Light of wavelength $2.08\times {10}^{-7} \mathrm{m}$ falls on a photo-surface. The stopping voltage is $1.40 \mathrm{V}$. Calculate the largest wavelength of light that will result in emission of electrons from this photo-surface.

The intensity of light incident on a photo-surface is doubled while the wavelength of light stays the same. For the emitted electrons, discuss the effect of this, if any, on $\mathbf{i}$ the energy and $\mathbf{ii}$ the number.

To determine the work function of a given photo-surface, light of wavelength $2.3\times {10}^{-7} \mathrm{m}$ is directed at the surface and the stopping voltage, $V_s$, recorded. When light of wavelength $1.8\times {10}^{-7}\mathrm{m}$ is used, the stopping voltage is twice as large as the previous one. Determine the work function.

Light falling on a metallic surface of work function $3.0 \mathrm{eV}$ gives energy to the surface at a rate of $5.0\times {10}^{-4} \mathrm{W}$ per square metre of the metal's surface. Assume that an electron on the metal surface can absorb energy from an area of about $1.0\times {10}^{-18} {\mathrm{m}}^2$. Estimate how long will it take the electron to absorb an amount of energy equal to the work function.

Light falling on a metallic surface of work function $3.0 \mathrm{eV}$ gives energy to the surface at a rate of $5.0\times {10}^{-4} \mathrm{W}$ per square metre of the metal's surface. Assume that an electron on the metal surface can absorb energy from an area of about $1.0\times {10}^{-18} {\mathrm{m}}^2$. Outline the implications of this.

Light falling on a metallic surface of work function $3.0 \mathrm{eV}$ gives energy to the surface at a rate of $5.0\times {10}^{-4} \mathrm{W}$ per square metre of the metal's surface. Assume that an electron on the metal surface can absorb energy from an area of about $1.0\times {10}^{-18} {\mathrm{m}}^2$. Describe how the photon theory of light explains the fact that electrons are emitted almost instantaneously with the incoming photons. 

From the graph of electron kinetic energy $E_k$ versus frequency of incoming radiation, deduce the critical frequency of the photo-surface.

From the graph of electron kinetic energy $E_k$ versus frequency of incoming radiation, deduce the work function.

What is the kinetic energy of an electron ejected when light of frequency $f=8.0\times {10}^{14} \mathrm{Hz}$ falls on the surface?