If the intensity is increased by a factor of $20$,then how many decibels in the sound level increased?

$A$ ray of light of intensity $I$ is incident on a parallel glass slab at point $A$ as shown in the diagram. It undergoes partial reflection and refraction. At each reflection, $25\%$ of incident energy is reflected. The rays $AB$ and $A'B'$ undergo interference. The ratio of $I_{max}$ and $I_{min}$ is (in $: 1$)

If $\cos (A-B)=3/5$ and $\tan A \tan B=2$,then which one of the following is true?

In which reaction is a racemic mixture not obtained?

$A$ scion is grafted to a stock. The quality of fruits produced will be determined by the genotype of

When radiation of the wavelength $\lambda$ is incident on a metallic surface,the stopping potential is $4.8 \ V$. If the same surface is illuminated with radiation of double the wavelength,then the stopping potential becomes $1.6 \ V$. Then,the threshold wavelength for the surface is: