Magnetism & Matter - 5th Jan 2021Contact Number: 9667591930 / 8527521718

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If a magnet is suspended at angle $30\xb0$ to the magnetic meridian, the dip needle makes an angle of $45\xb0$ with the horizontal. The value of real dip angle at the place is

1. ${\mathrm{tan}}^{-1}\frac{\sqrt{3}}{2}$

2. ${\mathrm{tan}}^{-1}1$

3. ${\mathrm{tan}}^{-1}\frac{1}{2}$

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

Time period for a magnet is *T*. If it is divided in four equal parts along its axis and perpendicular to its axis as shown then time period for each part will be

1. 4T

2. T/4

3. T/2

4. T

Two equal bar magnets are kept as shown in the figure. The direction of the resultant magnetic field, indicated by arrowhead at the point *P* is: (approximately)** **

1. | 2. | ||

3. | 4. |

The relative permeability $\left({\mu}_{r}\right)$ of a ferromagnetic substance varies with temperature *(T)* according to the curve:

1. *A*

2. *B*

3. *C*

4. *D*

The magnetic field due to a short magnet at a point on its axis at a distance X cm from the middle point of the magnet is 200 Gauss. The magnetic field at a point on the neutral axis at a distance of X cm from the middle of the magnet is:

1. 100 Gauss

2. 400 Gauss

3. 50 Gauss

4. 200 Gauss

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. |

A long solenoid has 1500 turns per metre and an iron core of ${\mu}_{r}$ = 1100 is kept inside it. 2A current flows in the coil of the solenoid. If the core is heated beyond curie temperature, then:

1. | The H and B fields in the solenoid reduce to zero. |

2. | The H and B fields in the solenoid remain unchanged. |

3. | The H field in the solenoid is nearly unchanged but B field decreases significantly. |

4. | The B field in the solenoid is nearly unchanged but the H field decreases significantly. |

A ferromagnetic material is placed in an external magnetic field. The magnetic domains:

1. | must increase in size. |

2. | must decrease in size. |

3. | may increase or decrease in size. |

4. | disappear. |

The magnetic moment of a magnet \((10 ~cm\times 4~cm\times1~cm)\) is \(4 ~Am^2\). Its intensity of magnetisation is:

1. 10^{3 }A/m

2. 10^{2 }A/m

3. 10^{5 }A/m

4. 10^{4 }A/m

If a magnetic dipole of dipole moment $\mu $ is rotated through an angle $\theta $ with respect to the direction of the magnetic field B, then work done is :

1. $\mu $Bsin$\theta $

2. $\mu $B(1-sin$\theta $)

3. $\mu $Bcos$\theta $

4. $\mu $B(1-cos$\theta $)

The magnetic dip at two perpendicular positions of a dip circle is 45$\xb0$ and 30$\xb0$. The true dip at that place is :

$1.{\mathrm{cot}}^{-1}\left(\sqrt{2}\right)$

$2.{\mathrm{cot}}^{-1}\left(2\right)$

$3.{\mathrm{cot}}^{-1}\left(\frac{1}{\sqrt{2}}\right)$

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

The magnetic susceptibility $\chi $ of a diamagnetic material depends on absolute temperature T as:

$1.$ $\chi $ $\propto $ $$ $T$ $$

$2.$ $\chi $ $\propto $ $\frac{1}{T}$

$3.$ $\chi $ $\propto $ $$ ${T}^{0}$ $$

$4.$ $\chi $ $\propto $ $\frac{1}{\sqrt{T}}$

The material which is used to make permanent magnet has:

1. | High retentivity, low coercivity |

2. | Low retentivity, low coercivity |

3. | Low retentivity, high coercivity |

4. | High retentivity, high coercivity |

The bar magnet \(A\) of magnetic moment \(M_A\) is found to oscillate at a frequency twice that of magnet \(B\) of magnetic moment \(M_B\) and the same moment of inertia when placed in a vibration magnetometer. We may say that:

1. \(M_B=8M_A\)

2. \(M_A= 4M_B\)

3. \(M_A=8M_B\)

4. \(M_A=2M_B\)

A small bar magnet is placed with its north pole facing the magnetic north pole. The neutral points are located at a distance r from its centre. If the magnet is rotated by 180^{o}, the neutral point shall be obtained at a distance of:

1. \(2r\)

2. \(\sqrt{2}r\)

3. \(2^{\frac{1}{3}}r\)

4. \(\frac{r}{2\sqrt{2}}\)

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