Chapter 13: Quantum Physics Flashcards
What are Photons?
Photons are small packets of energy called quanta, a different way to to describe the nature and properties of Electromagnetic Radiation that the particle model cannot.
What is the equation to calculate the energy of a photon?
To calculate the energy of a photon, the equation is:
E = hf, Energy of photon = Planck’s Constant x Frequency of the electromagnetic radiation
What is the adjusted equation for energy of a photon in terms of its wavelength?
The adjusted equation for energy of a photon, containing the speed of light and wavelength is:
E = hc / λ , Energy = Planck’s Constant x Speed of Light / Wavelength of EM wave
(where f = c / λ)
How do you convert energy from the unit Joules to electron-Volts?
To convert energy from joules to electron volts, divide the energy (J) by the elementary charge (1.6x10^-19).
When given p.d., times the P.d. by the elementary charge.
W = VQ —-> W = Ve
What is the definition of the electron-Volt?
The electron-Volt is the energy transferred to and from an electron as it passes through a potential difference of 1V.
What is the Photoelectric Effect?
The photoelectric effect is the emission of photoelectrons from the surface of a metal when electromagnetic radiation above the threshold frequency is incident on the metal. Caused when photons of EM Radiation collide with electrons on the surface in a one-to-one interaction.
How does the gold-leaf electroscope experiment work?
The gold-leaf electroscope experiment works by charging a metal plate using a cathode. The metal plate which is connected to a gold leaf through a metal stem will become negatively charged and the gold leaf will start to repel from the metal stem due to being negatively charged. If a piece of zinc is placed on the negatively charged metal plate and UV light is shone on the zinc, the metal plate will lose its negative charge due to the photoelectrons (that gave the metal plate a negative charge) being emitted through the zinc leading to the leaf falling back to the metal stem. This shows that electrons can be emitted from a metal if an EM wave above the threshold frequency is incident on the metal.
What were the three key observations from the photoelectric effect?
From the photoelectric effect, three key observations were:
- Photoelectrons are only emitted if the incident radiation is above the threshold frequency. If the radiation is below a certain frequency, no electrons would be emitted regardless of intensity. (Due to each electron requiring a certain amount of energy to be emitted).
- If the incident radiation is above the threshold frequency, the emission of photoelectrons were instantaneous (happens with no time delay).
- If the incident radiation was above the threshold frequency, increasing intensity will increase the number of electrons emitted (due to more photons colliding with more electrons) but not kinetic energy. Increasing the frequency of the incident radiation will increase the kinetic energy of the photoelectrons.
What is the definition of ‘work function’?
Work function is defined as the minimum energy required for an electron to be emitted from the surface of the metal.
What happens to the excess energy after the energy was used for the work function?
If there was remaining energy after the electron has been emitted (due to the work function), the energy would be converted to kinetic energy due to conservation of energy.
What is the equation for conservation of energy for an emitted photon?
For an emitted photon, the equation for the energy would be:
E = Work Function + Kinetic Energy (max)
OR
hf = Work Function + Kinetic Energy (max)
Why is the kinetic energy in the conservation of energy equation referred to as Maximum KE?
The remaining kinetic energy is referred to as maximum KE due to their position relative (how close or far) to the positive ions within the metal, since electrons closer to positive ions will take more energy due to stronger force of attraction.
What is the equation for the straight line graph of KE (max) against frequency (hertz)?
For a straight line graph of KE max against frequency, the equation would be:
KE (max) = hf - work function
y = m x
(rearranged from hf = work function + KE max).
The y-intercept would be the negative of the work function.
What is meant by wave-particle duality?
Wave particle duality is the idea that matter can behave as both a wave and a particle due to matter having properties of each form.
What is the de broglie wavelength equation?
The de broglie wavelength equation is:
λ = h / p, Wavelength = Planck’s Constant / Momentum of the particle.
What is the equation that links p.d. on an LED to the energy of emitted photons?
The equation that links p.d. on an LED to the energy of emitted photons is:
eV = hf OR eV = hc / λ
(Where ‘V’ is the threshold voltage of the LED).
What is the equation for a V against 1/λ straight line graph?
For a straight line graph of V against 1/λ, the equation would be:
V = (hc / e) 1/λ
y = m x
