Atomic and nuclear phenomena

Question 1

What is Photoelectric effect

Answer 1

ejection of electrons from the surface of a metal in response to light

Question 2

What is threshold frequency

Answer 2

minimum light frequency necessary to eject an electron from a given metal

Question 3

What is work function and how to calculate it?

Answer 3

Minimum energy required to eject an electron from a metal. Threshold frequency x Planck’s constant(k)

Question 4

How does the energy of an incident photon get transferred to electron that is exiting the metal surface?

Answer 4

higher energy -> higher frequency above the threshold frequency -> more kinetic energy that exiting electron has

Question 5

What do ejected electrons produce?

Answer 5

Current; this current is proportional to intensity of the incident beam of light

Question 6

Explain Bohr model of the atom in terms of absorption and Emission

Answer 6

Energy levels of electrons are discrete, and when low to high -> absorption, and high to low -> emission.

Question 7

How is energy related to frequency?

Answer 7

E = hf

Question 8

What is the maximum kinetic energy of an exiting electron?

Answer 8

KEmax = hf - W; W = hf(threshold)

[Energy of exiting electron - Energy required to remove the electron from the metal surface]

Question 9

How does Fluorescence occur?

Answer 9

when an excited electron comes down to ground state in 2 or more steps, wavelength of the photons emitted in visible spectrum gives fluorescence.

Question 10

What is mass defect?

Answer 10

Difference in mass between bonded nucleons and unbonded nucleons(proton and neutrons). unbonded ones have more mass because no energy is released yet. once bonded, energy is released and is lighter.

Question 11

What are the four fundamental forces of nature?

Answer 11

Strong nuclear force, weak nuclear force, electrostatic force, gravitational force

Question 12

What does Z mean in isotopic notation?

Answer 12

atomic number: proton + neutron

Question 13

What does A mean in isotopic notation?

Answer 13

mass number: proton

Question 14

What is Alpha decay?

Answer 14

emission of alpha particle - helium nucleus.
A-4
Z-4

Question 15

What is Beta negative decay?

Answer 15

Decay of a neutron into a proton, with emission of an electron and an antineutrino.
Z+1

Question 16

What is Beta positive decay?

Answer 16

Proton into a Neutron, emission of positron.

Z-1

Question 17

What is Gamma Decay?

Answer 17

Emission of gamma rays(high energy photons).

Removal of asterisk(*) from the parent nucleus

Question 18

What is Electron Capture?

Answer 18

Electron absorbed into proton -> neutron

Z-1

Question 19

What is Half-life?

Answer 19

amount of time it takes for a sample to decay 50%

Question 20

How to calculate the remaining sample after a number of half life?

Answer 20

(1/2)^n

n = number of half-lives

Question 21

What is exponential decay and its equation?

Answer 21

Rate of decay is proportional to number that remain
dn/dt = -λn
λ: decay constant
dn/dt = rate of decay
λn = rate that remains

Question 22

What is the equation for exponential decay and what does it show us?

Answer 22

n = ni e^-λt

how number of nuclei changes with time

Question 23

How is decay constant related to the half-life?

Answer 23

λ = ln(2) / T(1/2) 
T(1/2) = half life = 0.693
λ = decay constant