A transistor having $\alpha=0.8$ is connected in common emitter configuration. When the base current changes by 6 mA , then the change in collector current is

A uniform metal wire has length $L$, mass $M$ and density $\rho$. It is under tension $T$ and $v$ is the speed of transverse wave along the wire. The area of cross-section of the wire is

An object is clearly seen through an astronomical telescope of length 50 cm . The focal lengths of its objective and eye-piece respectively, can be

A bob of a simple pendulum has mass $m$ and is oscillating with an amplitude $a$. If the length of the pendulum is $L$, then the maximum tension in the string is $\left[\cos 0^{\circ}=1\right.$, $g=$ acceleration due to gravity]