Objective Questions on Electric Field

  1. According to Coulomb’s law, the force of attraction or repulsion, between to electrical charges is

    Coulomb’s law states that the force of attraction or repulsion, F between two charges q1 and q2 coulombs, connected at two different points in a medium, is directly proportional to the product of their magnitude and inversely proportional to the square of distance r between them.

  2. Permittivity of free space is equal to

    Permitivity of free space is equal to 8.84 × 10 - 12 F / m.

  3. Absolute permittivity of a dielectric medium is represented by

    The absolute permittivity of a dielectric medium is expressed as ε = εoεr
    Where, εo is the permittivity of free space and εr is the relative permittivity of the medium.

  4. Ohm’s law in point from field theory can be expressed as

    In linear medium, the conduction electric current density is proportional to the applied electric field:
    J = σE = E / ρ [ A / m2]
    where, σρ = 1 / r [ S / m ( Siemens / meter ) ] is the conductivity and ρr [ Ohm - meters] is the resistivity of the material. This equation is clearly related to the Ohm’s law of circuit theory; in field theory, it is called the point form of Ohm’s law .

  5. The dielectric strength of ferroelectric materials depends to a large extent on

    The dielectric strength of ferroelectric materials depends to a large extent on intensity of electric field.

  6. Ampere second is the unit of

    Current is transfer electrical charge per second. Therefore Ampere = coulomb / second hence coulomb = ampere × second or ampere second.

  7. A metal surface with 1 meter radius and surface charge density of 20 coulombs / m2 is enclosed in a 10 m side. The total outward electric displacement normal to the surface, the cube is

    D = q × 4πr2 = 20 × 4π12 = 80π coulombs.

  8. Inside a hollow conducting sphere

    For any concentric sphere inside conducting sphere, charge enclosed is zero hence electric field is zero is zero.

  9. A long wire composed of a smooth round conductor runs above and parallel to the ground (assumed to be a large conducting plane). A high voltage exists between the conductor and the ground. The maximum electric stress occurs at

    Electric stress is more at between the conductor and ground (because of capacitance effect). The maximum electric stress occurs at lower surface of the conductor because of maximum field intensity.

  10. The energy stored in the magnetic field at a solenoid 30 cm long & 3 cm diameter wound with 100 turns of wire carrying a electric current at 10 amp, is

    Under construction

  11. The voltage across R and L in a series RL circuit are found to be 200 V and 150 V respectively the rms value of the voltage across the series combination is ______ V.

    Voltage across series combination V = √(V2R × V2L) = √(2002 + 150 2) = 250 V.

  12. Three identical resistor are connected in star across a 3 phase 550 V supply dissipating a total power of 300 W the line electric current is ____________ A.

    Power consumed = 300 = √3VL × ILcosφ
    Since cosφ = 1; i.e resistive load, IL = 300 / 550 × √3 = 3.149 A.

  13. A motor having a power factor of 0.8 absorbs in active power of 1200 W the reactive power drawn from the supply is _________ VA.

    VI sinφ = reactive power , Active power = 1200 W , cosφ = 0.8
    VI = 1200 / 0.8, reactive power = 1200 / 0.8 × 0.6 = 900 VA.

  14. A coil of negligible resistance has an induction of 100 mH. The electric current passing through the coil changes from 2 A to 4 A at a uniform rate in 0.1 sec the voltage across the coil during this time would be __________ V.

    V = L × di / dt = 100 × 10-3 × 2 / 0.1 = 2 Volts.

  15. The instantaneous values of line electric current into a delta connected load in any two lines are + 2.5 amps and - 1.25 amps the electric current in the third line at the instant is ___________ A.

    Since at any instant the vector sum of electric current must be zero.

  16. A electric current of 4 A flows in an ac circuit when 100 V dc is applied to it whereas it takes 250 v ac to produce the same electric current the power factor of the circuit is

    With dc R = V / I = 100 / 4 = 25 ohms
    With ac Z = V / I = 250 / 4 = 62.5 ohms
    cosφ = R / Z = 25 / 62.5 = 0.4.

  17. The strength of electric current in 1 H inductor changes at rate of 1 A / sec. Find the voltage across it?

    L = 1 H.
    di / dt = 1 A / sec.
    V = L × di / dt = 1 × 1 = 1 V.

  18. Constant K type HPF (high pass filter) having cut off frequency 12 KHz and nominal impedance Ro = 500 Ω Find shunt arm inductor L and series arm capacitance C for T and π section of HPF ?

    L = Ro / 4πfc = 500 / 4 × 3.14 × 12 × 1000 = 3.316 mH ;
    C = 1 / 4πRcfc = 1 / 4 × 3.14 × 500 × 12 × 1000 = 0.0132 μF.

  19. In foster 1 form 1st element is

    In foster 1 form 1st element Co (pole at Ω = 0) and last element is L (pole at Ω = ∞)
    In foster 2 reverse thing is present .

  20. In 2 port network Z12 = Z21 indicates which property

    In 2 port network Z12 = Z21 indicates bilateral property .