Question

A cylindrical source of light which emits radiation radially (from a curved surface) only, placed at the center of a hollow, metallic cylindrical surface, as shown in the diagram.
The power of the source is $90$ watt and it emits light of wavelength $4000A$ only. The emitted photons strike the metallic cylindrical surface which results in the ejection of photoelectrons. All ejected photoelectrons reach the anode (light source). The magnitude of photocurrent in amp is $[Given:h=6.4\times {10}^{-34}J/sec]$.

Answer 1

Power is 90 W. It corresponds to 90 J/s.
The energy of one photon is $E=\frac{hc}{\lambda }=\frac{6.4\times {10}^{-34}\times 3\times {10}^8}{4000\times {10}^{-10}}=4.8\times {10}^{-19}$

Number of photon emitted per second $=\frac{90}{4.8\times {10}^{-19}}=1.875\times {10}^{20}$

Number of photoelectrons emitted per second $=\frac{120}{360}\times 1.875\times {10}^{20}=6.25\times {10}^{19}$

Electric current $=6.25\times {10}^{19}\times 1.602\times {10}^{-19}=10A$