An oscillator is nothing but an amplifier with

$\mathop {\lim}\limits_{x \to 0} \frac{{\sin \left( {\pi {{\cos }^2}x} \right)}}{{{x^2}}} = $

If the wavelength of an electromagnetic radiation is $2000 \ \mathring{A}$,what is its energy in ergs?

Two finite sets have $m$ and $n$ elements. The total number of subsets of the first set is $56$ more than the total number of subsets of the second set. The values of $m$ and $n$ are

Which of the following statements does not form part of Bohr's model of the hydrogen atom?

The products formed in the reaction of phenol with $Br_2$ dissolved in $CS_2$ at $0^{\circ} C$ are