When the $N$-pole of a bar magnet points towards the geographic south and the $S$-pole points towards the geographic north,the null points are located at the:

The tangent galvanometer,when connected in series with a standard resistance,can be used as:

$A$ tangent galvanometer shows a deflection of $45^{\circ}$ when a $10 \, mA$ current passes through it. If the horizontal component of the Earth's magnetic field is $3.6 \times 10^{-5} \, T$ and the radius of the coil is $10 \, cm$,find the number of turns in the coil.

$A$ magnet makes $20$ and $15$ oscillations in $1$ minute at two places where the angles of dip are $30^{\circ}$ and $60^{\circ}$ respectively. What is the ratio of the total magnetic fields at these two places?

$A$ magnetic needle oscillates in a horizontal plane with a period $T$ at a place where the angle of dip is $60^{\circ}$. When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian,its period will be

$A$ magnetic needle is made to vibrate in a uniform magnetic field $H$. Its time period is $T$. If it vibrates in a field of intensity $4H$,its time period will be: