A flat surface having an area of [tex]$3.2 \, m^2$[/tex] is rotated in a uniform electric field of magnitude [tex]$E = 6.2 \times 10^5 \, N/C$[/tex]. Determine the electric flux through this area when the (i) electric field is perpendicular to the surface and (ii) electric field is parallel to the surface.

A. [tex]$1.98 \times 10^6 \, N \cdot m^2 / C$[/tex]; [tex][tex]$1.72 \times 10^6 \, N \cdot m^2 / C$[/tex][/tex]
B. [tex]$9.98 \times 10^5 \, N \cdot m^2 / C$[/tex]; [tex]$1.72 \times 10^6 \, N \cdot m^2 / C$[/tex]
C. [tex][tex]$1.98 \times 10^6 \, N \cdot m^2 / C$[/tex][/tex]; [tex]$9.98 \times 10^6 \, N \cdot m^2 / C$[/tex]
D. [tex]$1.98 \times 10^6 \, N \cdot m^2 / C$[/tex]; [tex][tex]$0$[/tex][/tex]
E. [tex]$0$[/tex]; [tex]$1.72 \times 10^6 \, N \cdot m^2 / C$[/tex]



Answer :

To understand the problem, recall the formula for electric flux ([tex]\( \Phi_E \)[/tex]). The electric flux through a surface is given by:

[tex]\[ \Phi_E = E \cdot A \cdot \cos(\theta) \][/tex]

where:
- [tex]\( E \)[/tex] is the electric field strength,
- [tex]\( A \)[/tex] is the area of the surface,
- [tex]\( \theta \)[/tex] is the angle between the electric field and the normal (perpendicular) to the surface.

Let's solve the problem in two parts:

### (i) When the electric field is perpendicular to the surface:

When the electric field is perpendicular to the surface, the angle [tex]\( \theta = 0^\circ \)[/tex]. The cosine of 0 degrees is 1 ([tex]\( \cos(0^\circ) = 1 \)[/tex]).

Hence, the electric flux [tex]\( \Phi_E \)[/tex] in this situation can be calculated as:

[tex]\[ \Phi_E = E \cdot A \cdot \cos(0^\circ) = E \cdot A \cdot 1 = E \cdot A \][/tex]

Given:
- [tex]\( E = 6.2 \times 10^5 \, \text{N/C} \)[/tex]
- [tex]\( A = 3.2 \, \text{m}^2 \)[/tex]

[tex]\[ \Phi_E = 6.2 \times 10^5 \, \text{N/C} \times 3.2 \, \text{m}^2 = 1984000 \, \text{N} \cdot \text{m}^2 / \text{C} \][/tex]

So, the electric flux when the electric field is perpendicular to the surface is:

[tex]\[ 1.98 \times 10^6 \, \text{N} \cdot \text{m}^2 / \text{C} \][/tex]

### (ii) When the electric field is parallel to the surface:

When the electric field is parallel to the surface, the angle [tex]\( \theta = 90^\circ \)[/tex]. The cosine of 90 degrees is 0 ([tex]\( \cos(90^\circ) = 0 \)[/tex]).

Hence, the electric flux [tex]\( \Phi_E \)[/tex] in this case can be calculated as:

[tex]\[ \Phi_E = E \cdot A \cdot \cos(90^\circ) = E \cdot A \cdot 0 = 0 \][/tex]

So, the electric flux when the electric field is parallel to the surface is:

[tex]\[ 0 \, \text{N} \cdot \text{m}^2 / \text{C} \][/tex]

Combining both parts, the answer is (D):

[tex]\[ \boxed{1.98 \times 10^6 \, \text{N} \cdot \text{m}^2 / \text{C} ; 0} \][/tex]