65) The specific charge for positive rays is much less than that for cathode rays. This is because

66) The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4 eV. The stopping potential is

67) A stream of electrons enters an electric field with?10⁷ms^?1?at right angle to it. If the strength of field is?3?10⁴V/m³, the magnetic field acting perpendicular to electric field for producing no deflection of the beam is

68) A drop of radius one micron carries a charge of 4 electrons. If the density of oil is 2g/cc, the electric field required to balance it is

69) When a photon of energy 7eV is made incident on a metal then the emitted electron is stopped by a stopping potential of -5.5V. The work function of metal will be