Quantum Flashcards
What is the work function?
The minimum energy required for electrons to be liberated.
What is the threshold frequency?
The minimum frequency of light photons required to get the work function, using E=hf (The photoelectric effect)
What happens if the frequency is less than the threshold frequency?
No electrons are liberated
What happens if the frequency equals the threshold frequency?
Electrons are liberated but with no kinetic energy
What happens if frequency is greater than the threshold frequency?
Electrons are liberated with kinetic energy
How does intensity affect the liberation of electrons?
If f is less than threshold frequency then it has no effect as no electrons can be liberated as there is not enough energy. If frequency is greater than or equal to the threshold frequency increasing the intensity increases the number of electrons liberated
What is the photoelectric effect equation?
Work function = h x threshold frequency
Therefore,
hf = work function+ max KE
On a graph of kinetic energy against frequency, what is the y-intercept?
The work function
On a graph of kinetic energy against frequency, what is the x-intercept?
Threshold frequency
On a graph of kinetic energy against frequency, what is the gradient?
h, Planck’s constant
In wave-particle duality, what gives evidence for waves acting as waves?
Reflection, refraction, diffraction
In wave-particle duality, what gives evidence for waves acting as particles?
The photoelectric effect
In wave-particle duality, what gives evidence for particles acting as waves?
Electron diffraction
In wave-particle duality, what gives evidence for particles acting as particles?
Classical (eg Newtonian) Physics
What is the De Broglie wavelength?
Every moving particle with mass will have an associated wavelength:
Wavelength = h/p = h/mv
What name is given to the first energy level?
Ground state
What are absorption spectral lines?
Black lines that show where energy has been absorbed from during excitation
What do emission spectral lines show?
Coloured lines show the photons of certain frequencies emitted during de-excitation.
Define 1 Joule.
1 joule of energy is transferred when 1 coulomb of charge passes through a potential difference of 1 volt
Define 1 election volt.
The energy for 1 electron to pass through a potential difference of 1 volt
How does the amount of energy change as you move further from the ground state?
It increases
Explain excitation by photon absorption
- A photon passed through an electron in the atom
- The electron only absorbs the photon if it has the exact right amount of energy needed to excite
- If the photon has the correct energy, the electron absorbs it and moves
- If the photon does not have the right amount of energy, it passes through and the electron remains in the same state
Explain excitation by electron collision.
- A free electron collides with an electron in an atom
- The electron in the atom absorbs the amount of energy it needs to move energy levels from the moving electron
- The electron in the atom moves
- The free electron is rebounded if it has remaining energy
Explain de-excitation.
Electrons need to be on the lowest possible energy level
If there is a space on a lower energy level after another electron has been excited or liberated, the electron will move down to the lower level, emitting a photon of energy as it moves
The photons frequency depends on the amount of energy released in order to move
What is an example of a use of electron excitation?
Fluorescent lamps
How does a fluorescent lamp work?
- Fluorescent substances have UV sensitive pigments (phosphor)
- An electric current is passed through a fluorescent lamp, electrons in the current collide with atoms of mercury vapour in the lamp
- The electrons must have sufficient energy for the collisions to excite the electrons in the mercury
- When the mercury electrons de-excite, they emit UV photons
- The tube is coated in a phosphor which will absorb the photons, exciting their electrons
- When these electrons de-excite they emit photons of visible light
What is the maximum kinetic energy during the photoelectric effect?
Ek max is the maximum kinetic energy of the photoelectrons
What is an ion?
an atom which has the same number of protons and neutrons in the nucleus but has gained or lost an electron from its orbital to become positively or negatively charged
How many joules is 1 electron volt?
1.6x10^-19
What do the lines on spectra correspond to?
the discrete energy levels of the atom
Why does momentum affect the diffraction pattern produced?
smaller momentum will result in a longer wavelength. The diffraction or spread of a wave passing through a slit depends on the wavelength- the longer the wavelength, the more the light spreads out. electrons with smaller momentum will produce a more diffuse diffraction pattern
What were the 2 opposing greek views of how matter was formed and which was more believed? (and explain each)
- Democritus’s “atomos” theory that everything was made up of small indivisible atomos. by mixing different atomos you could make different materials.
- Aristotle’s Alchemy theory that everything was made of the four elements - earth wind fire and water.
Aristotle’s theory was preferred for approx 2000 years.
What was John Dalton’s theory of how matter was formed, and in which year was it hypothesised?
in 1808, he said matter was made of elements, which were pure substances which contained no other elements. he said each element was made of a different type of atom. he created the “billiard ball” model as he said atoms were tiny solid spheres.
What did J.J Thomson hypothesise?
in 1987 J.J Thomson said the atom was a positively charged sphere with negatively charged electrons embedded within it. this was the first mention of subatomic particles. (“plum pudding” model)
Explain Rutherford’s gold foil experiment.
Rutherford shot positively charged alpha particles at a sheet of gold foil. He detected the number of particles to pass through the foil. he discovered, while most passed straight through, some were partially deflected and others completely rebounded. this all took place in a vacuum as not to be disturbed by air particles,
What did Rutherford propose from the results of his experiment?
the atom was mostly empty space with a positively charged centre which he named the nucleus. and the electrons must orbit the nucleus
What must be done for a scientific theory to be valid?
it must have repeatable experimental results supporting the hypothesis
