a star from the wavelength at which the star’s brightness is maximum.

69
Q

Stefan’s law

A

Relates the luminosity L of a star (The radiation flux emitted from the surface of a star) with its absolute temperature T: L= 4πr^2σT^4 where the constant, σ, is known as Stefan’s constant and has a value of 5.67x10^-8 Wm^-2K^-4.

70
Q

The astronomical unit (AU)

A

The mean distance from the centre of the Earth to the centre of the Sun.

71
Q

Parsec

A

A unit of distance that gives a parallax angle of one second of arc (1/3600 of a degree), using the radius of the Earth’s orbit (1 AU) as the baseline of a right-angled triangle. 1 parsec is approximately equal to 3.1x10^16.

72
Q

Stellar parallax

A

Is the apparent shifting in position of a star viewed against a background of distant stars when viewed from different positions of the Earth, such as different positions of the Earth’s orbit around the Sun.

73
Q

Light-year

A

The distance travelled by light in one year. One light-year is approximately equal to 9.5x10^15m.

74
Q

The Doppler effect or Doppler shift

A

The change in wavelength caused by the relative motion between the wave source and an observer. For electromagnetic radiation of frequency f and wavelength λ, the Doppler equation is Δλ/λ ≈ Δf/f ≈ v/c where c is the speed of light.

75
Q

Red shift

A

The apparent increase in wavelength of electromagnetic radiation caused when the source (e.g. a star) is moving away, relative to the observer.

76
Q

Hubble’s law

A

States that the recessional velocity, v, of a galaxy is directly proportional to its distance, d, from the Earth.

77
Q

The Hubble constant H_0

A

The constant of proportionality in the equation  v ≈ H0d. The SI unit for H0 is s^-1, but it can also be quoted in kilometres per second per megaparsec (kms^-1Mpc^-1).

78
Q

Cosmic microwave background radiation (CMBR)

A

Microwave radiation received from all over the sky originating from after the Big Bang, when the universe had cooled to a temperature near 3000 K. As the universe has expanded this radiation is now just a faint microwave glow with a peak wavelength corresponding to a temperature of 2.7 K (the same as the temperature of the universe).

79
Q

The Big Bang Theory

A

States that the universe was created from a single ‘point’ where all of the universe’s current mass was situated. At the time of its creation, the universe was much smaller, hotter and denser than it is now. Time and space were both created at the instant of the Big Bang.

80
Q

The cosmological principle

A

States that on a large scale the universe is isotropic (the same in all directions) and homogenous (of uniform density as long as large enough volume is considered).

81
Q

Dark matter

A

Matter which cannot be seen and that does not emit or absorb electromagnetic radiation. It is not detected directly, but is detected indirectly based on its gravitational effects relating to either the rotation of galaxies or by gravitational lensing of starlight.

82
Q

Dark energy

A

A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies by the exertion of a negative pressure. It is not detected directly, but we know it exists because we now know the universe is accelerating as it expands.

Physics (6 decks)

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