Intensity of point-like source at 1000 m is I. it is changed to 16I, then required distand will be

Options

A. 250 m
B. 500 m
C. 750 m
D. 800 m

Answer

A, B

Explanation

Relation of intensity at distance r from point like source,
`I=(phi)/(4 pi r^2)`
`therefore I prop (1)/(r^2)`
`therefore (I)/(I.)=((r.)/(r))^2`
`therefore (I)/(16 I)=(r.^2)/((1000 m)^2)`
`therefore r.^2=((1000 m)^2)/(16)`
`therefore r.=(1000m)/(4)`
`therefore r.=250` m