A2 Level Physics Definitions

Question 1

Angular speed

Answer 1

The angular displacement per unit

Question 2

Centripetal force

Answer 2

The resultant force on an object towards the centre of the circle when the object is rotating round that circle at constant speed.

Question 3

Centripetal acceleration

Answer 3

The acceleration of an object towards the centre of the circle when the object is rotating at constant speed round that circle.

Question 4

Gravitational field

Answer 4

A region in space where a mass experiences a gravitational force.

Question 5

Newton’s law of gravitation

Answer 5

Any two point masses attract each other with a force that is directly proportional to the produce of their masses and inversely proportional to the square of their separation.

Question 6

Gravitational field strength

Answer 6

The gravitational field strength at a point is the gravitational force exerted per unit mass on a small object placed at that point.

Question 7

Gravitational potential

Answer 7

The gravitational potential at a point is the work done per unit mass in bringing a point mass from infinity.

Question 8

Geostationary orbit

Answer 8

An orbit of a satellite such that the satellite remains directly above the same point of the Earth at all times.

Question 9

Natural frequency

Answer 9

The frequency at which a body vibrates when there is no (resultant external) resistive force acting on it.

Question 10

Damped

Answer 10

A damped oscillation is an oscillation in which resistive forces cause the energy of the system to be transferred to the surroundings as internal energy.

Question 11

Resonance

Answer 11

Occurs when the frequency of the driving force is equal to the natural frequency of the oscillating system. The system absorbs the maximum energy from the driver and has maximum amplitude.

Question 12

Internal energy

Answer 12

The sum of the random distribution of kinetic and potential energies of the atoms or molecules in a system.

Question 13

Isothermal change

Answer 13

A change of a system in which the temperature remains constant.

Question 14

Specific latent heat of fusion

Answer 14

The amount of heat energy per unit mass needed to convert unit mass of solid to liquid without change in temperature.

Question 15

Specific latent heat of vaporisation

Answer 15

The amount of heat energy per unit mass needed to convert unit mass of liquid to gas without a change in temperature.

Question 16

Ideal gas

Answer 16

A gas that behaves according to the equation pV=Nrt.

Question 17

Kinetic theory of gases

Answer 17

A model based on the microscopic motion of atoms or molecules of a gas.

Question 18

Root-mean-square speed

Answer 18

The square root of the average of the squares of the speeds of all the molecules in a gas.

Question 19

Electric field

Answer 19

Force per unit charge on positive charge

Question 20

Field of force

Answer 20

A region of space where an object feels a force; the force may be gravitational, electric, magnetic and so on.

Question 21

Electric field strength (at a point)

Answer 21

The force per unit charge exerted on a stationary positive charge at that point.

Question 22

Coulomb’s law

Answer 22

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 the distance between them.

Question 23

Electric potential

Answer 23

The electric potential at a point is equal to the work done per unit charge in bringing unit positive charge from infinity to that point.

Question 24

Capacitance

Answer 24

The capacitance of a capacitor is the charge on the plates of the capacitor per unit potential difference across the plates.

Question 25

Diffraction

Answer 25

The spreading of a wave when it passes through the gap or past the edge of an object

Question 26

Photoelectric effect

Answer 26

An interaction between a photon and an electron in a metal, in which the electron is removed from the surface of a metal

Question 27

Photon

Answer 27

A quantum of electromagnetic energy

Question 28

Threshold frequency

Answer 28

The minimum frequency of the incident electromagnetic radiation that would eject electrons from the surface of a metal.

Question 29

Threshold wavelength

Answer 29

The longest wavelength of the incident electromagnetic radiation that would eject electrons from the surface of a metal

Question 30

Work function (energy)

Answer 30

The minimum energy needed by an electron to free itself from the surface of a metal.

Question 31

Ground state

Answer 31

The lowest energy state that can be occupied by an electron in an atom.

Question 32

de Broglie Wavelength

Answer 32

The wavelength associated with a moving particle, given by the equation: l=h/p

Question 33

Mass defect

Answer 33

The difference between the total mass of the individual separate nucleons and the mass of the nucleus.

Question 34

Binding energy

Answer 34

The minimum external energy required to completely separate all the neutrons and protons of a nucleus to infinity.

Question 35

Fission

Answer 35

The process in which a massive nucleus splits into two smaller nuclei.

Question 36

Fusion

Answer 36

The process in which two light nuclei join together to form a heavier nucleus.

Question 37

Decay constant

Answer 37

The probability that an individual nucleus will decay per unit time interval.

Question 38

Activity

Answer 38

The rate of decay of nuclei of a radioactive source. The units of activity is the becquerel, Bq.

Question 39

Exponential decay

Answer 39

The decrease of a quantity where the rate of decrease is proportional to the value of quantity.

Question 40

Half-life

Answer 40

The half-life t1/2 of an isotope is the mean time taken for half of the active nuclei in a sample to decay.

Question 41

Intensity

Answer 41

Power per unit cross sectional area.

Question 42

Attenuation

Answer 42

The gradual decrease of intensity of radiation as it passes through a medium.

Question 43

Image intensifiers

Answer 43

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

Question 44

Contrast media

Answer 44

Materials, such as barium, which are good absorbers of X-rays; they are used to show the edges of soft tissues in X-ray images

Question 45

Computerised axial tomography (CAT or CT)

Answer 45

A technique in which X-rays are used to image the body in order to produce a three-dimensional image

Question 46

Piezo-electric crystal

Answer 46

A material that produces an e.m.f. when it is stressed, causing its shape to change. Also, when a voltage is applied across it in one direction, it changes its dimensions slightly.

Question 47

Acoustic impedance

Answer 47

The product of the density of the substance and the speed of the ultrasound in the substance.

Question 47

Piezo-electric effect

Answer 47

The production of an e.m.f. across a crystal by putting the crystal under stress. The opposite effect is applying a p.d. across the crystal causing it to change shape.

Question 48

Impedance matching

Answer 48

The use of a gel to reduce the intensity of unwanted, reflected ultrasound between two materials. The gel has a similar acoustic impedance to the reflecting material.

Question 49

Radiotracer

Answer 49

A substance that consists of radioactive material that is attached to a natural chemical, such as glucose.

Question 50

Line of response

Question 51

Tesla

Answer 51

newton per ampere per metre where wire is perpendicular to the magentic field