Question

The number of electric field lines crossing an area $\Delta S$ is $n_{1}$ when normal of $\Delta \vec{S}$ is parallel to $\vec{E}$, while number of field lines crossing same area is $n_{2}$ when normal of $\Delta \vec{S}$ makes an angle of $30^{\circ}$ with $\vec{E}$. Then

• A. $n_{1} = n_{2}$
• B. $n_{1} > n_{2}$
• C. $n_{1} < n_{2}$
• D. cannot say anything

Answer 1

Answer: (B)

For first case: $\phi=E \Delta S \cos 0^{\circ}=E \Delta S$
For second case: $\phi=E \Delta S \cos 30^{\circ}$
Thus, in first case the flux crossing the surface is more than the flux crossing through surface in $2^{\text {nd }}$ case, so $n_{1} > n_{2}$