Question

Two point like charges of same magnitude but opposite signs are fixed to either end of the base of an isosceles triangle as figure shows. The electric field intensity at the midpoint M between the charge has a magnitude E_M. The electric field intensity directly above the midpoint at point P has magnitude E_P. The ratio of these two field magnitude is E_M : E_P = 27. Find the value of cosa

• A. $\frac{1}{3}$
• B. $\frac{1}{6}$
• C. $\frac{1}{2}$
• D. $\frac{1}{9}$

Answer 1

Answer: (A)

$\frac{1}{3}$

Answer 2

E_M = $\frac { \mathrm { kq } \times 2 } { \mathrm { r } ^ { 2 } \cos ^ { 2 } \alpha }$

E_P =

= $\frac { 1 } { \cos ^ { 3 } \alpha }$ = 27

cos a = $\left( \frac { 1 } { 27 } \right) ^ { 1 / 3 }$ ̃ cos a = 1/3