In the Young's double slit experiment, the intensity at a point on the screen, where the path difference is $\lambda(\lambda=$ wavelength $)$ is $\beta$. The intensity at a point where the path difference is $\lambda / 3$, will be $\left.\cos \frac{\pi}{3}=1 / 2\right]$

The P-V diagrams for particular gas of different thermodynamic processes are given by

A musical instrument ' $P$ ' produces sound waves of frequency ' $n$ ' and amplitude ' $A$ '. Another musical instrument ' $Q$ ' produces sound waves of frequency $\frac{\mathrm{n}}{4}$. The waves produced by ' $P$ ' and ' $Q$ ' have equal energies. If the amplitude of waves produced by ' $P$ ' is ' $A_P$ ', the amplitude of waves produced by ' $Q$ ' will be

Concave and convex lenses are placed touching each other. The ratio of magnitudes of their power is $2: 3$. The focal length of the system is 30 cm . The focal lengths of individual lens are