A small bulb is placed at the bottom of a tank containing water to a depth of 80cm. What is the area of the surface of water through which light from the bulb can emerge out? Refractive index of water is 1.33. (Consider the bulb to be a point source.)

Options

A. `sqrt(400)ms^(-1)`
B. `sqrt(600)ms^(-1)`
C. `sqrt(60)ms^(-1)`
D. None of these

Answer

a

Explanation

Total pressure at bottom of tank = atm . Pressure + pressure of column of water having height h
`P=P_(o)+P`
`thereforeP.=P-P_(o)=3-1`
`hrhog=2atm=2xx10^(5)Nm^(-2)`
`thereforeh=(2xx10^(5))/(rhog)=(2xx10^(5))thereforeh=20m`
`thereforev=sqrt(2gh)=sqrt(2xx10xx20)=sqrt(400)ms^(-1)`