CBSE Class 12-science Answered

first let us do question no 15,  we know that flux is  given by

phi= electric field(with directiion) dot (.) area vector.

in part "a" of the question,

electric field in along x axis, and area vector of the square is also along x axis,(since it is kept in Y-Z plane), so angle between the normal  to the area and the electric field is zero degree, so

flux through the surface is

phi= electric field multiply  by the area  of the square.

so phi= 3000 multiply by 0.01

          =30, N.square meter/ coulomb.

In second part. the angle between  electric field and the area vector is  60 degrees, so dot product will remove by  cosine of the  angle between them, so net flux is

half of the flux obtained in section a

that is 15N square meter/ coulomb.