The human eye has an approximate angular resolution of `phi = 5.8xx10^(-4)` rad and a typical photo printer prints a minimum of 300 dpi (dots per inch, `= 2.54 cm`). Aminimum distance 'z' should a printed page be held so that one doesnot see the indivdual dots is ______ .

Two metallic plate A and B , each of area 5 xx 10^(-4)m^(2) , are placed parallel to each at a separation of 1 cm plate B carries a positive charge of 33.7 xx 10^(-12) C A monocharonatic beam of light , with photoes of energy 5 eV each , starts falling on plate A at t = 0 so that 10^(16) photons fall on it per sqare mater for every 10^(6) incident photons fall on it per square meter per second Assume that one photoelectron is emitted for every 10^(6) incident photons . Also assume that all the emitted photoelectron are collected by plate B and the work function of plate A remain constant at the value 2 eV Determine (a) the number of photoelectrons emitted up to i = 10s, (b) the magnitude of the electron field between the plate A and B at i = 10 s, and (c ) the kinetic energy of the most energotic photoelectrons emitted at i = 10 s whenit reaches plate B Negilect the time taken by the photoelectrons to reach plate B Take epsilon_(0) = 8.85 xx 10^(-12)C^(2)N- m^(2))

A mercury arc lamp provides 0.10 W of UV radiation at a wavelength of lambda = 2537Å (all other wavelenghts having been absorbed by filters). The cathode of photoelectric device (a photo-tube) consists of potassium and has an effective area of 4cm^(2) . The anode is located at a distance of 1 m from radiation source. The work function for potassium is phi_(0) = 2.22eV . (a) According to classical theory, the radiation from the arc spreads out uniformly in space as spherical wave. What time of exposure to the radiation should be required for a potassium atoms(radius 2 Å) in the anode to accumulate sufficient energy to eject a photo-electron? (b) What is the energy of a single photon from the source? (C) What is the flux of photons(number per second) at the cathode? To what saturation current does this flux correspond if the photo-conversion efficiency is 5% (i.e. if each photon has a probability of 0.05 of ejecting an electron). (d) what is the cutt off potential V_(0) ?