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Engineering
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A current i ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

  • Option 1)

    infinite

  • Option 2)

    zero

  • Option 3)

    \frac{\mu _{0}}{4\pi }.\frac{2i}{r}\, tesla

  • Option 4)

    \frac{2i}{r}\, tesla

 
As we learnt in Magnetic field inside thin hollow cylinder - B=0 - wherein         Magnetic field will be zero inside the straight thin walled tube according to ampere's theorem. Option 1) infinite Incorrect option Option 2) zero Correct option Option 3) Incorrect option Option 4) Incorrect option
Engineering
236 Views   |  

A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B It is then bent into a circular loop of  n turns. The magnetic field at the centre of the coil will be

  • Option 1)

    nB

  • Option 2)

    n^{2}B

  • Option 3)

    2nB

  • Option 4)

    2n^{2}B

 
As we discussed in Magnetic Field due to Circular Current at the centre - If a coil of radius r is carrying current i then magnetic feild at a distnace X from its centre is: - wherein       Option 1) Incorrect option Option 2) Correct option Option 3) Incorrect option Option 4) Incorrect option
Engineering
121 Views   |  

The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54\mu T. What will be its value at the centre of the loop ?

  • Option 1)

    250\mu T

  • Option 2)

    150\mu T

  • Option 3)

    125\mu T

  • Option 4)

    75\mu T

 
As we discussed in Magnetic Field at the axis due to circular current carrying wire - - wherein N is numbers of turn in coil     Magnetic Field due to Circular Current at the centre - If a coil of radius r is carrying current i then magnetic feild at a distnace X from its centre is: - wherein           Option 1) Correct option Option 2) Incorrect option Option 3) Incorrect...
Engineering
96 Views   |  

Two long conductors, separated by a distance  d  carry current I_{1}\; and \; I_{2}   in the same direction .They exert a force  F on each other Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d . The new value of the force between them is

  • Option 1)

    -2F

  • Option 2)

    F/3

  • Option 3)

    -2F/3

  • Option 4)

    -F/3

 
As we discussed in Force between two parallel current carrying conductors - - wherein I1 and I2 current carrying two parallel wires  a-seperation between two wires        Option 1) Incorrect option Option 2) Incorrect option Option 3) Correct option Option 4) Incorrect option
Engineering
352 Views   |  

The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is 2 s. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

  • Option 1)

    2 s

  • Option 2)

    \frac{2}{3}\; s\;

  • Option 3)

    \; \; \; (2\sqrt{3})s\; \;

  • Option 4)

    \; \left ( \frac{2}{\sqrt{3}} \right )s

 
As we learnt in Time Period of Freely Suspended Magnet - - wherein I - Moment of Inertia     For a vibrating magnet,      where         (For three pieces together)        (For three pieces together) Option 1) 2 s Incorrect Option 2) Correct Option 3) Incorrect Option 4) Incorrect
Engineering
368 Views   |  

The materials suitable for making electromagnets should have

  • Option 1)

    high retentivity and high coercivity

  • Option 2)

    low retentivity and low coercivity

  • Option 3)

    high retentivity and low coercivity

  • Option 4)

    low retentivity and high coercivity.

 
As we learnt in Coercivity (H) - When H = Hc , B = 0 - wherein i.e  Magnetising fields (H) required to destroy the residual magnetism.     Retentivity - When H=0 (after having increases from 0 to Hs), B=Br Br - residual magnetism, retentivity -    Materials of low retentivity and low coercivity are suitable for making electromagnets. Option 1) high retentivity and high...
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