$A$ source emits light of wavelengths $4700 \ \mathring{A}$,$5400 \ \mathring{A}$,and $6500 \ \mathring{A}$. The light passes through red glass before being tested by a spectrometer. Which wavelength is seen in the spectrum?

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?

What is the frequency of the light emitted from a sodium lamp?

$A$ 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:

The maximum illumination on a screen at a distance of $2\, m$ from a lamp is $25\, lux.$ The value of total luminous flux emitted by the lamp is

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