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

added to produce about 12 grades.

⦁ 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

⦁

**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

⦁ Faraday’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

⦁

**about 1837 times**
⦁ 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

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