In Millikans oil drop experiment, an oil drop of radius r charge q falls under the gravity with a terminal velocity V_g and moves up with a terminal velocity V_e in the uniform vertical electric field of intensity E. If η is coefficient of viscosity of air, the charge of oil drop is

An explosion of atomic bomb releases an energy of 7.6x10¹³J.If 200 MeV energy is released on fission of one ²³⁵U atom the number of uranium atoms undergoing fission,and the mass of uranium used in the bomb is

A photo-cathode is irradiated in turn by light of wavelengths 4000 A⁰ and 6200 A⁰ respectively. The ratio of the stopping potentials in the two cases is found to be 2:1. The work function of the photo-cathode is nearly

An electron beam moving with a speed of 2x10⁷ms^-1 enters a magnetic field of induction 3x10^-3T, directed perpendicular to its direction of motion. The intensity of electric field applied so that the electron beam is undeflected due to the magnetic field is

An intrinsic semi conductor has 10¹⁸/m³ free electron and is doped with pentavalent impurity of 10²⁴/m³.Then the free electrons density order increases by

The wave length of the K_αline for an element of atomic number 43 is λ.Then the wavelength of the K_αline for an element of atomic number 29,is

When a monochromatic light of frequency v is incident on a metal, stopping potential is V₀. Frequency of the incident light for which stopping potential becomes 2V₀ is

in a half wave rectifier output is taken across a 90 ohm load resistor. If the resistance of diode in forward biased condition is 10 ohm, the efficiency o rectification of ac power into dc power is

The rate constant of the reaction at temperature 200K is 10 times than the rate constant at 400K.The activation energy of the reaction is

In a p-n junction the depletion region is 400nm wide and electric field of 5x10⁵Vm^-1 exists in it. The minimum energy of a conduction electron, which can diffuse from n-side to the p-side is