Objective Questions on Magnetic Field

  1. A 2 m long conductor, carries a electric current of 50 A at a magnetic field of 100 × 10 − 3 T. The force on the conductor is

    The magnetic of the force on the conductor, F in the case of conductor of length l meter arranged at right angles to the magnetic field B tesla and carrying a electric current I, is given by F = BIP

  2. Materials which lack permanent magnetic dipoles are called

    Materials which lack permanent magnetic dipoles are called diamagnetic. Unlike a ferromagnet, a diamagnet is not a permanent magnet. Its magnetic permeability is less than μ0 (the permeability of free space).

  3. Which of the following is the ferroelectric material ?

    Ferroelectricity is a property of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. The term is used in analogy to ferromagnetism. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt. Potassium dihydrogen phosphate and Barium titanate are also examples of ferroelectric materials.

  4. Materials having a high dielectric constant, which is non-linear, are known as

    Because of its property of electric polarization.

  5. In ferromagnetic materials

    In ferromagnetic materials the atomic magnetic moments are parallel.

  6. When the atomic magnetic moments are randomly oriented in a solid its magnetic behavior is termed as

    When the atomic magnetic moments are randomly oriented in a solid its magnetic behavior is termed as paramagnetic.

  7. The intensity of magnetization, M, of a ferro magnetic solid

    The intensity of magnetization of a ferro magnetic solid is independent of temperature.

  8. When a ferromagnetic substance is magnetized small changes in dimensions occur. Such a phenomenon is known as

    Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization.

  9. Magnetic recording tape is most commonly made from

    Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic film. Magnetic recording tape is most commonly made from silicon - iron .

  10. The permeability of iron can be increased by

    The permeability of iron can be increased by alloying with cobalt.

  11. A material with unequal anti-parallel atomic magnetic moments is

    An anti-ferromagnet is a material with unequal anti-parallel atomic magnetic moments.

  12. The temperature beyond which substances lose their ferroelectric properties, is known as

    Materials are only ferromagnetic below their corresponding curie temperatures. Ferromagnetic materials are magnetic in the absence of an applied magnetic field. Curie temperature or curie point, is the temperature where a material's permanent magnetism changes to induced magnetism or vice versa.

  13. Positive magnetostriction exists when

    During magnetization process of magnet the dipoles are attract and repel each other. Positive magnetostriction exists when dipoles are repel each other.

  14. The energy stored in the magnetic field at a solenoid 10cm long and 4cm diameter wound with 2000 turns of wire carrying a electric current at 20 A, is

    L = ( N2μ0A ) / L = (( 2000 × 2000)(4π × 10 − 7)(π / 4)(16 × 10 − 4)) / 0.1 = 0.06 H
    Energy = ( 1 / 2 ) × (0.06) (400) = 12 joules.

  15. Two coils have inductances L1 = 1200 mH and L2 = 800 mH. They are connected in such a way that flux in the two coils aid each other and inductor is measured to be 2500 mH then Mutual inductor between the coils is ___________ mH.

    Flux in two coils aid each other inductor of the combination
    L = L1 + L2 + 2 × M
    2500 = 1200 + 800 + 2 × M
    2 × M = 500 or M = 250 mH.

  16. the coils having self inductor of 10 mH and 15 mH have an effective inductor of 40 mH , when connected in series aiding. What will be the equivalent inductor if we connect them in series opposing

    L = L1 + L2 + 2M, when ordinary
    40 = 10 + 15 + 2M
    2M = 15 mH
    L = L1 + L2 - 2M , when opposing
    L = 10 mH

  17. 1 Tesla =

    1 Tesla = 1 wb / m2

  18. Two parallel plates are separated by a distance of d meter and voltage pap plied across the is V volts. The field intensity is given by

    The field intensity can be defined as voltage per unit distance, hence = V ⁄ d

  19. In an AC circuit, containing pure inductance, the voltage applied is 120 V, 50 Hz while the electric current is 10 A. Find the value of inductance.

    XL ( inductive reactance ) = V ⁄ I = 120 ⁄ 10 = 12 Ω, XL = ΩL = 2πfL or, L = XL ⁄ (2π50) = 38 mH.

  20. A conductor of length l meters moves at right angles to a uniform magnetic field of flux density B = 1.5 T. if the velocity of revolution of the conductor is 50 ms-1 then induced e.m.f. in the conductor is

    e = Blvsinφ (φ = π/2)
    e = Blv = 1.5 × 1 × 50 = 75 V