Name some prominent scientists who have made significant contributions to the study of wave physics.

To prepare a print,the time taken is $5\, sec$ due to a lamp of $60\, W$ at a $0.25\, m$ distance. If the distance is increased to $40\, cm$,what is the time taken to prepare the similar print in seconds?

Red light differs from blue light as they have :

Statement $(S)$: Using Huygen's eye-piece,measurements can be taken but are not correct.
Reason $(R)$: The cross wires,scale,and final image are not magnified proportionately because the image of the object is magnified by two lenses,whereas the cross-wire scale is magnified by one lens only.
Identify the correct option from the following:

Fraunhofer lines are produced by the absorption of light in

$A$ 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