A ferromagnetic substance is placed in the varying magnetising field H. The magnetic induction B is a measure for various values of the direct and reverse magnetising field. Following graph has been plotted for B versus H. Choose the wrong statement:

1. There is a limit of direct and reverse external magnetising field at which the magnetisation and hence the magnetic induction saturates.

2. Even after removing the external magnetising field, some residual magnetisation called 'retentivity' is left over the substance.

3. On increasing the reverse magnetising field, the magnetic induction decreases to zero for a value of the magnetising field which is known as 'susceptibility'.

4. On increasing the reverse magnetising field, the magnetic induction decreases to zero for a value of magnetising field known as 'coercivity'.

A vibration magnetometer is placed at the south pole; then the time period will be:

1. zero

2. infinity

3. same as at the magnetic equator

4. same as at any other place on earth

A magnetic needle suspended by a silk thread is vibrating in the earth's magnetic field. If the temperature of the needle is increased, then:

1. The time period decreases.

2. The time period remains unchanged.

3. The time period increases.

4. The time period first decreases then increases.

What will be the energy loss per hour in the iron core of a transformer if the area of its hysteresis loop is equivalent to 2500 erg/cm³. The frequency of the alternating current is 50 Hz. The mass of the core is 10 kg and the density of iron is 7.5 gm/cm³ :

$1. 2\times {10}^2 \mathrm{Joule}$
$2. 4\times {10}^3 \mathrm{Joule}$
$3. 6\times {10}^4 \mathrm{Joule}$
$4. 8\times {10}^5 \mathrm{Joule}$

The correct relation between magnetic susceptibility and relative permeability is:

$1. \mathrm{\chi }={\mathrm{\mu }}_{\mathrm{r}}-1$
$2. \mathrm{\chi }={\mathrm{\mu }}_{\mathrm{r}}+1$
$3. \mathrm{\chi }=1-{\mathrm{\mu }}_{\mathrm{r}}$
$4. \mathrm{\chi }={\mathrm{\mu }}_{\mathrm{r}}$

At any place on earth, the horizontal component of earth's magnetic field is $\sqrt{3}$ times the vertical component. The angle of dip at that place will be:

1. 60°

2. 45°

3. 90°

4. 30°

Magnetic susceptibility of the given paramagnetic substance at room temperature is:

1. 2.8 × 10^–3

2. 57

3. 0.19

4. 0.57

In the given diagram, substance A(Zn) and substance B(Mn) are placed at the ends of a long current-carrying solenoid, then:

1. A will move away from the center C and B will move towards the center C.

2. A will move towards C and B will move away from the center C.

3. Both will move away from the center C.

4. Both will move towards the center C.

A short bar magnet is placed with its north pole pointing north. The neutral point is 10 cm away from the centre of the magnet. If ${\mathrm{B}}_{\mathrm{H}}$=0.4 G, calculate the magnetic moment of the magnet.

1. 0.06 A-${\mathrm{m}}^2$

2. 0.4 A${\mathrm{m}}^2$

3. 0.8 A-${\mathrm{m}}^2$

4. None of these

The magnitude of the earth's magnetic field at a place is ${\mathrm{B}}_{\mathrm{o}}$ and the angle of dip is $\mathrm{\delta }$. A horizontal conductor of length l, lying north-south, moves eastwards with a velocity v. The emf induced across the conductor is:

1. Zero

2. ${\mathrm{B}}_{\mathrm{o}}$lv

3. ${\mathrm{B}}_{\mathrm{o}}$lvsin$\mathrm{\delta }$

4.  ${\mathrm{B}}_{\mathrm{o}}$lvcos$\mathrm{\delta }$