In a movie hall,the distance between the projector and the screen is increased by $1\%$. The illumination on the screen is:

Define a ray and a beam of light.

Four bulbs,red,green,white and blue (denoted by $R, G, W$ and $B$ respectively) are kept in front of a converging lens (as shown in the figure). The observer sees that the green and blue bulbs are kept to the left of the principal axis,while the red and white bulbs are kept to the right of the principal axis. He also sees that the red and green bulbs are above the principal axis,while the white and blue bulbs are below the principal axis. The screens $S_1$ and $S_2$ are set at appropriate positions for focusing to view the images. Choose the figure that correctly represents the images as seen by the observer.

$A$ ray of light moving along the vector $\vec{v} = -\hat{i} - 2\hat{j}$ undergoes refraction at an interface of two media,which is the $x-z$ plane. The refractive index for $y > 0$ is $\mu_1 = 2$,while for $y < 0$,it is $\mu_2 = \sqrt{5}/2$. Find the unit vector along which the refracted ray moves.

$A$ small piece of wire bent into an $L$ shape with upright and horizontal portions of equal lengths,is placed with the horizontal portion along the axis of a concave mirror whose radius of curvature is $10 \, cm$. If the bend is $20 \, cm$ from the pole of the mirror,then the ratio of the lengths of the images of the upright and horizontal portions of the wire is:

The flat bottom of a cylindrical tank is silvered and water $(\mu = 4/3)$ is filled in the tank up to a height $h$. $A$ small bird is hovering at a height $3h$ from the bottom of the tank. When a small hole is opened near the bottom of the tank,the water level falls at the rate of $1\, cm/s$. The bird will perceive that its image's velocity is: