Two identical metal plates are given charges $q_1$ and $q_2\left(q_2 < q_1\right)$ respectively. If they are now brought close together to form a parallel plate capacitor with capacitance ' C ', the potential difference ' $V$ ' between the plates is

In hydrogen atom in its ground state, the first Bohr orbit has radius ' $\mathrm{r}_1$ '. When the atom is raised to one of its excited states, the electrons orbital velocity becomes one-third. The radius of that orbit is

Heat supplied $d Q=$ increased in internal energy dU is true for

With a resistance ' X ' connected in series with a galvanometer of resistance $100 \Omega$, it acts as a voltmeter of range $0-15 \mathrm{~V}$. To double the range, a resistance of $1500 \Omega$ is to be connected in series with ' X '. The value of ' X ' in ohm is