• Evacuated tube, emitter, collector.

• Photosensitive emitter emits electrons when illuminated.

• Electrons flow from emitter to collector.

• Voltage difference enables electron flow..

• Observe current from emitted electrons.

Stopping Potential: $\phi_0 V_0$

• When monochromatic light strikes a photosensitive material, it emits electrons.

• The released electrons create an electron current from the photosensitive material.

• A voltage difference is maintained to facilitate electron flow from the emitter to the collector.

• The experiment measures current produced by electrons striking the collector, confirming the effect.

$e \phi_0=k_{\text {max }}$ of the electrons that are emitted

$k_{\text {max }}$ : Maximum kinetic Energy

• Intensity of Radiation

• Wavelength of Radiation

• The material that is used

Intensity is important $\epsilon_0 \vec{E}^2$ in the energy density

Thermionic emission: Temperature

Wavelength is not an important parameter as for as $\phi_0$ is concerned.

Electro Magnetic wave is oscillatory electric field.

Forced oscillations.

Forced oscillations.

• Material Used.$\rightarrow$ Temprature

• Material Used.$\rightarrow$ Temperature density of the electrons etc.

$\frac{K_{\max }+\phi_0}{V}=C$ ${[C]=M L T^{-1}=[E][t]}$ C is independent of

• Material

• Frequency

• Amplitude (Intensity)

• C is a Universal Constant

$\frac{K_{max} + e V_0}{\nu}=C$

$V_0 = \phi_0$

${\nu}$ = Frequency

$C$ = Is a Constant.

Universal Constant

Does not depend on any experimental Condition.

$M L^2 ~ T ^{-1} : \text { Energy } \times \text { time. }$

Missing in the Slide

Work function of elements, in units of electron volt (eV).

$~$

Work function Contd Silver

Polycrystalline Silver

• 100 : 4.64 eV

• 110 : 4.52 eV

• 111 : 4.74 eV

Conclusions

1. That there exists for each exciting frequency v, above a certain critical value, a definitely determinable maximum velocity of emission of corpuscles.
2. That there is a linear relation between V and v.
3. That $\frac{dV}{dv}$ or the slope of the V v line is numerically equal to h/e.
4. That at the critical frequency $\nu_0$ at which $v = 0$, $p = h \nu_0,$ i.e., that the intercept of the $V v$ line on the v axis is the lowest frequency at which the metal in question can be photoelectrically active.
5. That the contact E.M.F. between any two conductors is given by the equation.

$\text {Contact E.M.F.} = h/e(\nu_0 - \nu_0^\prime)-(V_0 - V_0^\prime).$

Ack: Wikicommons

Intensity - Frequency Interplay

1. Minimum frequency required for photoemission

2. Proportional to Intensity beyond the minimum frequency

3. No emission below the minimum frequency

4. Linear Relation between the frequency and the stopping potential

$ma = \frac{G M m}{r^2}$

What carries energy in light?

Maxwell

$U=\varepsilon \vec{E}^2 \Longrightarrow\langle U\rangle=\frac{\varepsilon}{2} \vec{E}_0^2$

$U_{rad} = \epsilon_0 \vec{E}^2$

$\rightarrow \frac{\epsilon_0}{2} ~\vec{E}_0^2$

$\vec{E} = \vec{E}_0 \cos (\vec{k}. ~\vec{r} - \omega t)$

No frequency dependence

Minimum Energy required depends on frequency for photo emission