Chapter 4.5 - Quantum Physics Flashcards
Photon model
Light is made of many particles called photons, each of which is a quantum of light energy. A photon will either transfer all or none of its energy
Energy of a photon
E=hf
Electronvolt
The kinetic energy gained by an electron when it is accelerated through a p.d. of 1 volt
Experiment to determine planck’s constant
Connect an LED in series with a variable resistor and in parallel with a voltmeter. Adjust the variable resistor so that only a tiny amount of light is being emitted by the LED. Record the threshold voltage and the wavelength of the light being emitted. Do this with different LEDs of different wavelengths. Plot V against 1/λ and the gradient should be hc/e.
Why the experiment to determine Planck’s constant works
All of the kinetic energy of the electron is transferred to a photon, therefore we can equate the two values
The photoelectric effect
Shining E.M radiation on a metal will instantaneously eject photoelectrons
Experiment to show photoelectric effect
A plate with a gold leaf attached is negatively charged. UV light is shone onto the plate and the photons are ejected, meaning that the gold leaf is no longer repelled and will fall
Significance of the photoelectric effect
Evidence for the particulate nature of light
Photoelectric equation
hf = φ + KE(max)
Work function
The energy needed to eject an electron with 0 KE
Threshold frequency
The minimum frequency at which photoelectrons will be emitted. hf = φ
How is intensity related to maximum KE of ejected electrons
Independent
How is the rate of emitted electrons related to intensity
Proportional
Evidence for wave like behaviour of particles
Electron diffract through the gaps between atoms
Materials that electrons are diffracted through
Polycrystalline graphite
