Magnetic Declination

Q. 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 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. $2^{\frac{1}{4}}$
2. $2$
3. $2^{\frac{3}{4}}$
4. $2^{\frac{1}{2}}$

Q.

For a uniform rectangular sheet shown in the figure, the ratio of moments of inertia about the axes perpendicular to the sheet and passing through $O$ (the centre of mass) and $O$ (corner point) is:

1. $\frac{1}{2}$

2. $\frac{2}{3}$

3. $\frac{1}{4}$

4. $\frac{1}{8}$

Q.

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 $\theta$. Then $\left(\frac{\tan \theta }{\tan \theta }\right)$ is

1. $\frac{1}{\cos x}$

2. $\frac{1}{\sin x}$

3. $\frac{1}{\tan x}$

4. $\cos x$

Q. 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 $2^{\frac{5}{4}}$ 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. $2^{\frac{1}{4}}$
2. $2^{\frac{1}{2}}$
3. $2$
4. $2^{\frac{3}{4}}$

Q. A wire carrying current $I$ is laid in shape of a curve which is represented in plane polar coordinate system as,
$r=b+\frac{c}{\pi }\theta for0\le \theta \le \frac{\pi }{2}$
Here $b$ and $c$ are positive constants. $\theta$ is the angle measured with respect to positive $X$ direction in anticlockwise sense and $r$ is the distance from origin (see figure). The magnetic field at the origin due to the wire is found to be $\frac{{\mu }_{o}I}{xc}ln(1+\frac{c}{yb})$
The value of xy is

Q.

Declination is the angle between:

1. horizontal and vertical components of earth’s magnetic field

2. geographic and magnetic meridian

3. horizontal component and total magnetic field of the earth

4. geographic meridian and horizontal component of earth's magnetic field

Q. A vertical rod of length l is now moving with a constant velocity v towards east. the vertical component of Earths magnetic field is B and angle of dip is theta . The induced EMF in the rod is : Blv sin theta Blv cos theta Blv cot theta Blv tan theta

Q. Define angle of inclination (magnetic declination).
In the magnetic meridian of a certain place, the horizontal component of earth's magnetic field is $0.25$ gauss and the dip angle is ${60}^o$. At this place find the value of earth's magnetic field.

Q. The time period of a freely suspended magnet is $2sec$. If it is broken in length into two equal parts and one part is suspended in the same way, then its time period (in seconds) will be

Q. Why is the angle of declination greater at places located near the poles as compared to that of places located near the equator?

Q. The magnetic compass is not useful for navigation near the magnetic poles because -

1. The magnetic field near the poles is zero.
2. The magnetic field near the poles is almost vertical.
3. At low temperature, the compass needle looses its magnetic properties.
4. None of these

Q. A short bar magnet of magnetic moment $5.25\times {10}^{-2}J{T}^{-1}$ is placed with its axis perpendicular to the earths field direction. At what distance from the centre of the magnet, the resultant field is inclined at ${45}^{\circ }$ with earths field on
(a) its normal bisector and (b) its axis. Magnitude of the earths field at the place is given to be $0.42G$. Ignore the length of the magnet in comparison to the distances involved

Q. Define magnetic declination.

Q. Time period of qscillations of a magnet of magnetic moment M and moment of inertia I in a vertical plane perpendicular to the magnetic meridan at a place where earth's horizontal and vertical component of mgnetic field are $B_{H}and{B}_V$ respectively is

1. $T=2\pi {\sqrt{\frac{I}{M(B_v^2+B_H^2)}}}^{1/2}$
2. $T=2\pi \sqrt{\frac{I}{M{B}_v}}$
3. $T=2\pi \sqrt{\frac{I}{M{B}_H}}$
4. NONE

Q. A magnet is cut in three equal parts by cutting it perpendicular to its length. The time period of original magnet is T${}_0$ in a uniform magnetic field B. Then, the time period of each part in the same magnetic field is

1. $\frac{T_0}{4}$
2. None of these
3. $\frac{T_0}{2}$
4. $\frac{T_0}{3}$

Q. At a certain place, the horizontal component $B_0$ and the vertical component $V_0$ of the earth's magnetic field are equal in magnitude. the total intensity at the place will be

1. $B_0$
2. $2B_0$
3. $B_0^2$
4. $\sqrt{2}{B}_0$

Q. A ship has to reach a place which is due west from its present position. Declination at this point is ${15}^0$. The direction from compass needle in which it should sail is :

1. ${75}^0$
2. ${15}^0$
3. ${105}^0$
4. ${165}^0$

Q.

A line joining places of equal horizontal field is called

1. aclinic
2. isodynamic
3. isoclinic
4. isogonal

Q. At a place on the surface of earth vertical component of earths field is two times that of horizontal component. Then the latitude angle at the place is

1. ${45}^o$
2. ${\tan }^{-1}\left(1/2\right)$
3. ${\tan }^{-1}\left(2\right)$
4. $0^o$

Q. A telephone cable at a place has four long straight horizontal wires carrying a current of $1.0$A in the same direction east to west. The earth's magnetic field at the place is $0.39$G, and the angle of dip is ${35}^0$. The magnetic declination is nearly zero. What are the resultant magnetic fields at point $4.0$ cm below the cable?

1. $0.50$ G
2. $0.000025$ G
3. $1.25$ G
4. $2.50$ G

Q. At a place on the surface of earth vertical component of earth's field is two times that of horizontal component. Then the latitude angle at that place is

1. ${\tan }^{-1}\left(2\right)$
2. ${\tan }^{-1}\left(1/2\right)$
3. ${45}^o$
4. $0^o$

Q. Angle of declination at a place is 18 degree how can a magnetic compass be used to find the exact direction of geographical North at that place

Q. Name three elements of the earth's magnetic field which help in defining earth's magnetic field completely.

Q. Assure me that the angle between magnetic meridian and geomertical meridian is 20.5 degree.

Q. A vertical rod of length l is moved with constant velocity v towards east. The vertical component of earth magnetic field is B and angle of dip is θ. The induced e.m.f. in the rod is
(1) Blv sin θ (2) Blv tan θ (3) Blv cot θ (4) Blv cos θ

Q. A thin rectangular magnet suspended freely has a period of oscillation equal to T. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freetly in the same field. If its period of oscillation is T', then ratio $\frac{T^{\prime }}{T}$ is

1. $\frac{1}{4}$
2. 2
3. $\frac{1}{2\sqrt{2}}$
4. $\frac{1}{2}$

Q. The current in the coil is reversed, and the coil is rotated about its vertical axis by an angle of ${90}^o$ in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the places to be zero.

Q.

define magnetic declination

Q.

A line joining places of same declination is called

1. agonic
2. isoclinic
3. isodynamic
4. isogonal

Q. What is magnetic declination?