Electromagnetics Set 15

Electrical Engineering

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This set of Electromagnetics Multiple Choice Questions & Answers (MCQs) focuses on Electromagnetics Set 15

Q1 | The electromagnet has 50 turns and a current of 1A flows through the coil. If the lengthof the magnet circuit is 200 mm, what is the magnetic field strength ?
  • 2500 at/m
  • 250 at/m
  • 25 at/m
  • 2.5 at/m
Answer: 250 at/m
Q2 | A square cross-sectional magnet has a pole strength of 1 x 10 Wb and cross sectionalarea of 20 mm x 20 mm. What is the strength at a distance of 100 mm from the unit pole in air ?
  • 63.38 n/wb
  • 633.8 n/wb
  • 6338 n/wb
  • 63380 n/wb
Answer: 6338 n/wb
Q3 | The unit of flux is the same as that of
  • reluctance
  • resistance
  • permeance
  • pole strength
Answer: pole strength
Q4 | Unit for quantity of electricity is
  • ampere-hour
  • watt
  • joule
  • coulomb
Answer: coulomb
Q5 | The Biot-savart's law is a general modification of
  • kirchhoffs law
  • lenz\s law
  • ampere\s law
  • faraday\s laws
Answer: ampere\s law
Q6 | The most effective and quickest may of making a magnet from soft iron is by
  • placing it inside a coil carrying current
  • induction
  • the use of permanent magnet
  • rubbing with another magnet
Answer: placing it inside a coil carrying current
Q7 | The commonly used material for shielding or screening magnetism is
  • copper
  • aluminium
  • soft iron
  • brass
Answer: soft iron
Q8 | If a copper disc is rotated rapidly below a freely suspended magnetic needle, themagnetic needle shall start rotating with a velocity
  • less than that of disc but in opposite direction
  • equal to that of disc and in the same direction
  • equal to that of disc and in the opposite direction
  • less than that of disc and in the same direction
Answer: less than that of disc and in the same direction
Q9 | A permanent magnet
  • attracts some substances and repels others
  • attracts all paramagnetic substan¬ces and repels others
  • attracts only ferromagnetic sub¬stances
  • attracts ferromagnetic substances and repels all others
Answer: attracts some substances and repels others
Q10 | The retentivity (a property) of material is useful for the construction of
  • permanent magnets
  • transformers
  • non-magnetic substances
  • electromagnets
Answer: permanent magnets
Q11 | The relative permeability of materials is not constant.
  • diamagnetic
  • paramagnetic
  • ferromagnetic
  • insulating
Answer: ferromagnetic
Q12 | The materials are a bit inferior conductors of magnetic flux than air.
  • ferromagnetic
  • paramagnetic
  • diamagnetic
  • dielectric
Answer: diamagnetic
Q13 | Hysteresis loop in case of magnetically hard materials is more in shape as compared tomagnetically soft materials.
  • circular
  • triangular
  • rectangular
  • none of the above
Answer: rectangular
Q14 | A keeper is used to
  • change the direction of magnetic lines
  • amplify flux
  • restore lost flux
  • provide a closed path for flux
Answer: provide a closed path for flux
Q15 | The change of cross-sectional area of conductor in magnetic field will affect
  • reluctance of conductor
  • resistance of conductor
  • (a) and (b) b >th in the same way
  • none of the above
Answer: (a) and (b) b >th in the same way
Q16 | The uniform magnetic field is
  • the field of a set of parallel conductors
  • the field of a single conductor
  • the field in which all lines of mag¬netic flux are parallel and equidis¬tant
  • none of the above
Answer: the field in which all lines of mag¬netic flux are parallel and equidis¬tant
Q17 | The magneto-motive force is
  • the voltage across the two ends of exciting coil
  • the flow of an electric current
  • the sum of all currents embraced by one line of magnetic field
  • the passage of magnetic field through an exciting coil
Answer: the sum of all currents embraced by one line of magnetic field
Q18 | What will be the current passing through the ring shaped air cored coil when number ofturns is 800 and ampere turns are 3200 ?
  • 2
  • 4
  • 6
  • 8
Answer: 4
Q19 | What will be the magnetic potential difference across the air gap of 2 cm length inmagnetic field of 200 AT/m ?
  • 2 at
  • 4 at
  • 6 at
  • 10 at
Answer: 4 at
Q20 | The initial permeability of an iron rod is
  • the highest permeability of the iron rod
  • the lowest permeability of the iron rod
  • the permeability at the end of the iron rod
  • the permeability almost in non-magnetised state
Answer: the permeability almost in non-magnetised state
Q21 | How does the magnetic compass needle behave in a magnetic field ?
  • it assures a position right angle to magnetic field
  • it starts rotating
  • it assures a position which follows a line of magnetic flux
  • none of the above
Answer: it assures a position which follows a line of magnetic flux
Q22 | The stray line of magnetic flux is defined as
  • a line vertical to the flux lines
  • the mean length of a ring shaped coil
  • a line of magnetic flux in a non-uniform field
  • a line of magnetic flux which does not follow the designed path
Answer: a line of magnetic flux which does not follow the designed path
Q23 | The bar magnet has
  • the dipole moment
  • monopole moment
  • (a) and (b) both
  • none of the above
Answer: the dipole moment
Q24 | Which of the following materials are dia-magnetic ?
  • silver
  • copper
  • silver and copper
  • iron
Answer: silver and copper
Q25 | Which of the following type of materials are not very important for engineeringapplications ?
  • ferromagnetic
  • paramagnetic
  • diamagnetic
  • none of the above
Answer: diamagnetic
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