Atomic and Nuclear Phenomena

Question 1

What is the photoelectric effect?

Answer 1

when light of a sufficiently high frequency is incident on a metal in a vacuum, the metal atoms emit electrons

Question 2

What is threshold frequency?

Answer 2

fT - the minimum frequency of light that causes ejection of electrons

Question 3

What is the equation for energy of a photon?

Answer 3

E = hf
E = energy of a photon of light
h = Planck's constant (6.626x10-34 J)
f = frequency of light

Question 4

What is the equation for maximum kinetic energy of the ejected electron?

Answer 4

Kmax = hf - W
W = work function

Question 5

What is the work function?

Answer 5

the minimum energy required to eject an electron and is related to the threshold frequency of that metal
W = hfT

Question 6

What is the relationship between energy, matter and speed of light?

Answer 6

E = mc^2

Question 7

What is strong nuclear force?

Answer 7

the force that holds protons and neutrons together; compensates for the repulsive electromagnetic force between protons but only works over short distance

Question 8

What is the weak nuclear force?

Answer 8

also contributes to stability of nucleus but one millionth as strong

Question 9

What is the mass defect?

Answer 9

the difference between the theoretical mass of an element and the actual mass

Question 10

What is the atomic number?

Answer 10

Z - corresponds to the number of protons in the nucleus

Question 11

What is the mass number?

Answer 11

A - number of protons plus neutrons

Question 12

What is fusion?

Answer 12

when small nuclei combine to form a larger nucleus

Question 13

What is fission?

Answer 13

process by which large nucleus splits into smaller nuclei

Question 14

What is radioactive decay?

Answer 14

naturally occurring spontaneous decay of certain nuclei accompanied by the emission of specific particles

Question 15

What is alpha decay?

Answer 15

the emission of an alpha particle - will leave the daughter nucleus with an atomic number two less than the parent and the mass number is four less

Question 16

What is an alpha particle?

Answer 16

42He nucleus - 2 protons, 2 neutrons and zero electrons

Question 17

What is beta decay?

Answer 17

emission of a beta particle - results in same mass number but an atomic number one higher

Question 18

What is a beta particle?

Answer 18

an electron

Question 19

What is a positron?

Answer 19

has the mass of an electron but with a positive charge

Question 20

What is gamma emission?

Answer 20

emission of gamma rays - no change in mass or atomic number, just emission of a gamma ray

Question 21

What are gamma rays?

Answer 21

high energy (high-frequency) photons

Question 22

What is electron capture?

Answer 22

when the element captures an electron so the atomic number becomes one less; opposite of beta decay

Question 23

What is half life?

Answer 23

sample is the time it takes for half of the sample to decay

Question 24

What is the equation for exponential decay?

Answer 24

n = n0*e^-lambda*t
n0 = number of undecayed nuclei at time t = 0
lambda = decay constant
n = radioactive nuclei that have not yet decayed in a sample

Question 25

How is the decay constant related to half-life?

Answer 25

decay constant = 0.693/T(1/2)