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?

$A$ laser beam is used for surgery because it can be...

Mention the colours which have the least and the most wavelength in visible light.

The intensity of light from a continuously emitting laser source operating at $638 \,nm$ wavelength is modulated at $1 \,GHz$. The modulation is done by momentarily cutting the intensity off with a frequency of $1 \,GHz$. What is the farthest distance apart two detectors can be placed in the line of the laser light,so that they can see the portions of the same pulse simultaneously?
(Consider the speed of light in air $c = 3 \times 10^{8} \,m/s$)

In the given figure,light of intensity $I$ is incident on a glass slab at point $A$ at an angle of incidence $\theta_1$. It undergoes partial reflection and partial refraction. At each reflection,$25\%$ of the incident energy is reflected. If interference occurs between the rays $AB$ and $A'B'$,then $I_{max}/I_{min} = \dots$ (in $: 1$)

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?