A sensitive magnetic instrument can be shielded very effectively from outside magnetic fields by placing it inside a box of
1. Teak wood
2. Plastic material
3. Soft iron of high permeability
4. A metal of high conductivity

The variation of the intensity of magnetisation (I) with respect to the magnetising field (H) in a diamagnetic substance is described by the graph

1. OD                            2. OC

3. OB                            4. OA

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 :

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

Which of the following is not dimensionless?
(where symbols stand for their usual meanings in magnetism)
1. \(\frac{I}{H}\)
2. \(\frac{B}{\mu_0H}\)
3. \(\mu_r\)
4. \(\frac{\mu_r B}{H}\)

The unit of intensity of the magnetising field is :

1.$\frac{N}{Wb}$

2. $\frac{J}{m^3\times tesla}$

3. $\frac{J}{m\times Wb}$

4. All of these