Definitions for Physics A2

Question 1

Absolute zero

Answer 1

With the temperature at which a system has a minimum internal energy equivalent to -273.15c

Question 2

Acoustic impedance

Answer 2

Acoustic impedance Z is the product of the density of the substance and the speed of sound in that substance

Question 3

Activity

Answer 3

The rate of decay or disintegration of nuclei in a radioactive sample

Question 4

Amplitude

Answer 4

The maximum displacement of a particle from its equilibrium position

Question 5

Angular displacement

Answer 5

The angle through which an object moves in a circle

Question 6

Angular frequency

Answer 6

The rate of change of angle expressed in radian per second. angular frequency (ω) = 2π/T

Question 7

Astronomical unit

Answer 7

The average distance of the Earth from the sun

Question 8

Avogadro constant

Answer 8

The number of particles in one mole of any substance (6.02x10^23)

Question 9

Big bang

Answer 9

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

Question 10

Binding energy

Answer 10

The minimum external energy required to separate all the neutrons and protons of an nucleus

Question 11

Black hole

Answer 11

A remnant of a massive star formed as a result of matter collapsing to a point (singularity) The density of a black hole is so intense that even light cannot escape from it

Question 12

Boyles Law

Answer 12

The pressure exerted by fixed mass of gas is inversely proportional to to its volume, provided the temperature of the gas remains constant

Question 13

Braking radiation

Answer 13

X-rays produced when electrons are decelerated

Question 14

Capacitance

Answer 14

The ratio of charge stored by capacitor to the potential difference across it

Question 15

Carbon dating

Answer 15

A technique used to date relics of using the carbon-14 isotope

Question 16

Centripetal force

Answer 16

The net force acting on an object moving in a circle; it is always directed towards the centre of the circle

Question 17

Chain reaction

Answer 17

And exponential growth of a fission reaction caused by the increasing flux of neutrons causing fission

Question 18

Chandrasekhar limit

Answer 18

The maximum mass of the white dwarf - about 1.4 solar masses

Question 19

Characteristic radiation

Answer 19

Very intense x-rays produced in an x-ray tube having specific wavelengths that depend on the target metal

Question 20

Charles’s law

Answer 20

The volume occupied by gas at constant pressure is directly proportional to its thermodynamic temperature (absolute)

Question 21

Closed system

Answer 21

A system of interacting objects where there are no external forces

Question 22

Closed universe

Answer 22

And model of the universe in which gravitational force is strong enough to hold its expansion and reverse the process towards a big crunch

Question 23

Collimated beam

Answer 23

A parallel sided beam of radiation

Question 24

Collimator

Answer 24

A device for producing a parallel beam of radiation

Question 25

Compton scattering

Answer 25

An interaction between an x-ray photon and an electron in which the photos are scattered with a longer wavelength

Question 26

Computerised axial tomography

Answer 26

A technique where x-rays are used to image slices of the body in order to produce a computerised 3-D image

Question 27

Conservation of momentum

Answer 27

In a closed system, when bodies interact, the total momentum in any specified direction remains constant

Question 28

Contrast

Answer 28

In a high contrast image there is a big difference in brightness between bright and dark areas

Question 29

Contrast media

Answer 29

Material such as Bury and that is the absorb x-rays. Contrast medium is used to reveal the outlines or edges of soft tissues in an x-ray image

Question 30

Control rods

Answer 30

Rods of a neutron absorbing material are used to reduce the rate of a nuclear chain reaction

Question 31

Coolant

Answer 31

A substance used to transfer thermal energy from the core of a nuclear reactor

Question 32

Cosmic microwave background radiation

Answer 32

Electromagnetic radiation in the microwave region of the spectrum that corresponds to a temperature of the universe of 2.7 K

Question 33

Cosmological principle

Answer 33

The principal states that the universe has the same large-scale structure when observed from any point in the universe

Question 34

Coulombs law

Answer 34

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

Question 35

Count Rate

Answer 35

The number of particles (beta or alpha) or gamma-ray photons detected per unit time by Geiger-Müller tube. Can't rate is always a fraction of the activity of a sample

Question 36

Critical density

Answer 36

The density of the universe that will give rise to a flat universe, given by the equation 3Ho^2/8πG

Question 37

Damped

Answer 37

Describes an oscillary motion with the amplitude decreases with the time due to energy losses

Question 38

Dark energy

Answer 38

A form of energy thinly distributed throughout the universe which may be causing the expansion of the universe to accelerate

Question 39

Dark matter

Answer 39

Matter that emits or reflects little electromagnetic radiation, making it difficult to detect

Question 40

Decay constant

Answer 40

The constant λ for an isotope that appears in the equation A=λN. It is equal to the probability of an isotope decaying per unit time interval