A magnetic needle is made to vibrate in uniform field H, then its time period is T. If it vibrates in the field of intensity 4H, its time period will be

(a) 2T                             (b) T/2

(c) 2/T                            (d) T

Concept Questions :-

Earth's magnetism
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Difficulty Level:

A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30o and 15 oscillations per minute at a place where dip angle is 60o. The ratio of total earth's magnetic field at the two places is

1. $3\sqrt{3}:8$                      2. $16:9\sqrt{3}$

3. 4:9                           4. $2\sqrt{3}:9$

Concept Questions :-

Analogy between electrostatics and magnetostatics
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Difficulty Level:

A bar magnet A of magnetic moment MA is found to oscillate at a frequency twice that of magnet B having identical size as magnet A, of magnetic moment MB when placed in a vibrating magneto-meter. We may say that

(a) ${M}_{A}=2{M}_{B}$                  (b) MA = 8MB

(c) MA = 4MB                  (d) MB = 8MA

Concept Questions :-

Bar magnet
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Difficulty Level:

A magnet of magnetic moment M oscillating freely in earth's horizontal magnetic field makes n oscillations per minute. If the magnetic moment is quadrupled and the earth's field is doubled, the number of oscillations made per minute would be

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

3. $2\sqrt{2}n$                        4. $\sqrt{2}n$

Concept Questions :-

Bar magnet
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Difficulty Level:

Magnets A and B are geometrically similar but the magnetic moment of A is twice that of B. If T1 and T2 be the time periods of the oscillation when their like poles and unlike poles are kept together respectively, then $\frac{{T}_{1}}{{T}_{2}}$ will be

(a) 1/3                              (b) 1/2

(c) $1}{\sqrt{3}}$                          (d) $\sqrt{3}$

Concept Questions :-

Bar magnet
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Difficulty Level:

The number of turns and radius of cross-section of the coil of a tangent galvanometer is doubled. The reduction factor K will be
1. K                              2. 2K
3. 4K                            4. K/4

Concept Questions :-

Moving coil galvanometer
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Difficulty Level:

A magnetic needle suspended by a silk thread is vibrating in the earth's magnetic field. If the temperature of the needle is increased by 500°C, then

(a) The time period decreases

(b) The time period remains unchanged

(c) The time period increases

(d) The needle stops vibrating

Concept Questions :-

Bar magnet
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Difficulty Level:

Two tangent galvanometers having coils of the same radius are connected in series. A current flowing in them produces deflections of 60° and 45° respectively. The ratio of the number of turns in the coils is

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

3. $\frac{\sqrt{3}+1}{\sqrt{3}-1}$          4. $\frac{\sqrt{3}}{1}$

Concept Questions :-

Moving coil galvanometer
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Difficulty Level:

The time period of oscillation of a bar magnet suspended horizontally along the magnetic meridian is T0. If this magnet is replaced by another magnet of the same size and pole strength but with double the mass, the new time period will be

(a) $\frac{{T}_{0}}{2}$                            (b) $\frac{{T}_{0}}{\sqrt{2}}$

(c) $\sqrt{2}{T}_{0}$                         (d) 2T0

Concept Questions :-

Bar magnet
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Difficulty Level:

The magnet of a vibration magnetometer is heated so as to reduce its magnetic moment by 19%. By doing this the periodic time of the magnetometer will

1. Increase by 19%       2. Decrease by 19%

3. Increase by 11%       4. Decrease by 21%

Concept Questions :-

Bar magnet