A thin semi-circular ring of radius r has a positive charge q distributed uniformly over it. The net field `vecE` at the centre O is

Options

A. `(q)/(2pi^(2)epsilon_(0)r^(2))bar(j)`
B. `(q)/(4pi^(2)epsilon_(0)r^(2))bar(j)`
C. `-(q)/(4pi^(2)epsilon_(0)r^(2))bar(j)`
D. `-(q)/(2pi^(2)epsilon_(0)r^(2))bar(j)`

Answer

4

Explanation

`F=(1)/(4piepsilon_(0))(Qq)/(r^(3))=mromega^(2),omega=(2pi)/(T)`