$A$ carrot looks orange in colour because of the $\beta$-carotene molecule in it. This means that the $\beta$-carotene molecule absorbs light of wavelengths

The difference in the number of wavelengths,when yellow light propagates through air and vacuum columns of the same thickness,is one. Find the thickness of the air column. Given: Refractive index of air $\mu_a = 1.0003$,Wavelength of yellow light in vacuum $\lambda_0 = 6000 \text{ Å}$.

The figure shows $P$ and $Q$ as two equally intense coherent sources emitting radiations of wavelength $20 \, m$. The separation $PQ$ is $5.0 \, m$ and the phase of $P$ is ahead of the phase of $Q$ by $90^{\circ}$. $A, B,$ and $C$ are three distant points of observation equidistant from the mid-point of $PQ$. The intensity of radiations at $A, B,$ and $C$ will bear the ratio:

Laser is/are:

Answer the following questions:
$(a)$ When a low flying aircraft passes overhead,we sometimes notice a slight shaking of the picture on our $TV$ screen. Suggest a possible explanation.
$(b)$ As you have learnt in the text,the principle of linear superposition of wave displacement is basic to understanding intensity distributions in diffraction and interference patterns. What is the justification of this principle?

$A$ leaf which contains only green pigments is illuminated by a laser light of wavelength $0.6328 \,\mu m$. It would appear to be