Initially $n$ identical capacitors are joined in parallel and are charged to potential V. Now they are separated and joined in series. Then

When the electron orbiting in hydrogen atom goes from one orbit to another orbit (principal quantum number $=n$ ), the de-Broglie wavelength ( $\lambda$ ) associated with it is related to $n$ as

A constant force acts on two different masses independently and produces accelerations $\mathrm{A}_1$ and $A_2$. When the same force acts on their combined mass, the acceleration produced is

When cell of e.m.f. ' $E_1$ ' is connected to potentiometer wire, the balancing length is ' $l_l$ '. Another cell of e.m.f. ' $E_2$ ' $\left(E_1>E_2\right)$ is connected so that two cells oppose each other, the balancing length is ' $l_1$ '. The ratio $E_1: E_2$ is