A hydrogen atom absorbs energy and rises to $n=3$ state from its ground state $n=1$. If the potential energy of the atom at its ground state is -13.6 eV , find the wave length emitted by it when it returns to its ground state:
{Planck's constant $=6.6 \times 10^{34} \mathrm{~J} \mathrm{~s}$ }
$12000^{\circ} \mathrm{A}$
$1020^{\circ} \mathrm{A}$
$7000^{\circ} \mathrm{A}$
$4000^{\circ} \mathrm{A}$
On both sides of a magnetic needle, two short magnets A and B are placed on the same horizontal line which is perpendicular to the magnetic meridian. The south poles of $A$ and $B$ are facing each other, which are 10 cm and 20 cm respectively from the magnetic needle. If the needle remains undeflected, the ratio of the magnetic moment of $A$ to that $B$ is:
$2:1$
$8:1$
$1: 8$
$1: 2$
A parallel combination of ' $n$ ' cells of emf ' $E$ ' and internal resistance ' $r$ ' each, are connected across the external resistance ' $R$ '. If the external resistance ' $R$ ' is negligibly small, then the current ' $I$ ' through the external resistance is:
$I=\frac{E}{n R}$
$I=\frac{E}{R}$
$I=\frac{n E}{R}$
$I=\frac{r E}{n}$
A particle moves along a parabolic path $y=9 x^2$ in such a way that the x component of velocity remains constant. If, the acceleration of the particle is $2 j m s^{-2}$, find the x component of velocity.
$\frac{1}{9} m s^{-1}$
$\frac{1}{4} m s^{-1}$
$\frac{1}{3} m s^{-1}$
$\frac{1}{6} m s^{-1}$
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