Electromagnetic Theory and Transmission Lines Mid - I, February - 2012

1.The field intensity due to a point charge Q at a distance, R, is E1. If charge is increased to ‘4Q’ and distance is increased to ‘2R’, the field intensity E2 becomes
  • E2 = E1
  • E2 = 4E1
  • E2 = 2E1
  • E2 = E1/2
Answer: A
2.A wire of 1mm diameter with conductivity of 5�10^7 mho/m has 10^ 20 electrons per unit volume. The conduction current density for an applied field of 10 mV/m is
  • 5×10^ 7 A / m^ 2
  • 5×10^ -9 A/m^2
  • 5×10^- 3 A/m^2
  • 500 kA/m^2
Answer: B
3.Identify the Maxwell’s equation which is not in phasor form
  • ▼xE =-jwB
  • ▼xE=-ÝBÝt
  • ▼× H=jwD+J
  • ▼×D=ρ v
Answer: B
4.Identify Maxwell’s equation which is not applicable for static fields
  • ▼ × E = 0
  • ▼ × H = J + ∂ D ∂ t
  • ▼ × H = ∂ D ∂ t
  • ▼ × E = - ∂ B ∂ t
Answer: A
5.Normal component of B is continuous at
  • Any discontinuity
  • Dielectric - Dielectric interface only
  • Conductor - conductor interface only
  • Dielectric- Conductor interface only.
Answer: A
6.Units of magnetic field intensity are
  • Amperes/meter
  • Webers/ meter
  • Amperes
  • Webers
Answer: A
7.Electrostatic field being conservative doe s not mean
  • Its circulation is identically zero
  • the work done in side a closed path inside the field is zero
  • The potential difference between any two point s is zero
  • it is the gradient of a scalar potential
Answer: C
8.For a dielectric - dielectric interface at the boundary,
  • Tangential component of H is non - continuous by the amount of current density on the interface
  • Tangential component of H is continuous
  • Tangential component of E is not continuous
  • Tangential component of H is not continuous
Answer: B
9.At a conductor interface with surface charge density
  • Tangential component of E is not continuous
  • Normal component of B is not continuous
  • Tangential component of H is continuous
  • Normal component of D is not continuous
Answer: D
10.A charge Q is uniformly distributed in a sphere of radius a1 the charge density, if the same charge Q is made to occupy a sphere of radius a2=a1/4 is
  • 16 times more
  • 4 times more
  • 64 times more
  • 2 times more
Answer: C
11.Exponential decay of charge density with time is based on the time constant T, referred to as _____.
Answer: Relaxation time.
12.Units of permeability are ___________.
Answer: Henrys /meter.
13.Force on a moving charge due to electric and magnetic fields is given by __________.
Answer: F=e (E+v×B)
14.The magnetic field at a point ρ distance away in the normal direction t o an infinite current element is given by _________.
Answer: H=I2ðñaö
15.At a conductor interface with surface charge density Normal component of D is __________.
Answer: Not continuous
16.If the electric flux density, D and electric field intensity, E are not in the same direction, the material is called as ____________
Answer: Anisotropic medium.
17.The unit of magnetic susceptibility __________.
Answer: No units
18.Value of permeability of free space is ___________.
Answer: 4π x 10^-7 H/ m.
19.According to _________,electrical flux due to any closed surface is equal to the charge enclosed by the surface.
Answer: Gauss’s law
20.Point charges 30 nC , - 20nC and 10 nC are located at (-1,0, 2) , (0,0, 0) and (1,5,-1) respectively. The total flux leaving a cube of side 6m centered at the origin is ________.
Answer: 10NC