(3) Quantum Phenomena

Question 1

Suggest evidence that:
i) Electrons have wave properties
ii) EM radiation has particle properties
iii)EM Radiation has wave properties

Answer 1

i) Diffraction
ii) Photoelectric Effect
iii) Double Slit Experiment

Question 2

Define Work Function

Answer 2

Minimum Energy required for electrons to become excited and move up electron shells

Question 3

Context Photoelectric effect:
State and explain effect:
i)Increase in frequency of light:

ii)Increasing the intensity of light

Answer 3

i) Electrons have higher kinetic energy. E=Hf if frequency increases so does energy

ii) More photons released from light source per unit of time. Hence more photoelectrons are being emitted.

Question 4

Define Photons

Answer 4

Discrete packets off light.

Question 5

Formula for Threshold Frequency

Answer 5

F=Work Function/Planck’s Constant

Question 6

Compare excitation and ionisation

Answer 6

Excitation: An atom gaining energy. Electron moving up energy levels. (Further away from nucleus)

Ionisation: An electron is removed from an atom often by high energy collision of another electron.

Question 7

Context: Fluorescent tubes

Describe the process by which mercury atoms become excited in a fluorescent tube

Answer 7

-Fluorescent Tube has flow of electrons
-Which collide with electrons in mercury atom
-This causes Mercury atom’s electrons to become excited and move up energy levels.

Question 8

Context Fluorescent Tubes

What is the purpose of the coating on the inside of the glass of the fluorescent tube?

Answer 8

The phosphorous coating absorbs UV light emitted by mercury vapor, exciting electrons in the phosphor. As these electrons de-excite, they release photons in the visible spectrum, producing light.

Question 9

Context:
Photoelectric effect
Define Threshold Frequency of the incident light.

Answer 9

Frequency required for light to start emitting photons on the metal surface when shone.

Question 10

Absorption Spectrum and Emission Spectrum
i) What do the black lines on both suggest?

ii) Which spectrum would you expect more black lines on?

Answer 10

i) Show frequencies/Wavelengths that were emitted/absorbed.

ii) Expect more lines on emission spectrum.
Greater number of different wavelengths that can be emitted than absorbed.
(All electrons when they absorb have to start on ground state and move to a specific energy level.
However on the way back down they can move any way they want)

Question 11

Difference between Emission and Absorption spectrum.

Answer 11

In absorption atom becomes excited/moves to higher
energy state/level (by absorbing photon). These are seen as “black lines”

In emission atom de-excited/moves to lower energy state
(by emitting photon of specific wavelength)