A ruby laser produces of wavelengths, $662.6 \mathrm{nm}$ in pulse whose duration are ${10}^{-9} \mathrm{s}.$ If the laser produces $0.39 \mathrm{J}$ of energy per pulse, how many photons are produced in each pulse?

Name the thing with the help of which we get light. Fill in the blank and find out. 

 C _ n d l e

The complete word is _____.

Fill in the blank with an appropriate word:

_____ (Oil lamp/Electric bulb) is the thing with the help of which fire gives us light.

Write ‘A’ for artificial sources of light and ‘B’ for natural sources of light.

Name the following.

This gas is used in the glowing signboard.