A unit postive charge of mass 2 kg was kept on point . At time an electric field was switched on such that potential at any point is given by: If the velocity with which it crosses the -axis is in the form: Find + + + .
Clarification : denotes Euler's number , .
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Let us first find the equation of the electric field line which passes through ( 1 , 1 ) .As V = x 2 + y Then electric field E at any point ( x , y ) is given by E = − ∂ x ∂ ( V ) i ^ − ∂ y ∂ ( V ) j ^ − ∂ z ∂ ( V ) k ^ That is E = − 2 x i ^ − 1 j ^ Now let the equation of electric field line be y = f ( x ) . So the tangent to it at any point should also be the angle made by the vector E . So d x d y = 2 x 1 That is d y = 2 x d x Integrating both the sides. ∫ 1 y 2 d y = ∫ 1 x x d x ⇒ 2 ( y − 1 ) = ln x This will be the equation of the field line passing through ( 1 , 1 ) for the given electric field. Let the particle cross the x-axis at point (a,o).Hence 2 ( 0 − 1 ) = ln a ⇒ a = e 2 1 As electrostatic force is conservative in nature. Using energy conservation 2 1 m v 2 = q ( V i n i t i a l − V f i n a l ) v 2 = ( 1 + 1 ) − ( e 4 1 + 0 ) v = e 2 ( 2 e 4 − 1 ) Hence α = 2 , β = 2 , γ = 4 and δ = 1 . So α + β + γ + δ = 9