The surface charge density of a thin charged disc of radius R is `sigma`. The value of the electric field at the centre of the disc `(sigma)/(2 in_(0))`. With respect to the field at the centre, the electric field along the axis at a distance R from the centre of the disc is

Explanation

The electric field strength on the axis at a distance ..x.. from its centre of uniform charged circular disc is
`E= (sigma)/(2 epsi_(0)) (1- (x)/((x^(2) + R^(2))^(1//2)))`. At centre, `E_(0) = (sigma)/(2 epsi_(0))`
At distance `x= R, E = (sigma)/(2 epsi_(0)) (1-(x)/((x^(2) + R^(2))^(1//2)))= (sigma)/(2 epsi_(0)) (1- (R )/((R^(2) + R^(2))^(1//2)))`
`=(sigma)/(2 epsi_(0)) (1- (1)/(sqrt2)) = (sigma)/(2 epsi_(0)) (0.37) = 0.37 E_(0)`