An electric bulb illuminates a plane surface. The intensity of illumination on the surface at a point $2 \ m$ away from the bulb is $5 \times 10^{-4} \ phot$ $(lumen/cm^2)$. The line joining the bulb to the point makes an angle of $60^{\circ}$ with the normal to the surface. The intensity of the bulb in candela is

$Lux$ is equal to:

$A$ film projector magnifies a $100 \; cm^2$ film strip on a screen. If the linear magnification is $4$,the area of the magnified film on the screen is.....$cm^2$.

The camera lens has an aperture of $f$ and the exposure time is $(1/60) \, s$. What will be the new exposure time if the aperture becomes $1.4 \, f$?

$A$ concave mirror has a radius of curvature of $40\, cm$. It is at the bottom of a glass that has water filled up to $5\, cm$ (see figure). If a small particle is floating on the surface of water,its image as seen from directly above the glass is at a distance $d$ from the surface of water. The value of $d$ is close to ......$cm$ (Refractive index of water $= 1.33$)

In the figure shown,consider the first reflection at the plane mirror and the second at the convex mirror. $AB$ is the object.