$A$ screen receives $3 \ W$ of radiant flux of wavelength $6000 \ \mathring{A}.$ One lumen is equivalent to $1.5 \times 10^{-3} \ W$ of monochromatic light of wavelength $5550 \ \mathring{A}.$ If the relative luminosity for $6000 \ \mathring{A}$ is $0.685$ while that for $5550 \ \mathring{A}$ is $1.00,$ then the luminous flux of the source is:

Red light differs from blue light in its

In interference and diffraction,the light energy is redistributed. If it reduces in one region,producing a dark fringe,it increases in another region,producing a bright fringe. Statement $A$: As there is no gain or loss of energy,these phenomena are consistent with the principle of conservation of energy. Statement $B$: Diffraction and interference are characteristics exhibited only by light waves. Choose the correct answer from the options given below:

$A$ circular disc of which $2/3$ part is coated with yellow and $1/3$ part is with blue. It is rotated about its central axis with high velocity,then it will be seen as

$A$ monochromatic light source of wavelength $\lambda$ is placed at $S$. Three slits $S_1, S_2$ and $S_3$ are equidistant from the source $S$ and the point $P$ on the screen. $S_1P - S_2P = \lambda / 6$ and $S_1P - S_3P = 2\lambda / 3$. If $I$ is the intensity at $P$ when only one slit is open,the intensity at $P$ when all the three slits are open is

Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of $60^o$,by what fraction will the illuminance change?