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A helium nucleus makes a full rotation in a circle of radius $0.8$ metre in two seconds. The value of the magnetic field $B$ at the centre of the circle will be
A thin flexible wire of length $\mathrm{L}$ is connected to two adjacent fixed points and carries a current $\mathrm{I}$ in the clockwise direction, as shown in the figure. When the system is put in a uniform magnetic field of strength $B$ going into the plane of the paper, the wire takes the shape of a circle. The tension in the wire is
A charge particle of $2\,\mu\,C$ accelerated by a potential difference of $100\,V$ enters a region of uniform magnetic field of magnitude $4\,m\,T$ at right angle to the direction of field. The charge particle completes semicircle of radius $3\,cm$ inside magnetic field. The mass of the charge particle is $........\times 10^{-18}\,kg$.
In a uniform magnetic field of $0.049 \mathrm{~T}$, a magnetic needle performs $20$ complete oscillations in $5$ seconds as shown. The moment of inertia of the needle is $9.8 \times 10^{-5} \mathrm{~kg} \mathrm{~m}^2$. If the magnitude of magnetic moment of the needle is $x \times 10^{-5} \mathrm{Am}^2$, then the value of ' $x$ ' is :
A particle of charge $ - 16 \times {10^{ - 18}}$ $coulomb$ moving with velocity $10\,\,m{s^{ - 1}}$ along the $x$-axis enters a region where a magnetic field of induction $B$ is along the $y$-axis, and an electric field of magnitude ${10^4}\,\,V/m$ is along the negative $z$-axis. If the charged particle continues moving along the $x$-axis, the magnitude of $B$ is
A horizontal metallic rod of mass $'m'$ and length $'l'$ is supported by two vertical identical springs of spring of spring constant $'K'$ each and natural length $l_0.$ A current $'i'$ is flowing in the rod in the direction shown. If the rod is in equilibrium then the length of each spring in this state is :-
Two very thin metallic wires placed along $X$ and $Y$-axis carry equal currents as shown here. $AB$ and $CD$ are lines at $45^\circ $ with the axes with origin of axes at $O$. The magnetic field will be zero on the line
A $10 \;eV$ electron is circulating in a plane at right angles to a uniform field at magnetic induction $10^{-4} \;W b / m^{2}(=1.0$ gauss), the orbital radius of electron is ........ $cm$