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Physics Part 3 (Particle Physics; Wave–Particle Duality (De Brogile's…
Physics Part 3
Particle Physics; Wave–Particle Duality
De Brogile's idea (wave)
Wavelength of electrons to small to diffract except via graphite atoms proving that elections are waves too
λ = h/mv; for wavelength of subatomic particle
Einstein's idea (particles) i.e. photo-electric
effect
E = hf; Energy of a photon
Size of a nucleus can be calculated using:
sin θ = λ/b; where b is diameter of nucleus
Not part of the course
Modern Physics
Astrophysics
Medical Imaging Techniques
Atomic physics: absorption and emission spectra
Photons can be absorbed by atoms (increases internal energy) or emitted (reduces internal energy)
Ionisation energy of electron from potential well is the energy needed for the electron to escape the atom
Quantum physics: photoelectric effect (PE)
Energy of a photon
E = hf
Maximum kinetic energy of electron:
1/2mv^2 = E
k
= hf-Φ. Note hf here is energy of photon
Because taking away the energy of the work function
means only kinetic energy of the electron remains once it is released from the metal
Kinetic energy can also be used to work out the speed of the released electron as above
Note-Through conservation of energy:
Kinetic energy of electron = Energy of photo
Conversion of energy of photon
from joules to electron volts:
Energy of photon/1.6x10^-19
1 eV = 1.6x10^-19J
Planck constant (h) comes from
the gradient of the graph of:
Kinetic energy of photo-electrons v frequency of light
Plank constant: h = 6.3x10^-34 Js
Threshold frequency
is frequency at which
photons have enough energy to cause the photo-
electric effect i.e. lift the electron
out of the metal
Work function, Φ = hf
o
.
f
o
is threshold frequency
It is thus the minimum energy needed by an electron
to escape a metal
The wavelength of light can be worked
out by combining:
E = hf
c = fλ
Practical uses: Solar panels!
Electromagnetism: Magnetic fields and forces. Electromagnetic induction
Magnetic fields always flow from
North to South and never cross!
Electromagnetic Fields and Spectrum: Uses and hazards of ionising radiations
Physical Optics: Interference and diffraction