Chapter 13 Quantum Physics Flashcards
What are photons?
Photons are tiny packets of energy. Which show both particle and wave behaviour.
How is the energy of a photon related to its frequency?
They are directly proportional
E=hf
How do you derive the equation including E,h,c and lambda?
Use the wave equation v = f x lambda and substitute in the frequency into E = hf.
What is Planck’s constant?
6.63x10^-34
How do you calculate the energy in one eV?
energy transferred from an electron when it moves through a potential difference of 1V.
What is the charge of an electron?
-1.6 x 10^-19
Why don’t electrons get freed from a metal when visible light is shone on it?
The frequency is too low and hence the wavelength is too high.
What is the proportion of photons to photoelectrons?
1:1
why doesn’t increasing the intensity of light start to release photo electrons if more are hitting the surface of the metal per second?
The photons only have a 1:1 ratio and so multiple photons cannot release one electron.
What is the name for the minimum amount of energy needed to free an electron from the surface of a metal?
The work function.
What is the kinetic energy of a photoelectron if it has only just overcame the work function?
0
Why are some of the electrons not emitted from a metal at the moment the energy of the work function is met?
Lots of the electrons are nearer to the nucleus and will require more energy to overcome the forces it has with the nucleus,
How can you get electrons to diffract?
Pass them through a material with gaps which are similar to its wavelength such as polycrystalline graphite.
What equation links wavelength, momentum and Planck’s constant?
lambda= h/mv
Why is the interference pattern of electrons diffracting made of rings?
The waves are diffracted through the graphite which has layers oriented in different directions and so forms the rings.
What change happens to the maximum kinetic energy of an emitted electron if the intensity of the light is increased?
No change as each photon has the same energy there are just less of them and they interact in a 1:1 ratio.
Define threshold frequency?
The minimum frequency required to free an electron from the surface of a metal;.
What happens to the gradient of an energy frequency graph if the threshold frequency is increased?
The gradient would stay the same which is Planck’s constant.
Explain what is meant by the de Broglie wavelength of an electron?
Electrons are observed to behave like waves where the electron wavelength depends on its momentum.
