## Photoelectric effect
+
+
### Planck's equation
$$E=hf,\quad f={c \over \lambda}$$
- rate of photoelectron release is proportional to intensity of incident light
- shining light on a metal "bombards" it with photons
- no time delay
+- one photon releases one electron
#### Work function and threshold frequency
$\phi$ is work function ("latent" energy)
Gradient of a frequency-energy graph is equal to $h$
-y-intercept is equal to $\phi$
+y-intercept is equal to $\phi$
+voltage $V$ in circuit is indicative of max kinetic energy in eV
#### Stopping potential $V_0$
+
+Smallest voltage to achieve minimum current
+
$$V_0 = {E_{K \operatorname{max}} \over q_e} = {{hf - \phi} \over q_e}$$
## Wave-particle duality
- therefore, stable orbits are those where circumference = whole number of e- wavelengths
- if $2\pi r \ne n{h \over mv}$, interference occurs when pattern is looped and standing wave cannot be established
+
+
### Photon momentum
$$\rho = {hf \over c} = {h \over \lambda}$$
### Absorption
-- Black lines in spectrum show light not reflected
+- Black lines in spectrum show light not reflected
+- Frequency of a photon emitted or absorbed can be calculated from energy difference: $E_2 – E_1 = hf$ or $= hc$
### Emission
+
+
+
- Coloured lines show light being ejected from e- shells
- Energy change between ground / excited state: $\Delta E = hf = {hc \over \lambda}$
- Bohr's model describes discrete energy levels
- EMR is absorbed/emitted when $E_{\operatorname{K-in}}=\Delta E_{\operatorname{shells}}$ (i.e. $\lambda = {hc \over \Delta E_{\operatorname{shells}}}$)
## Light sources
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+
+
- **incandescent:** <10% efficient, broad spectrum
- **LED:** semiconducting doped-Si diodes
- - most electrons in *valence band* (energy level)
where $\sigma n$ is the uncertainty of $n$
-**$\sigma E$ and $\sigma t$ are inversely proportional$**
+**$\sigma E$ and $\sigma t$ are inversely proportional**
Therefore, position and velocity cannot simultaneously be known with 100% certainty.
**Quantum mechanical model** - electron clouds rather than discrete shells (electrons are not particlces). We can only calculate probability of an electron being observed at a particular position
+Newton's and Einsteins models work together
+
+### Photon-electron interaction
+
+When a photon collides with an electron, momentum is transferred to electron.
+
+$$\rho_{\text{photon}}={h \over \lambda}$$
+$$E=\rho c$$
+
+
+
774 abc melbourne
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