Two short magnets of equal dipole moments M are fastened perpendicularly at their centres (figure). The magnitude of the magnetic field at a distance d from the centre on the bisector of the right angle is :

1. μ04π Md3 

2. μ04π M2d3

3. μ04π 22Md3

4. μ04π 2Md3

 

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Two identical bar magnets with a length 10 cm and weight 50 gm-weight are arranged freely with their like poles facing in a inverted vertical glass tube. The upper magnet hangs in the air above the lower one so that the distance between the nearest pole of the magnet is 3mm. Pole strength of the poles of each magnet will be

(a) 6.64 amp×m

(b) 2 amp×m

(c) 10.25 amp×m

(d) None of these

Concept Questions :-

Analogy between electrostatics and magnetostatics
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If ϕ1 and ϕ2 be the angles of dip observed in two vertical planes at right angles to each other and ϕ be the true angle of dip, then

1. cos2ϕ=cos2ϕ1+cos2ϕ2

2. sec2ϕ=sec2ϕ1+sec2ϕ2

3. tan2ϕ=tan2ϕ1+tan2ϕ2

4. cot2ϕ=cot2ϕ1+cot2ϕ2

Concept Questions :-

Earth's magnetism
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Each atom of an iron bar (5 cm × 1 cm × 1 cm) has a magnetic moment 1.8×10-23 Am2 . Knowing that the density of iron is 7.78×103 kgm-3 atomic weight is 56 and Avogadro's  number is 6.02×1023 the magnetic moment of the bar in the state of magnetic saturation will be

1. 4.75 Am2                  2. 5.74 Am2

3. 7.54 Am2                  4. 75.4 Am2

Concept Questions :-

Analogy between electrostatics and magnetostatics
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A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds. The same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds. Then the angle of dip is

1. 0o                             2. 30o

3. 45o                           4. 90o

Concept Questions :-

Earth's magnetism
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A dip needle lies initially in the magnetic meridian when it shows an angle of dip θ at a place. The dip circle is rotated through an angle x in the horizontal plane and then it shows an angle of dip θ' . Then tan θ'tan θ is

1. 1/cos x

2. 1/sin x

3. 1/tan x

4. cos x

 

Concept Questions :-

Earth's magnetism
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A bar magnet has coercivity 4×103 Am-1. It is desired to demagnetize it by inserting it inside a solenoid 12 cm long and having 60 turns. The current that should be sent through the solenoid is

1. 2 A                            2. 4 A

3. 6 A                            4. 8 A

Concept Questions :-

Curie law and hyterisis
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For substances hysteresis (B - H) curves are given as shown in figure. For making temporary magnet which of the following is best.

(a) 

(b)

(c)

(d)

Concept Questions :-

Curie law and hyterisis
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The variation of magnetic susceptibility (χ) with temperature for a diamagnetic substance is best represented by

1. 

2. 

3. 

4. 

Concept Questions :-

Magnetic materials
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The variation of magnetic susceptibility (χ) with absolute temperature T for a ferromagnetic material is

Concept Questions :-

Curie law and hyterisis
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Difficulty Level: