Question

St ㄟ the Pars bl s The $ face siin at y Assume"s has Po sytive orientation You hqve Ss/ is'ulua.Ja aleS wav dan , which surac which is Jonaand

Answer 1

Here, it is given that has positive orientation.

Now observe the field vector $\vec{F} = y\hat{j} - z\hat{k}$ . Its y-component is positive (as $0\le{y}\le1$ ) and z-component is both positive and negative(depending on z value). Now direction vector of surface $S_2$ is $\hat{j}$ which results in positive flux. Hence $S_2$ is upward surface. Conversely for surface $S_2$ the direction vector dotted with $\vec{F}$ cancels out giving zero flux due to symmetry. Hence $S_1$ is downward surface.