A vibration magnetometer consists of two identical bar magnets placed one over the other such that they are perpendicular and bisect each other. The time period of oscillation in a horizontal magnetic field is $2^{\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$4$}\right.}$ seconds. One of the magnets is removed and if the other magnet oscillates in the same field, then the time period in seconds is:

1. $2^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$4$}\right.}$
${\mathrm{2.\; 2}}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$
3. 2
4. $2^{\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.}$

A cylindrical rod magnet has a length of 5 cm and a diameter of 1 cm. It has a uniform magnetization of 5.30 × 10³Amp/m³. What is its magnetic dipole moment?

1. $1\times {10}^{-2} J/T$                   

2. $2.08\times {10}^{-2} J/T$

3. $3.08\times {10}^{-2} J/T$              

4. $1.52\times {10}^{-2} J/T$

Two magnets of equal mass are joined at right angles to each other as shown the magnet 1 has a magnetic moment 3 times that of magnet 2. This arrangement is pivoted so that it is free to rotate in the horizontal plane. In equilibrium what angle will the magnet 1 subtend with the magnetic meridian

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

2. ${\tan }^{-1}\left(\frac{1}{3}\right)$

3. ${\tan }^{-1}\left(1\right)$

4. $0°$

Two magnets A and B are identical and these are arranged as shown in the figure. Their length is negligible in comparison to the separation between them. A magnetic needle is placed between the magnets at point P which gets deflected through an angle $\theta$ under the influence of magnets. The ratio of distance d₁ and d₂ will be:
   
1. $(2\tan \theta {)}^{1/3}$

2. $(2\tan \theta {)}^{-1/3}$

3. $(2cot\theta {)}^{1/3}$

4. $(2cot\theta {)}^{-1/3}$

Two identical bar magnets with a length of 10 cm and weight 50 gm-weight are arranged

freely with their like poles facing in an inverted vertical glass tube. The upper magnet

hangs in the air above the lower one so that the distance between the nearest pole of the

magnet is 3mm. Pole strength of the poles of each magnet will be:

1. 6.64 amp$\times$m

2. 2 amp$\times$m

3. 10.25 amp$\times$m

4. None of these

Each atom of an iron bar$$ (5 cm × 1 cm × 1 cm) has a magnetic moment $1.8\times {10}^{-23} A{m}^2$. Knowing that the density of iron is $7.78\times {10}^3 kg{m}^{-3}$ atomic weight is 56 and Avogadro's  number is $6.02\times {10}^{23}$the magnetic moment of the bar in the state of magnetic saturation will be:

1. 4.75 Am²                 

2. 5.74 Am²

3. 7.54 Am²                 

4. 75.4 Am²

A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds. The same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds. Then the angle of dip is

1. 0^o                             2. 30^o

3. 45^o                           4. 90^o

A dip needle lies initially in the magnetic meridian when it shows an angle of dip $\theta$ at a place. The dip circle is rotated through an angle x in the horizontal plane and then it shows an angle of dip $\theta \text{'}$. Then $\frac{\tan \theta \text{'}}{\tan \theta }$ is

1. 1/cos x

2. 1/sin x

3. 1/tan x

4. cos x

A bar magnet has coercivity $4\times {10}^3 A{m}^{-1}$. It is desired to demagnetize it by inserting it inside a solenoid 12 cm long and having 60 turns. The current that should be sent through the solenoid is

1. 2 A                            2. 4 A

3. 6 A                            4. 8 A

For substances hysteresis (B - H) curves are given as shown in figure. For making temporary magnet which of the following is best?

1.		2.
3.		4.