A Bianchi type-III string cosmological models is investigated in scalar-tensor Brans-Dicke theory of gravity (Phys. Rev. 124, 925, 1961). For an exact solution of modified Einstein 's field equations (EFEs), we assumed time varying nature of deceleration parameter (DP) along with relation between scale factor and time, given by a(t)=[tet)]1/n , and n are non-negative constants. It is noticed from study that the power index has their own significance on the string cosmological models. It is also analyzed that the string tension density () is an increasing function of time whereas the energy density() and the cosmological constant () are decreasing functions of time and converges to small value at present time. and n are non-negative constants.
The proton is a positively charged massive particle.Therefore it has both gravitational field and electromagnetic field. So, in this work special attention is given toEinstein’s gravitational field equations and Maxwell’s electromagnetic field equations.The four dimensionalmetric tensoris used here to solve this problem. The four-dimensional line elementis developed in such a way that the metric is solved in two separate ways. The solutionsfor two fieldsgive some suitable results. Later the formula is extended for the large massive body and gives an interesting resultthat life cannot survive in a planet of mass just greater than1.21 timemass of Jupiter planet.