Some currency notes (to avoid counterfeits) change their colour as you tilt them. This is due to

When petrol leaking from a vehicle falls on a rain-wet road,colours are observed. This is due to the.......... of light.

In a biprism experiment,by using light of wavelength $5000 \ \mathring{A}$,$5 \,mm$ wide fringes are obtained on a screen $1.0 \,m$ away from the coherent sources. The separation between the two coherent sources is.....$mm$.

In a Fresnel's biprism experiment,coherent sources are obtained by which of the following phenomena?

In a biprism experiment using sodium light $\lambda_1 = 6000\, \mathring{A}$,an interference pattern is obtained in which $20$ fringes occupy $2\, cm$. On replacing sodium light by another source of wavelength $\lambda_2$ without making any other change,$30$ fringes occupy $2.7\, cm$ on the screen. What is the value of $\lambda_2$ in $\mathring{A}$?

The beautiful iridescent (like a rainbow) colors on the wings of a tropical or morpho butterfly are due to