7- Quantum behaviour Flashcards
What is a photon?
An electromagnetic wave of frequency, f, emitted and absorbed in quanta of energy, E, where E=hf.
Define intensity of light.
The amount of energy transferred per meter squared per second.
Define threshold frequency.
The minimum frequency of light that will eject photoelectrons from a given surface, varying with material.
Define the work function.
The amount of energy required to remove an electron from a metal surface.
When do atoms release photons?
When an electron falls from a higher energy level to a lower energy level.
Photons with higher energy will have what level of frequency and wavelength?
Higher frequency.
Shorter wavelength.
What is a line spectra?
The wavelengths of light emitted from an element when its electrons lose energy.
What is an LED, and how does it work?
A light emitting diode is a semiconducting device which allows current to flow in one direction. It releases photons when electrons move from one side to the other and falls down energy levels.
How do you calculate the energy change of an electron moving across an LED?
ΔE= Vq
Where q is the charge of an electron and V is the striking potential difference.
What is the relationship between the probability of arrival of a photon and the length of a phasor.
probability is directly proportional to the square of resultant phasor length.
Relating to phasors, where is the focus of a lens?
The point where phasor arrows all have made the same number of rotations.
Describe how you would determine the Planck constant.
- For light emitting diodes of varying wavelengths of light, measure the striking p.d. using a voltmeter in parallel with the LED. Do this whilst in a fairly dark room for highest contrast.
- Calculate the energy of photons emitted via: E=qV
- Calculate frequency of light, using wavelength of LED given by manufacturer and the speed being C.
- Plot photon energy (y) and frequency (x).
- The planck constant will be the gradient of the line.
Give reasons for uncertainty in the practical determination of the Planck constant.
The LED’s will emit light over a range of wavelengths, not just a singular wavelength. It is also tricky to accurately determine the striking p.d.
Describe what electron diffraction looks like, with a thin layer of atoms acting as a ‘natural’ diffraction grating.
A pattern of concentric circles.
Explain how electron diffraction is evidence for electrons showing wave like behaviour.
If electrons were particles, they would cause a central bright region with no concentric circles. Diffraction shows that electrons diffract through slits in the same manner as light (waves).
What is de Broglie’s equation?
λ=h/(mv)
