' $P$ ' and ' $Q$ ' are fixed points in same plane and mass ' $m$ ' is tied by string as shown in figure. If the mass is displaced slightly out of this plane and released, it will oscillate with time period $(\mathrm{PQ}=2 \mathrm{~d}, \mathrm{PR}=\mathrm{QR}=\mathrm{L})(\mathrm{g}=$ gravitational acceleration)

The instantaneous value of current in an a.c. circuit is $I=3 \sin \left(50 \pi t+\frac{\pi}{4}\right) \mathrm{A}$. The current will be maximum for the first time at

The fundamental frequency of a closed pipe of length $L$ is equal to the second overtone of a pipe open at both the ends of length (XL). The value of X is (Neglect end correction)

In the case of constant ' $\alpha$ ' and ' $\beta$ ' of a transistor ( $\alpha$ and $\beta$ are current ratios)