ELECTRICITY AND MAGNETISM FUNDAMENTALS Multiple Choice Questions Part 1

1 Temporary magnets are commonly employed in
electric instruments
motors
moving coils loudspeakers
magnetos

2 If the distance between two magnetic poles decreases by 2 times, the force between them
decreases two times
increases four times
increases two times
decreases four times

3 The force between two magnetic poles is  the relative permeability of the medium.
directly proportional to
independent of
inversely proportional to
equal to

4 The unit of flux density is
Wb/m
Tesla
At/m
N/Wb

5 Magnetic field intensity is a  quantity.
scalar
phasor
vector
variable

6 The relative permeability of a magnetic material is 10^5. What is its permeability?
⦁      4n × 10^5 H/m
⦁      4n × 10^-12 H/m
⦁      4v × 10^-2 H/m
⦁      4n × 10^-7 H/m

7 Which of the following has the highest permeability?
Soft iron
Steel
Air
Permalloy

8 As the magnetic intensity decreases, the relative permeability of a magnetic material
decreases
remains the same
increases
becomes zero

9 When the  relative  permeability of a  material  is  slightly less than 1,  it  is called
material.
diamagnetic
ferromagnetic
paramagnetic
non-magnetic

10 When the relative permeability of a material is slightly more than 1, it is called
material.
diamagnetic
ferromagnetic
paramagnetic
non-magnetic

11 Which of the following is a diamagnetic material?
Aluminum
Silver
Air
Cobalt

12 The greater percentage of materials is  .
diamagnetic
paramagnetic
ferromagnetic
non-magnetic

13 When the relative permeability of a material is much greater than 1, it  is called
material.
diamagnetic
ferromagnetic
paramagnetic
non-magnetic

14 At/m is a unit of
mmf
magnetic force
reluctance
magnetic flux density

15 The direction of force o a current carrying conductor placed in a magnetic field can be found by
Cork screw rule
Fleming’s left hand rule
Fleming’s right hand rule
using a compass

16 A commercial alloy of aluminum nickel, and iron with cobalt, copper and titanium
Brass
Alnico
Aluminum
Constantan

17 The physical motion resulting from the forces of magnetic fields is called.
Rotation
Motor action
Repulsion
Torque action

18 The flux density in an air-cored coil is 10^-3 Wb/m^2. With a cast iron core of relative
permeability 100 inserted, the flux density will become
⦁ 10^-3 Wb/m^2
⦁ 10^-2 Wb/m^2
⦁ 10^3 Wb/m^2
⦁  0.1 Wb/m^2

19 The permeability of a material having a flux density of 5 Wb/m^2 is 10^-5 H/m. What is the value of magnetizing force?
⦁  5 × 10^-5 N/Wb
⦁  500 × 10^3 N/Wb
⦁  4n × 10^-7 N/Wb
⦁  4n × 10^7 N/Wb

20 A magnetic pole produces 5000 field lines. How much is the flux in webers?
⦁  50 × 10^-6
⦁  5 × 10^-6
⦁  500 × 10^-6
⦁  500 × 10^-5

21 The force acting on a pole of 5 Wb is 25 N. What is the intensity of the magnetic field?
⦁  5 N/Wb
25 N/Wb
125 N/Wb
0.2 N/Wb

22 A magnetic circuit carries a flux 6i in the iron part and a flux 6g in the air gap. What is the leakage coefficient?
'i/ 'g
6i × 6g
6g /6i
6i + 6g

23 The reluctance of the magnetic circuit is  _ relative permeability of the material comprising the circuit.
directly proportional to
inversely proportional to
independent of
dependent of

24 A law relating between the magnetic and electric susceptibilities and the absolute temperatures which is followed b ferromagnets, antiferromagnets, non-polar ferroelectrics, antiferroelectrics and some paramagnets.
Curie’s Law
Child’s Law
CR Law
Curie-Weiss Law

25 Theory of ferromagnetic phenomena which assumes each atom is a permanent magnet which can turn freely about its center under the influence of applied field and other magnets.
Ewing’s theory of ferromagnetism
Oersted’s ferromagnetism theory
Maxwell’s magnetic theory
Ampere’s circuital law

26 The reluctance of a magnetic circuit varies with
length × area
area ÷ length
length ÷ area
length + area

27 A theorem which states that an electric current flowing in a circuit produces a magnetic field at external points equivalent to that due to a magnetic shell whose bounding edge is the conductor and whose strength of the current.
Joule’s law
Volta’s theorem
Ampere’s theorem

28 What is the usual value of leakage coefficient for electrical machines?
0.5 to 1
1 to 5
5 to 10
⦁.     1.15 to 1.25

29 The reluctance of a magnetic circuit is not dependent on which of the following?
Number of turns of coil
Magnetomotive force
Flux density in the circuit
Current in the coil

30 Another term for corona discharge.
Lightning
Sparking
Aurora
Corona Effect

31 The B-H curve for  is a straight line passing through the origin.
cobalt
air
hardened steel
soft iron

32 The phenomenon that when an electric current passes through an anisotropic crystal, there is an absorption or liberation of heat due to the non-uniformity in current distribution.
Bridgman effect
Corona effect
Dember effect
Destriau effect

33 If a magnetic flux cuts across 200 turns at a rate of 2Wb/s, the induced voltage  according to Faraday’s law is about
400 V
100 V
200 V
600 V

34 Hysteresis loss can be reduced by one of the following.
Increasing mmf of the circuit
Using material narrow hysteresis loop
Using ferromagnetic core
Laminating the magnetic circuit

35 Which of the following materials has the least hysteresis loop area?
soft iron
silicon steel
hard steel
wrought iron

36 Core materials of a good relay have  hysteresis loop.
large
narrow
very large
very narrow

37 The magnetic materials should have a large hysteresis loss for one of the following applications.
Transformers
AC motors
Permanent Magnets
DC generators

38 What is the measure of the density and sign of the electric charge at a point relative to that at some time?
Electric potential
Electric charge
Electric current
Electric intensity

39 The mass of proton is  the mass of an electron.
equal to
less than
200 times

40 If the number of valence electrons of an atom is less than 4, then the substance is probably
a metal
an insulator
a non-metal
a semiconductor

41 The resistance of a material is  its area of cross-section.
directly proportional
independent of
inversely proportional to
equal to

42 If the length and area of cross-section of a wire are doubled, then its resistance
becomes four times
becomes sixteen times
remains the same
becomes two times

43 A length of wire has a resistance of 10 ohms. What is the resistance of a wire of the same material three times as long and twice the cross-sectional area?
30 ohms
20 ohms
15 ohms
7 ohms

44 What is the SI unit of specific resistance or resistivity?
Ohm-circular mil per inch
Ohm-circular mil per foot
Ohm-m
Ohm-cm

45 The temperature coefficient of resistance of semiconductors is
positive
zero
negative
infinite

46 What determines the value of the temperature coefficient of resistance of a material?
length
cross-sectional area
volume
nature and temperature

47 The  temperature  coefficient  of resistance  of a conductor  with an increase in temperature.
increases
decreases
remains the same
becomes negative

48 The temperature coefficient of resistance of insulators is
zero
negative
positive
infinite

49 The temperature coefficient of resistance of eureka is
positive
negative
almost zero
infinite

50 If the number of valence electrons of an atom is more than 4, the substance is called
a semiconductor
a conductor
an insulator
a semi-insulator