A moving coil galvanometer has $N$ number of turns in a coil of effective area $A$, it carries a current $I$. The magnetic field $B$ is radial. The torque acting on the coil is
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An infinitely long conductor $PQR$ is bent to form a right angle as shown. A current $I$ flows through $PQR$ The magnetic field due to this current at the point $M $ is $H_1$. Now another infinitely long straight conductor $QS$ is connected at $Q$ so that the current is $I/2$ in $QR$ as well as in $QS$, The current in $PQ$ remaining unchanged. The magnetic field at $M$ is now ${H_{2.}}$The ratio ${H_1}/{H_2}$ is given by
A current loop $ABCD$ is held fixed on the plane of the paper as shown in the figure. The arcs $ BC$ (radius $= b$) and $DA $ (radius $= a$) of the loop are joined by two straight wires $AB $ and $CD$. A steady current $I$ is flowing in the loop. Angle made by $AB$ and $CD$ at the origin $O$ is $30^o $. Another straight thin wire with steady current $I_1$ flowing out of the plane of the paper is kept at the origin.
The magnitude of the magnetic field $(B)$ due to the loop $ABCD$ at the origin $(O)$ is :
A galvanometer having a resistance of $20\,\Omega $ and $30\, divisions$ on both sides has figure of merit $0.005\, ampere /division$. The resistance that should be connected in series such that it can be used as a voltmeter upto $15\, volt$ is ........... $\Omega$
A hairpin like shape as shown in figure is made by bending a long current carrying wire. What is the magnitude of a magnetic field at point $P$ which lies on the centre of the semicircle ?
Due to the flow of current in a circular loop of radius $R$, the magnetic field produced at the centre of the loop is $B$. The magnetic moment of the loop is :-
A singly ionized magnesium atom $(A=24)$ ion is accelerated to kinetic energy $5\,keV$ and is projected perpendicularly into a magnetic field $B$ of the magnitude $0.5\,T$. The radius of path formed will be___________ $cm$
$PQ$ and $RS$ are long parallel conductors separated by certain distance. $M$ is the mid-point between them (see the figure). The net magnetic field at $M$ is $B$ . Now, the current $2\,A$ is switched off. The field at $M$ now becomes