modern physics definitions

Question 1

electron

Answer 1

an electron is an invisible quantity of charge that orbits the nucleus of an atom

Question 2

thermionic emission

Answer 2

thermionic emission is the emission of electrons from the surface of a hot metal

Question 3

work function

Answer 3

the work function of a metal is the minimum energy needed to remove the loosest electrons from the surface of that metal

Question 4

x-rays

Answer 4

x-rays are high frequency electromagnetic radiation which are produced when high speed electrons, in a cathode ray tube, strike a dense metal target, that has a high melting point

Question 5

photoelectric effect

Answer 5

the photoelectric effect (photoemission) is the emission of electrons from the surface of a metal when electromagnetic radiation of a suitable frequency falls on it

Question 6

photon

Answer 6

a photon is a packet of electromagnetic radiation

Question 7

threshold frequency

Answer 7

the threshold frequency for any metal is the minimum frequency needed to cause photoelectric emission

Question 8

cathode rays

Answer 8

cathode rays are streams of high speed electrons moving from the cathode

Question 9

electron volt (eV)

Answer 9

the electron volt is the energy lost or gained by an electron when it accelerates through a potential difference of one volt

Question 10

protons

Answer 10

protons are positively charged nucleons, they have the same size charge as the electron

Question 11

neutrons

Answer 11

neutrons are electrically neutral nuclons, they have slightly more mass than protons

Question 12

atomic number

Answer 12

atomic number is the number of protons in the nucleus of an atom

Question 13

atomic mass numer

Answer 13

atomic mass number is the number of protons plus neutrons in the nucleus of an atom

Question 14

isotopes

Answer 14

isotopes are atoms with the same atomic number but different atomic mass number due to the number of neutrons in the nucleus

Question 15

radioactivity

Answer 15

radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation

Question 16

ionisation

Answer 16

ionisation is the charging of a neutral atom or molecule when it loses or gains one or more electrons

Question 17

penetration

Answer 17

penetration is the distance the radiation travels through a medium

Question 18

radioisotope

Answer 18

a radioisotope is an unstable isotope of an element that decays spontaneously, emitting radiation

Question 19

alpha emission

Answer 19

alpha emission is the emission of a helium nucleus from a large atom

Question 20

beta emission

Answer 20

beta emission is the emission of an electron when a neutron decays into a proton and electron

Question 21

gamma emission

Answer 21

gamma emission is the emission of high energy photons from an unstable nucleus

Question 22

activity

Answer 22

the activity of a radioactive source is the rate of emissions from that source

Question 23

half-life

Answer 23

the half-life of a radioactive isotope is the time taken for half of the nuclei in a given sample to decay

Question 24

nuclear fission

Answer 24

nuclear fission is the splitting of a large nucleus into two smaller nuclei with emission of neutrons and release of energy

Question 25

nuclear fusion

Answer 25

nuclear fusion is the combining of two small nuclei to form a single larger nucleus with the release of energy

Question 26

chain reactions

Answer 26

chain reactions are reactions where at least one neutron is released during each fission reaction

Question 27

critical mass

Answer 27

critical mass is the minimum amount of fissile material needed in order for chain reactions to occur

Question 28

radiation

Answer 28

radiation is the emission of particles of matter or photons of energy

Question 29

background radiation

Answer 29

background radiation is radiation that comes from environmental sources including the Earth's crust, the atmosphere, cosmic rays and radioisotopes