The force between two magnetic poles of strength unity at a separation of 1 m is:

$1.<mspace\; width="1em"></mspace>1<mspace\; width="1em"></mspace>N$
$2.<mspace\; width="1em"></mspace>\frac{{10}^{-7}}{4\mathrm{\pi }}$
$3.<mspace\; width="1em"></mspace>{10}^{-7<mspace\; width="1em"></mspace>}N$
$4.<mspace\; width="1em"></mspace>4\mathrm{\pi }<mspace\; width="1em"></mspace>\times <mspace\; width="1em"></mspace>{10}^{-7<mspace\; width="1em"></mspace>}\mathrm{m}$

The magnetic lines of force inside a bar magnet are:

The material which is used to make permanent magnet has:

On a magnetic map, the lines joining the points of the same value of the horizontal component of the earth's magnetic field are called :

1. Aclinic lines

2. Isoclinic lines

3. Isodynamic lines

4. Isogonic lines

What is the unit of pole strength of a bar magnet?

1. ampere-metre

2. ampere/metre

3. ampere/metre²

4. ampere-metre²

The ratio of magnetic length and geometrical length of a bar magnet is about :

1. 0.84

2. 0.42

3. 0.21

4. 1

An electric cable is carrying current from north to south. The position of the null point from the cable is:

1. Vertically upward

2. Vertically downward

3. Eastward

4. Nowhere

A substance is placed in an external magnetic field. If the direction of induced dipole moment is opposite to the direction of the applied magnetic field, then the substance may be

1. Paramagnetic

2. Diamagnetic

3. Ferromagnetic

4. Both (1) & (3)

If B_o is magnetic flux density in vacuum produced by a magnetising force and magnetic flux density produced by the magnetisation of a material due to the same magnetising force is B_m, then the total magnetic flux density in the material is :

$1.<mspace\; width="1em"></mspace>B_{\circ }+<mspace\; width="1em"></mspace>B_m$
$2.<mspace\; width="1em"></mspace>B_{\circ }-<mspace\; width="1em"></mspace>B_m$
$3.<mspace\; width="1em"></mspace>\frac{B_{\circ }}{B_m}$
$4.<mspace\; width="1em"></mspace>\frac{B_m}{B_{\circ }}$
$$

A magnet (primary) oscillates with frequency ${\mathrm{\nu }}_1$ in earth's magnetic field (B_H) alone. Now a secondary magnet is placed near the primary magnet. If B is the magnetic field of the second magnet on the primary magnet in the direction of B_H, the primary magnet oscillates with frequency ${\mathrm{\nu }}_2$, then the ratio of B/B_H is :

1. ${\left(\frac{{\mathrm{\nu }}_2}{{\mathrm{\nu }}_1}\right)}^2$

2. ${\left(\frac{v_2}{v_1}\right)}^2$-1

3. ${\left(\frac{{\mathrm{\nu }}_2}{{\mathrm{\nu }}_1}\right)}^2$ + 1

4. ${\left(\frac{{\mathrm{\nu }}_1}{{\mathrm{\nu }}_2}\right)}^2$-1