Physical processes are sometimes described visually by lines. Only the following can cross.

Two light sources with equal luminous intensity are placed at a distance of $1.2\, m$ from each other. Where should a screen be placed between them such that the illuminance on one of its faces is four times that on the other face?

What is an image?

For a concave mirror, if a virtual image is formed, the graph between $m$ and $u$ is of the form:

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

For a concave mirror,if a real image is formed,the graph between $\frac{1}{u}$ and $\frac{1}{v}$ is of the form: