A bird is flying 3m above the surface of water. To a fish underwater, the height of the bird from the water surface appears to be $\left[\mathrm{Take} {\mathrm{\mu }}_{\mathrm{w}}=4/3\right]$

1.  2 m

2.  3.33 m

3.  4 m

4.  (4/3) m

If the focal length of the objective lens is increased then the magnifying power of:

A unit vector along incident ray of lights is $\hat{\mathrm{i}}$. The unit vector for the corresponding refracted ray of lights is $\hat{\mathrm{r}}$. $\hat{\mathrm{n}}$ is a unit vector normal to the boundary of the medium and directed towards the incident medium. If m be the refractive index of the medium, then Snell's law (2nd) of refraction is 

1. $\hat{\mathrm{i}}\times \hat{\mathrm{n}}=\mathrm{\mu }\left(\hat{\mathrm{n}}+\overrightarrow{\mathrm{r}}\right)$

2. $\hat{\mathrm{i}}.\hat{\mathrm{n}}=\mathrm{\mu }\left(\hat{\mathrm{n}}.\hat{\mathrm{r}}\right)$

3. $\hat{\mathrm{i}}\times \hat{\mathrm{n}}=\mathrm{\mu }\left(\hat{r}\times \hat{\mathrm{n}}\right)$

4. $\mathrm{\mu }\left(\hat{\mathrm{i}}\times \hat{\mathrm{n}}\right)=\hat{\mathrm{r}}\times \hat{\mathrm{n}}$

An air bubble in glass slab ($\mu$ = 1.5) when viewed from one side appears to be at 6 cm and from opposite side 4 cm. The thickness of glass slab is

(1) 10 cm                       

(2) 6.67 cm

(3) 15 cm                       

(4) none of these

A diver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his waterproof flash light:

(1) he must direct the beam vertically upwards.

(2) he has to direct the beam horizontally.

(3) he has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence for total internal reflection.

(4) he has to direct the beam at an angle to the vertical which is slightly more than the critical angle of incidence for internal reflection.

A thin convergent glass lens ($\mu$_g = 1.5) has a power of + 5.0 D. When this lens is immersed in a liquid of refractive index $\mu$₁ it acts as a divergent lens of focal length 100 cm. The value of $\mu$₁ must be

(1) 4/3           

(2) 5/3         

(3) 2           

(4) 7/3

Convergence of concave mirror can be decreased by dipping in

(1) Water

(2) Oil

(3) Both

(4) None of these