A charge of $5 \mu \mathrm{C}$ is placed at the centre of a spherical shell $S_1$ of radius 10 cm . Now this system is enclosed inside another spherical shell $S_2$ of radius 20 cm . The ratio of the electrical flux through the surface $S_2$ to $S_1$ is :
$1: 2$
$4:1$
$2:1$
$1: 1$
The main function of cadmium used in the nuclear reactor is:
It removes the heat produced at the core of the reactor
It gives energy to the secondary neutrons produced in the nuclear fission
It slows down the fast moving secondary neutrons produced during the nuclear fission
To capture the slow neutron produced in the nuclear reactor
What is the frequency of the electron in the first orbit of hydrogen atom of orbital radius $0.5 \times 10^{-10} \mathrm{~m}$, if its orbital velocity in that orbit is $2.2 \times 10^6 \mathrm{~ms}^{-1}$.
$3.49 \times 10^{15} \mathrm{~Hz}$
$3.49 \times 10^{13} \mathrm{~Hz}$
$6.98 \times 10^{15} \mathrm{~Hz}$
$6.98 \times 10^{13} \mathrm{~Hz}$
An object is dropped from a certain point A at a height ' h ' from the ground. During it's journey straight downwards, the object passes points $B$ and $C$ such that the ratio of time taken $t_1$ to cover $A B$ and $t_2$ to cover $B C$ is $1:(\sqrt{2}-1)$. What is the ratio of distances $A B: B C$ ?
$1: 1$
$(\sqrt{2}-1): 1$
$1: \sqrt{2}$
$\sqrt{2}: 1$
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