Electromagnetic theory miscellaneous

Electromagnetic theory miscellaneous

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Electromagnetic Theory

Electromagnetic theory miscellaneous
  1. A point charge Q is located on the surface of a sphere of radius R as shown in the figure. The average electric field on the surface of the sphere will be—








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    The point charge Q elevates a total electric displacement flux of Q. If a plane is passed through the point of location of charge and tangential to the sphere, half the flux is on one side and half on the other. The first half of flux is passing through the spherical surface. Thus the average displacement density has a direction opposite to that of

    →
    n

    and the magnitude is
    Q/2
    4∏R2

    so, average electric field is
    Eav =
    Q
    		–→where,–→is the unit vector.
    8∏∈0R2(-n)n

    Correct Option: C

    The point charge Q elevates a total electric displacement flux of Q. If a plane is passed through the point of location of charge and tangential to the sphere, half the flux is on one side and half on the other. The first half of flux is passing through the spherical surface. Thus the average displacement density has a direction opposite to that of

    →
    n

    and the magnitude is
    Q/2
    4∏R2

    so, average electric field is
    Eav =
    Q
    		–→where,–→is the unit vector.
    8∏∈0R2(-n)n

  1. Two point charges Q and – Q are located on two opposite corners of a square as shown in figure. If the potential at the corner A is taken as 1 V, then the potential at B, the centre of the square will be—








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    The plane midway between a and – a, i.e., the one passing through ABC and perpendicular to the plane of the paper is an equipotential plane.
    Hence the potential at B is the same as that of A or C, i.e., 1 V.

    Correct Option: C

    The plane midway between a and – a, i.e., the one passing through ABC and perpendicular to the plane of the paper is an equipotential plane.
    Hence the potential at B is the same as that of A or C, i.e., 1 V.

  1. Transmission of power to a load over a transmission line achieves optimum value when standing-wave ratio (SWR) becomes—








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    Transmission of power to a load over a transmission line achieves optimum value when SWR becomes 1.

    Correct Option: C

    Transmission of power to a load over a transmission line achieves optimum value when SWR becomes 1.

  1. When electromagnetic waves are reflected at an angle from a wall, their wavelength along the wall is—








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    The wavelength along the wall is greater than in the actual direction of propagation.

    Correct Option: D

    The wavelength along the wall is greater than in the actual direction of propagation.

  1. Frequencies in UHF range propagate by means of—








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    Frequencies in UHF range propagate by means of space waves.

    Correct Option: C

    Frequencies in UHF range propagate by means of space waves.