Definitions

Question 1

Astronomical unit

Answer 1

The average distance of the Earth from the sun

Question 2

Big bang

Answer 2

An event at which a very hot explosion from which time and space evolved - beginning of the universe

Question 3

Chandrasekhar limit

Answer 3

Maximum mass of a white dwarf - About 1.4 solar masses

Question 4

Closed universe

Answer 4

A model in which gravitational forces are strong enough to halt expansion and reverse into a big cruncg

Question 5

Collimator beam

Answer 5

A parallel sided beam of radiation

Question 6

Collimator

Answer 6

A device for producing a parallel beam of radiation

Question 7

Compton scattering

Answer 7

An interaction between X ray photons and an electron in which the photon is scattered with a longer wavelength

Question 8

Contrast media

Answer 8

Materials such as barium that absorb x rays easily and they are used to outline soft tissues

Question 9

Coolant

Answer 9

A substance used to transfer the thermal energy form the core to the water and turbine

Question 10

Cosmological principle

Answer 10

A principle that states that the universe has the same large scale structure when observed from any point in the universe

Question 11

Coulomb’s law

Answer 11

Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of their distances

Question 12

Critical density

Answer 12

The density of the Universe that will make it flat.

3xH / 8pie x G

Question 13

Decay constant

Answer 13

The probability of an isotope decay per unit time interval. A=L x N

Question 14

Electric field strength

Answer 14

The force per unit postive charge

Question 15

Electron degeneracy pressure

Answer 15

Pressure created by closely packed electrons in a white dwarf due to Pauli’s exclusion principle ( Fermi pressure

Question 16

Unit of capacitance

Answer 16

Farad

1 F = C / V

Question 17

Hadrons

Answer 17

Particles consisting of quarks

Question 18

Hubble constant

Answer 18

The ratio of the speed v of a receding galaxy to its distance x from the observer

H0 = v / x

Question 19

Hydrogen burning

Answer 19

4 H -> He + 2e + 2v

Question 20

Image intensifier

Answer 20

A device used to change a low intensity X ray image into a bright visual image

Question 21

Induced nuclear fission

Answer 21

A fission reaction started when a neutron is absorbed by nucleus

Question 22

Larmor frequency

Answer 22

The frequency of precession of nuclei in an external magnetic field

Question 23

Internal energy

Answer 23

The sum of the random distribution of kinetic energies and potential energies of an atom or molecules in a system

Question 24

Lenz’s law

Answer 24

The induced emf is in a direction so as to produce effect which oppose the change producing it

Question 25

Leptons

Answer 25

A group of fundamental particles that includes electrons and the neutrino

Question 26

Magnetic flux and unit

Answer 26

The product of magnetic flux density normal to a circuit and the cross sectional area of the circuit unit Wb

Question 27

Magnetic flux linkage + unit

Answer 27

The product of magnetic flux an the number of turns. | Unit Wb

Question 28

Magnetic flux density

Answer 28

The strength of a magnetic field. B= F/ IxL

Question 29

Metastable

Answer 29

Describes a nucleus in a unstable but relatively long lived state

Question 30

Moderator

Answer 30

A material used in nuclear reactor to down fast moving neutrons so that they have a greater chance of interacting with fissile nuclei

Question 31

Neutrino

Answer 31

An uncharged particle with almost no mass, emitted during beta decay

Question 32

Nuclear fission

Answer 32

The splitting of a nucleus eg U.235 into two fragments and a small number of neutrons

Question 33

Olber's paradox

Answer 33

For an infinite, uniform static universe, the night sky should be infinitely bright because of light received in all directions from stars

Question 34

Open universe

Answer 34

A model of the universe in which gravitational force cannot cannot halt the expansion of matter. The universe will expand forever

Question 35

Parralax

Answer 35

The apparent shifting in a star's position relative to the background stars from earth

Question 36

Photoelectric effect

Answer 36

An interaction between an X ray photon and an electron in which the electron is removed from the atom.

Question 37

Photomultiplier tubes

Answer 37

Devices used in a gamma camera to change the energy of an incident gamma ray photon into an electric pulse

Question 38

Positron

Answer 38

A positively charged particle with mass equal to an electorn

Question 39

Planetary nebula

Answer 39

hot gases and dust blown away form a low mass star as it evolves into a white dwarf ( not to do with planetary formation)

Question 40

PET scan positron emmision tomography

Answer 40

A technique where gamma ray photons from electron-positrons annihilations are detected to produce a 3D image of the body

Question 41

Precession

Answer 41

The movement of the axis of a spinning object

Question 42

Red giant

Answer 42

A star characterised by its cooler surface and extremely large sufrace area

Question 43

Red shift

Answer 43

A star used to describe the shifting of the entire spectrum of a receding source to longer wavelengths.

Question 44

Relaxation time

Answer 44

The time taken for the nuclei to fall back into their lower energy state

Question 45

Solenoid

Answer 45

A lng current carrying coil used to generate a uniform magnetic field within its core

Question 46

Spin

Answer 46

A quantum property of many atomic or sub atomic particles

Question 47

Strong nuclear force

Answer 47

A fundamental force that acts between quarks. More detail on other G485 notes.

Question 48

Supernova

Answer 48

The explosion of a high mass star that leaves a neutron star or a balck hole

Question 49

Super red giant

Answer 49

A red giant formed towards the end of life of a massive star

Question 50

Tesla

Answer 50

Unit for magnetic fluc density | 1T = 1 N / A m

Question 51

Unified atomic mass unit

Answer 51

A convenient unit used for the mass of atomic and nulcear particles 1/12 of carbon 12 1.66x10-27

Question 52

Weak interaction

Answer 52

The nulcear force responsible for beta decay

Question 53

White dwarf

Answer 53

The very hot remnants of a low mass star

Question 54

X-ray tube

Answer 54

A device that produces x rays when accelerated electrons hit a target metal