Neutral Point Near a Magnet, Deflection Magnetometer (JEE LEVEL)

(a)      4T             

(b)     T/4

(c)      T/2           

(d)     T

Ans (c)

3.

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 30^o and 15 oscillations per minute at a place where dip angle is 60^o. The ratio of total earth’s magnetic field at the two places is

(a)  3\sqrt{3}:8                                        

(b)  16:9\sqrt{3}

(c)  4:9    

(d)  2\sqrt{3}:9

Ans (b)

4.

Two magnets A and B are identical in mass, length and breadth but have different magnetic moments. In a vibration magnetometer, if the time period of B is twice the time period of A. The ratio of the magnetic moments {{M}_{A}}/{{M}_{B}} of the magnets will be 

(a)  1/2   

(b)  2

(c)  4        

(d)  1/4

Ans (c)

5.

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 

(a)  \frac{n}{{2\sqrt{2}}}                     

(b)  \frac{n}{{\sqrt{2}}}

(c)  2\sqrt{2}n                                         

(d)  \sqrt{2}n

Ans  (c)

6.

A small bar magnet A oscillates in a horizontal plane with a period T at a place where the angle of dip is 60^o. When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian, its period will be

(a)      \frac{T}{{\sqrt{2}}}                                

(b)     T

(c)      \sqrt{2}T

(d)     2T

Ans  (a)

7.

A tangent galvanometer has a coil with 50 turns and radius equal to 4 cm. A current of 0.1 A is passing through it. The plane of the coil is set parallel to the earth’s magnetic meridian. If the value of the earth’s horizontal component of the magnetic field is 7\times {{10}^{{-5}}}tesla and {{\mu }_{0}}=4\pi \times {{10}^{{-7}}}weber/amp\times m, then the deflection in the galvanometer needle will be

 (a) 45^o                                    

(b)  48.2^o

(c)  50.7^o                                

(d)  52.7^o

Ans (b)

8.

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

(a)      4/3

(b)     (\sqrt{3}+1)/1

(c)      (\sqrt{3}+1)/(\sqrt{3}-1)                    

(d)     \sqrt{3}/1

Ans (d)

9.

Using a bar magnet P, a vibration magnetometer has time  period 2seconds. When a bar Q (identical to P in mass and size) is placed on top of P, the time period is unchanged. Which of the following statements is true

(a)  Q is of non-magnetic material

(b)  Q is a bar magnet identical to P, and its north pole placed on top of P‘s north pole

(c)  Q is of unmagnetized ferromagnetic material

(d)  Nothing can be said about Q‘s properties

Ans (b)

10.

A certain amount of current when flowing in a properly set tangent galvanometer, produces a deflection of 45°. If the current be reduced by a factor of \sqrt{3}, the deflection would

(a)  Decrease by 30°          

(b)  Decrease by 15°

(c)  Increase by 15°            

(d)  Increase by 30°

Ans (b)

11.

The bob of a simple pendulum is replaced by a magnet. The oscillations are set along the length of the magnet. A copper coil is added so that one pole of the magnet passes in and out of the coil. The coil is short-circuited. Then which one of the following happens

(a)  Period decreases

(b)  Period does not change

(c)  Oscillations are damped

(d)  Amplitude increases

Ans (c)

12.

Two short magnets having magnetic moments in the ratio 27 : 8, when placed on opposite sides of a deflection magnetometer, produce no deflection. If the distance of the weaker magnet is 0.12 m from the centre of deflection magnetometer, the distance of the stronger magnet from the centre is 

(a)  0.06 m                             

(b)  0.08 m

(c)  0.12 m                             

(d)  0.18 m

Ans (d)

13.

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 freely in the same field. If its period of oscillation is T ¢, then ratio \frac{{{T}’}}{T}is

(a)      \frac{1}{4}    

(b)     \frac{1}{{2\sqrt{2}}}

(c)      \frac{1}{2}    

(d)     2

Ans (c)

14.

Two identical bar magnets are placed on above  the other such that they are mutually perpendicular and bisect each other. The time period of this combination in a horizontal magnetic Field is T. The time period of each magnet in the same field is

(a)       {{2}^{{\frac{1}{4}}}}T

(b)       {{2}^{{-\frac{1}{4}}}}T                                   

(c)       {{2}^{{-\frac{1}{2}}}}T

Ans (b)