Quantum Physics Flashcards
Give me the energy of a photon (formula)
E = hf
Blue LEDs photons are…
Higher energy and with a higher strike voltage
LEDs and Planck’s Constant formula
eV=hc/lambda
What is eV?
Electron-volt. 1eV is the energy transferred when one electron travels through a p.d. of 1V.
What is the photoelectric effect?
When a photon strikes the surface of a metal and removes an electron in a one-to-one interaction, by giving it enough energy to overcome its work function.
Classical theory = increasing intensity…
Increases K.E of emitted photoelectrons because energy is proportional to amplitude squared
Quantum theory = increasing intensity…
K.E remains constant, rate of emission increases
Classical theory = time delay
Exists because electrons gain energy over time from wave
Quantum theory = time delay
Doesn’t exist because there is a one-to-one interaction photon-to-electron
Quantum theory = frequency increases…
K.E of photons increases because E=hf.
What is the threshold frequency (f0)?
The minimum frequency of photon needed for an electron to overcome work function.
What happens if the work function isn’t overcome?
Metal heats up
Measuring the energy of photo-electrons formula?
K.E.max=hf - Φ
What graph do you plot in experiment to measure h?
Voltage against 1/λ
What charge does an electroscope plate initially have?
Negative
What is the de Broglie wave?
a probability wave - the likelihood of finding a particle at a point, directly proportional to the amplitude squared
The wave associated with a moving electron is an electromagnetic wave. True or false?
False
electrons can produce rings on a
fluorescent screen beyond a graphite sheet. Explain.
diffraction observable because gaps/atoms are similar to wavelength of
electrons
regular pattern of atoms acts as a grating
constructive interference to produce pattern on screen
When working out what pd is used to accelerate electrons, which formula?
1/2mv^2 = eV, where e is charge on an electron.
