Q.1
Relative permeability of vacuum is
Q.2
In a magnetic material hysteresis loss takes place primarily due to
Q.3
Permeability in a magnetic circuit corresponds to_________ in an electric circuit.
Q.4
The unit for reluctance is
  • tesla
  • At/Wb
  • At/m
  • Wb
Q.5
Those materials are well suited for making permanent magnets whichhave______retentivity and _______coercivity.
  • low, high
  • high, high
  • high, low
  • low, low
Q.6
Point out the wrong statement.Magnetic leakage is undesirable in electric machines because it
  • lowers their power efficiency
  • increases their cost of manufacture
  • leads to their increased weight
  • produces fringing
Q.7
Permeability in a magnetic circuit corresponds to______ in an electric circuit.
  • resistance
  • resistivity
  • conductivity
  • conductance
Q.8
If a loop in a basic dc generator suddenly begins rotating at a faster speed, the induced voltage
  • remains unchanged
  • reverses polarity
  • increases
  • decreases
Q.9
What is the magnetomotive force (mmf) of a wire with 8 turns carrying three amperes of current?
  • 2,400 At
  • 240 At
  • 24 At
  • 2.4 At
Q.10
When a solenoid is activated, the force that moves the plunger is
  • an electromagnetic field
  • a permanent magnetic field
  • varying voltage
  • a steady current
Q.11
An electromagnetic field exists only when there is
  • an increasing current
  • decreasing current
  • voltage
  • current
Q.12
The direction of a magnetic field within a magnet is
  • from south to north
  • from north to south
  • back to front
  • front to back
Q.13
When the north poles of two bar magnets are brought close together, there will be
  • no force
  • a downward force
  • a force of attraction
  • a force of repulsion
Q.14
The ability of a material to remain magnetized after removal of the magnetizing force is known as
  • permeability
  • reluctance
  • hysteresis
  • retentivity
Q.15
The induced voltage across a stationary conductor in a stationary magnetic field is
  • zero
  • reversed in polarity
  • increased
  • decreased
Q.16
What is the magnetomotive force in a 75-turn coil of wire when there are 4 A of current through it?
  • 18.75 At
  • 30 At
  • 300 At
  • 187 At
Q.17
The unit for permeability is
  • Wb/At × m
  • At/m
  • At/Wb
  • Wb
Q.18
A basic one-loop dc generator is rotated atrev/s. How many times each second does the dc output voltage peak (reach maximum)?
  • 90
  • 180
  • 270
  • 360
Q.19
When the current through the coil of an electromagnet reverses, the
  • direction of the magnetic field reverses
  • direction of the magnetic field remains unchanged
  • magnetic field expands
  • magnetic field collapses
Q.20
If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density
  • increases
  • decreases
  • remains the same
  • doubles
0 h : 0 m : 1 s