Photoelectric Effect and Wave Duality Flashcards
What’s threshold frequency
Minimum frequency of photons required to emit electrons from the surface of metal
Describe photoelectric effect
When electromagnetic radiation is fired at a metal, electrons are fired out at a certain frequency of photon
Why does the wave nature not explain photoelectric effect
If you had a low frequency wave and increases the intensity, the work function should be exceeded at some point
What happens when light intensity increases
Number of electrons emitted increases, if frequency is higher than threshold
What happens when frequency of light increases
Photoelectrons gain more kinetic energy after leaving the surface
What are particle-sized packets of light called
Photons
What is stopping potential
Minimum potential required to stop photoelectric emission
What is work function
Minimum energy of photons required for photoelectric emission
What is ionisation
When an atom gains or loses an electron
What is excitation
When an electron moves to a higher energy level by collision or absorption of a “specific energy” of photon
What happens after excitation
The electron de-excites to the lowest level, emitting photons at each drop
Explain how a fluorescent tube works
Electrons fired at mercury atoms causing excitation. These emit UV photons in de-excitation, which is then caught by coating which excites and de-excites producing visible photons
Describe the graph of kinetic energy (y-axis) against frequency of the photons (x-axis)
Linear line, x-intercept as threshold frequency, y-intercept as wave function, gradient is Planck’s Constant.
Ek = hf - ø
What is the electron volt
Work done when an electron is moved through 1V of pd
What is the lowest energy level called in an atom
Ground state
What does the line spectra of hydrogen tell us
Evidense for transitions between discrete energy levels in atoms; hydrogen electrons de-exciting
What suggests that particles have wave properties
Electron diffraction
What is the de Broglie wavelength equation
wavelength = h/mv
What happens if momentum increases
Voltage increases, wavelength decreases and diffraction decreases
How are changes evaluated
Peer review and validated by the scientific community
What is the equation for lasers
Power = nhf
What happens if a photon hits an orbital electron that has energy, which lies between two energy levels
Electrons stays in the ground state as photons must lose all of there energy to excite/ionise
What happens if an electron hits an orbital electron that has energy, which lies between two energy levels
The orbital electron would be excited to an energy level below that energy and the colliding electron would bounce away with the remainder energy
What is the name of collision where kinetic energy is not conserved
Inelastic collision
Explain why kinetic energy of photoelectrons range up to a certain maximum
photons have a fixed energy, these lose all energy in a single interactions, electrons can lose various amounts of energy to escape from the material
What are some observations that show a particle nature of light
Rate of emission depends on intensity and not frequency, kinetic energy depends on frequency, existence of threshold frequency, instantaneous ejection
Explain why wave nature of light can’t explain threshold frequency
Energy depends on intensity for waves, energy needed to eject electrons, you would expect emission would depend on intensity not frequency
Explain why wave nature of light can’t explain instantaneous ejection
Energy is delivered continuously for waves, so low intensity wave would require a certain amount of time to gain enough energy to eject
Explain how Einstein’s photoelectric theory accounts for threshold frequency
Light is made of packets called photons, these affect one electron each, they have energy E=hf, f>(theta/h) for emission
Why are energy levels negative
Energy decreases from 0 as electrons move to lower energy levels
