Find out pressures at point `A` and `B`. Also find angle `theta`. A zig zag tube open at `n`, having liquis of densities `rho_(1), rho_(2)` and `rho_(3)` is placed in a vertical plane as shown in figure. (The pressue at `M` is equal to atmospheric pressure).

Explanation

Pressure at `A` is `P_(A)=P_(atm)-rho_(1)glsintheta`
Pressure at `B` is `P_(B)-P_(atm)+rho_(2)gh`
But `P_(B)` is also given by `P_(B)=P_(A)+rho_(3)glsintheta`
Hence `P_(atm)+rho_(2)gh=P_(a)+rho_(3)glsintheta`
`implies P_(atm)=rho_(2)gh=P_(atm)-rho_(1)glsintheta+rho_(3)glsintheta`
`implies sintheta=(rho_(2)h)/((rho_(3)-rho_(1))l)`