A clock face has charges `-q, -2q, ,.....-12q` fixed at the position of the corresponding numerals on the dial. The clock hands do not disturb the net field due to point charges. At what time does the hour hand point in the direction of the electric field at the centre of the dial.

Answer

`9.30`

Explanation

`E_(x)=E_(0)+2E_(0) cos 30^(@)+2E_(0) cos 60^(@)=(2+sqrt(3))E_(0)`
`E_(y)=E_(0), tan theta=E_(y)/E_(x)=1/(2+sqrt(3))xx2-sqrt(3), theta=15^(@)`
The hour hand will point towards `9:30`