Particles and Waves

Question 1

Absolute refractive index

Answer 1

the absolute refractive index (or more simply, the refractive index), n, of a medium is the ratio sinθ1/sinθ2
where θ1 is in a vacuum, and θ2 is in the medium

Question 2

Angle of incidence

Answer 2

the angle between the incident ray and the normal

Question 3

Angle of refraction

Answer 3

the angle between the refracted ray and the normal

Question 4

Atomic mass units (u)

Answer 4

by definition one twelfth of the mass of a carbon-12 nucleus

Question 5

Atomic number

Answer 5

the number of protons in an atomic nucleus. It is this number that determines the element

Question 6

Binding energy

Answer 6

the energy needed to split a nucleus into its separate nucleons

Question 7

Chain reaction

Answer 7

when a nucleus undergoes fission it releases neutrons that can go on to collide with other nuclei, causing further fission reactions. If there is a sufficient concentration of suitable nuclei, the process becomes self-sustaining.

Question 8

Coherent waves

Answer 8

coherent waves are waves that have the same frequency, speed and have a constant phase relationship

Question 9

coherent waves are waves that have the same frequency, speed and have a constant phase relationship

Answer 9

part of a spectrometer that is used to produce a parallel beam of light

Question 10

Critical angle

Answer 10

the maximum value of the angle between the normal and the ray in glass, θ glass, for which refraction can occur

Question 11

Diffraction

Answer 11

an effect that causes waves to bend as they go past the end of an obstacle or through a small gap in a barrier

Question 12

Dispersion

Answer 12

the process of splitting up light into its constituent colours

Question 13

Electromagnetic waves

Answer 13

the spectrum of waves that includes radio, visible light, X-rays etc

Question 14

Excited state

Answer 14

any atomic energy level higher than the ground state

Question 15

Fission

Answer 15

the splitting of a large atomic nucleus into smaller fragments, with the resultant release of excess energy

Question 16

Frequency

Answer 16

the number of complete cycles of a wave passing a given point in a given time, usually per second. Frequency is measured in hertz (Hz) where 1 Hz = 1 wave per second.

Question 17

Fundamental unit of charge

Answer 17

e; the magnitude of charge carried by one electron or one proton. Equal to 1.60 x 10-19 coulombs

Question 18

Grating

Answer 18

a transparent slide of glass or plastic that has a very large number of equally-spaced grooves machined on to its surface. Each groove acts as a source for coherent beams of light.

Question 19

Ground state

Answer 19

the lowest energy level of an atom

Question 20

Induced fission

Answer 20

the deliberate splitting of a large nucleus caused by the collision of the nucleus with a neutron

Question 21

Ionisation level

Answer 21

the energy level at which an electron can break free from an atom

Question 22

Irradiance

Answer 22

the power per unit area of radiation incident on a surface

Question 23

Isotopes

Answer 23

different forms of the same element. The isotopes of an element contain the same number of protons but have different numbers of neutrons.

Question 24

Line absorption spectrum

Answer 24

a spectrum that consists of narrow dark lines across an otherwise continuous spectrum

Question 25

Line emission spectrum

Answer 25

a spectrum consisting of narrow lines of light, the position of which depend on the substances producing the light

Question 26

Magnetic field

Answer 26

a magnetic field is a region in which a moving charge experiences a magnetic force

Question 27

Mass defect

Answer 27

the difference between the mass of a nucleus and the total mass of an equal number of individual nucleons

Question 28

Mass number

Answer 28

the total number of nucleons in the nucleus of an atom

Question 29

Monochromatic

Answer 29

radiation consisting of a single frequency

Question 30

Monochromatic light

Answer 30

light of one wavelength (and therefore one colour)

Question 31

Normal

Answer 31

a line drawn at right angles to a surface or the boundary between two different media

Question 32

Nucleon

Answer 32

the general term for protons and neutrons

Question 33

Nuclide

Answer 33

the nuclei of one particular isotope. These nuclei all have the same atomic number and mass number.

Question 34

Path difference

Answer 34

the difference in path lengths of two sets of waves

Question 35

Period

Answer 35

the time to make one complete wave. Period is measured in seconds.

Question 36

Photocathode

Answer 36

the terminal from which electrons will be emitted due to the photoelectric effect

Question 37

Photoelectric effect

Answer 37

the emission of electrons from a metal due to the effect of electromagnetic radiation

Question 38

Photoelectrons

Answer 38

free electrons produced by the photoelectric effect

Question 39

Photoemission

Answer 39

the emission of electrons from a material caused by light shining on it

Question 40

Photon

Answer 40

the particle of electromagnetic radiation

Question 41

Principle of reversibility

Answer 41

the principle of reversibility states that a ray of light will follow the same path in the opposite direction when it is reversed

Question 42

Radioactive decay series

Answer 42

a chain of radioactive decays as a radioactive element changes to eventually become a stable, non-radioactive element

Question 43

Radioisotope

Answer 43

short for radioactive isotope

Question 44

Radionuclide

Answer 44

short for radioactive nuclide

Question 45

Spectrometer

Answer 45

an instrument that can make precise measurements of the spectra produced by different light sources

Question 46

Spontaneous fission

Answer 46

the random splitting of a large atomic nucleus due to the internal processes within the nucleus

Question 47

Stopping potential

Answer 47

the minimum voltage required to reduce photoelectric current to zero

Question 48

Threshold frequency

Answer 48

the minimum frequency of electromagnetic radiation that will cause photoemission for a particular substance

Question 49

Total internal reflection

Answer 49

when a ray of light travelling in a more dense substance meets a boundary with a less dense substance at an angle greater than the critical angle, the ray is not refracted but is all reflected inside the more dense substance

Question 50

Valence shell

Answer 50

the atomic energy level that contains the outermost electrons of the atom. It is the electrons in this shell that determine the chemical reactions between elements.

Question 51

Work function

Answer 51

the minimum energy required to cause photoemission from a particular substance