To solve this problem we will apply the concepts related to dynamic equilibrium. The vertical component of the tension is equivalent to the centripetal Force while the horizontal component of the tension is equivalent to the weight, therefore we will have the two equations,


Our values are,


Therefore if we divide both equation we have,

Replacing,




Therefore the angle required is 15.18°
Answer is power outlet in your house
Bohr is the scientist you are looking for my friend...;)
Solution :
We assume that there is a ring having a charge +Q and radius r. Electric field due to the ring at a point P on the axis is given by :




If we put an electron on point P, then force on point e is :

![F= \frac{-eKQx}{(r^2+x^2)^{3/2}}= \frac{-eKQx}{r^3[1+\frac{x^2}{r^2}]^{3/2}}](https://tex.z-dn.net/?f=F%3D%20%5Cfrac%7B-eKQx%7D%7B%28r%5E2%2Bx%5E2%29%5E%7B3%2F2%7D%7D%3D%20%5Cfrac%7B-eKQx%7D%7Br%5E3%5B1%2B%5Cfrac%7Bx%5E2%7D%7Br%5E2%7D%5D%5E%7B3%2F2%7D%7D)
If r >> x , then 
Then, 


Compare, a = -ω²x
We get,




It is mainly used to give facts about living organisms