Quantum Flashcards
What is the work function?
The minimum amount of energy required to release a photoelectron from the surface of a metal
What determines the specific energy levels available?
- The ion/atom
- Ions of the same atom have different energy levels
What is the electron volt?
Energy of an electron with change e accelerated by a p.d. of 1V
What does quantum mean in physics?
A distinct/specific amount
What is a photoelectron ?
An electron which interacts with a proton of sufficient energy and escapes the atom or ion
When is the intensity of light irrelevant in the photoelectric effect?
The intensity is irrelevant if the frequency of the photon does not have sufficient energy to satisfy the work function and there is a ono-one interaction between electrons and photons
How is light treated in the photoelectric effect and flame test?
As district packets (quanta) of energy
How does additional energy affect a photoelectron?
An additional energy to the work function is transferred into kinetic energy
Explain the flame test
Energy is absorbed by the atom which manifests as an excited electron. When the electron inevitable drops to a lower energy level it releases energy as a photon
What is the energy of a photon given by?
E = hf
How is current produced in a photocell?
Light of the correct frequency incident on the plate causes photoelectrons to escape and a current flows
What is the intensity of a light source?
Number of photons released per second
How does intensity affect current?
- Determines number of photoelectrons per second
- Determines current
What is the stopping voltage?
The battery voltage that prevents max KE photoelectrons from reaching the anode resulting in 0 current
How do we determine the stopping voltage?
Apply an opposing p.d. to the current until it is 0
Why can the frequency of the photons change the current?
- Higher frequency photons are more penetrative so more deeply rooted photoelectrons are released
- Photoelectrons which previously did not have enough KE to escape now do
How is current affected if the frequency is further increased?
The photons become so penetrating that they pass through the plate and do not interact with electrons, decreasing current.
What is the threshold frequency?
The minimum amount of energy to satisfy the work function
What effect does a supporting p.d. have on the current in a photocell
Does not affect current as it is the number of photoelectrons produced per second, which is dependant on the light intensity and frequency of photons.
What effect does an opposing p.d. have on the current in a photocell?
Reduces the current as the lowest energy photoelectrons are stopped from crossing the photocell.
How do you calculate the threshold frequency?
f = φ / h
How is a current produced in a neon lamp?
- There is a large p.d. across the lamp
- Results in a large electric field from one side of the tube to the other
- This pulls the positive nucleus from a/some negative electrons
- Ionises some of the gas particles
- Allows for a flow of charged particles and a current forms
How is a specific colour produced in a neon lamp?
- Ions and electrons are being accelerated to opposite ends of the tubes
- They will inevitably collide with other atoms in the tubes
- Some will collide quickly after ionisation, so wont have much KE
- Some will collide after accelerating to a high KE
- There is a continuous range of energies of ions and therefore of the atoms they collide into
- Most if not all energy levels are excitable, so spectrum of the chosen gas is visible
How does is fluorescent lamp work?
- Similar to a neon lamp but the chosen gas predominantly emits UV
- A fluorescent coating is applied on the surface of the tube, which has an energy level at the same frequency of UV
