MCQOPTIONS
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MCQOPTIONS
This section includes 45 Mcqs, each offering curated multiple-choice questions to sharpen your Electromagnetic Theory knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Absolute permeability of a free space is: |
| A. | μ0 = 4π × 10-7 H/m |
| B. | μ0 = 4π × 10-6 H/m |
| C. | μ0 = 4π × 10-7 H/sq-m |
| D. | μ0 = 4π × 10-6 H/sq-m |
| Answer» B. μ0 = 4π × 10-6 H/m | |
| 2. |
In an electric magnetic circuit, for establishing a magnetic field: |
| A. | The movement of coil is required. |
| B. | Energy need not be spent, though energy is required to maintain it. |
| C. | Energy must be spent, though no energy is required to maintain it. |
| D. | Energy is not at all required. |
| Answer» D. Energy is not at all required. | |
| 3. |
Calculate the value of current flowing through a conductor (at rest) when a straight wire 3 m long (denoted as AB in the given figure) of resistance 3 ohm is placed in the magnetic field with the magnetic induction of 0.3 T.The conductor is connected to a voltage source of 3 V. |
| A. | I = 9 A |
| B. | I = 1 mA |
| C. | I = 1 A |
| D. | I = 3.3 A |
| Answer» D. I = 3.3 A | |
| 4. |
A rectangular iron core has three coils as shown in the given figure. The number of turns of the coils are Na = 300, Nb = 600 and Nc = 600, and the respective currents are 1.5 A, 4 A and 3 A. Find the total magnetomotive force. |
| A. | 1050 AT |
| B. | 3750 AT |
| C. | 4650 AT |
| D. | 1136 AT |
| Answer» B. 3750 AT | |
| 5. |
In parallel magnetic circuit, the total ampere turn is equal to the: |
| A. | ampere turn of only one smallest part |
| B. | ampere turn of only one longest part |
| C. | difference of ampere – turn of each path |
| D. | sum of amper – turn of each path |
| Answer» E. | |
| 6. |
In the magnetic circuit shown, below what is the flux density produced if the relative permeability of the core material under the given condition is 1000? |
| A. | 1 T |
| B. | 3 T |
| C. | 2 T |
| D. | 4 T |
| Answer» D. 4 T | |
| 7. |
A solid non-magnetic conductor of circular cross section has its axis on z-axis and carries a uniformly distributed total current of 60 A in the az direction. If the radius of the conductor is 4 mm, find the magnetic flux density at ρ = 5 mm |
| A. | 3.1 mT |
| B. | 2.1 mT |
| C. | 2.4 mT |
| D. | 4.0 mT |
| Answer» D. 4.0 mT | |
| 8. |
A conductor of axial length 30 cm carries a current of 100 A and lies at right angle to a magnetic field of strength 0.4 tesla. What is the force exerted on it? |
| A. | 10 N |
| B. | 12 N |
| C. | 1.2 N |
| D. | 0 |
| Answer» C. 1.2 N | |
| 9. |
If the current element represented by 4 × 10-4 ây Amp-m is placed in a magnetic field of \(\bar H = \frac{{5{{\hat a}_x}}}{\mu }A/m\), the force on the current element is |
| A. | -2.0 âz mN |
| B. | 2.0 âz mN |
| C. | -2.0 âz N |
| D. | 2.0 âz N |
| Answer» B. 2.0 âz mN | |
| 10. |
Consider a scenario in a DC motor. When a conductor of Length "L" is placed inside a magnetic field of strength "H", flux density "B" and current "I" is flowing through the conductor, then what will be the magnitude of force F acting on it? |
| A. | F=(B/iL) cos\(\theta\) newtons |
| B. | F=BiL sin\(\theta\) newtons |
| C. | F=B (-i) L sin\(\theta\) newtons |
| D. | F=BiL cos\(\theta\) newtons |
| Answer» C. F=B (-i) L sin\(\theta\) newtons | |
| 11. |
Ferromagnetic property may be explained on the basis of |
| A. | Faraday’s theory |
| B. | Curie-Weiss theory |
| C. | domain theory |
| D. | Einstein’s theory |
| Answer» D. Einstein’s theory | |
| 12. |
"M.M.F around any closed path equals the current enclosed by the path". This is known as _______. |
| A. | Coulomb's law |
| B. | Gauss' law |
| C. | Ampere's law |
| D. | Biot-Savart law |
| Answer» D. Biot-Savart law | |
| 13. |
For the circuit of the figure the inductor current iL just before t = 0 is |
| A. | 10 A |
| B. | 6 A |
| C. | 4 A |
| D. | 2 A |
| Answer» E. | |
| 14. |
A long straight circular conductor placed in air is carrying a current of 250 A. Find the magnetising force at a distance of 5 cm from the conductor. |
| A. | \(\frac{{5000}}{\pi }AT/m\) |
| B. | \(\frac{{500}}{\pi }AT/m\) |
| C. | 2500 AT / m |
| D. | \(\frac{{2500}}{\pi }AT/m\) |
| Answer» E. | |
| 15. |
A magnetising force of 800 AT/m will produce a flux density of ______ in air. |
| A. | 1 Wb/m2 |
| B. | 1 mWb/m2 |
| C. | 10 mWb/m2 |
| D. | 0.5 Wb/m2 |
| Answer» C. 10 mWb/m2 | |
| 16. |
In a pair of straight parallel bus bars of circular cross-section spaced 23 cm between centres, each carry a current of 70,000 A. The force required to withstand will be nearly |
| A. | 4,800 N/m |
| B. | 4,620 N/m |
| C. | 4,400 N/m |
| D. | 4,260 N/m |
| Answer» E. | |
| 17. |
A moving charge produces: |
| A. | an electric field only |
| B. | a magnetic field only |
| C. | Both an electric field & a magnetic field |
| D. | None of these |
| Answer» D. None of these | |
| 18. |
A slid cylindrical conductor of radius R has a uniform current density I. The magnetic filed H inside the conductor at distance r from the axis of the conductor is |
| A. | \(\frac{I}{2πr}\) |
| B. | \(\frac{I}{4πr}\) |
| C. | \(\frac{I~r}{2πR^2}\) |
| D. | \(\frac{I~r}{4πR^2}\) |
| Answer» D. \(\frac{I~r}{4πR^2}\) | |
| 19. |
lf a saw cut of 1 mm wide is made in the ring, calculate the current which will give same flux as in the previous question. Neglect leakage and fringing. |
| A. | 1.6 A |
| B. | 2.8 A |
| C. | 7 A |
| D. | 9.2 A |
| Answer» B. 2.8 A | |
| 20. |
For a given voltage, four heating coils will produce minimum heat when connected |
| A. | all in parallel |
| B. | all in series |
| C. | with two parallel pairs in series |
| D. | one pair in parallel with the other two in series |
| Answer» C. with two parallel pairs in series | |
| 21. |
Direction: Question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. Examine these two statements carefully and select the answer to this question using the codes given below:Assertion (A): Magnetic susceptibility value of an antiferromagnetic substance at 0° K is zero.Reason (R): At 0° K, atomic magnetic moments are frozen with magnetic dipoles pointing in random directions. |
| A. | Both A and R are individually true and R is the correct explanation of A |
| B. | Both A and R are individually true but R is not the correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» D. A is false but R is true | |
| 22. |
A bar magnet made of steel has a magnetic moment of 2.5 A-m2 and a mass of 6.6 × 103 kg. If the density of steel is 7.9 × 103 kg/m3 the intensity of magnetization is |
| A. | 8.3 × 10-7 A/m |
| B. | 3 A/m |
| C. | 6.3 × 10-7 A/m |
| D. | 8.2 × 106 A/m |
| Answer» C. 6.3 × 10-7 A/m | |
| 23. |
Determine the energy density in free space created by a magnetic field with intensity H = 103 A/m |
| A. | 314 mJ/m3 |
| B. | 314 μJ/m3 |
| C. | 628 mJ/m3 |
| D. | 628 μJ/m3 |
| Answer» D. 628 μJ/m3 | |
| 24. |
A plane wave travelling in a medium of εr = 1, μr = 1 (free space) has an electric field intensity of 100 √ π V/m. Determine the total energy density of this magnetic field. |
| A. | 13.9 nJ/m3 |
| B. | 27.8 nJ/m3 |
| C. | 139 nJ/m3 |
| D. | 278 nJ/m3 |
| Answer» D. 278 nJ/m3 | |
| 25. |
A transformer with toroidal core of permeability μ is shown in the figure. Assuming uniform flux density across the circular core cross-section of radius r R, and neglecting any leakage flux, the best estimate for the mean radius R is |
| A. | \(\frac{{\mu V{r^2}N_P^2\omega }}{I}\) |
| B. | \(\frac{{\mu I{r^2}{N_P}{N_S}\omega }}{V}\) |
| C. | \(\frac{{\mu V{r^2}N_P^2\omega }}{{2I}}\) |
| D. | \(\frac{{\mu I{r^2}N_P^2\omega }}{{2V}}\) |
| Answer» E. | |
| 26. |
A long wire carrying a certain current produces a magnetic field of 0.8 Tesla at a distance 0.5 cm. Then magnetic field at a distance of 1 cm is: |
| A. | 0.16 Tesla |
| B. | 0.2 Tesla |
| C. | 0.8 Tesla |
| D. | 0.4 Tesla |
| Answer» E. | |
| 27. |
One of the following is not a valid statement: |
| A. | Fleming’s right hand rule is used to find out the direction of current in the conductor of a generator |
| B. | Fleming’s left hand rule is used to find out the direction of rotation of the armature of DC motor |
| C. | Ampere’s rule is used to find out the direction of lines of force around the wire carrying current |
| D. | Right hand thumb rule is used to find out the direction of counter current produced in the armature magnetic field |
| Answer» E. | |
| 28. |
1 Tesla = _______ Weber/m2 |
| A. | 1 |
| B. | 10 |
| C. | 0.1 |
| D. | 100 |
| Answer» B. 10 | |
| 29. |
Calculate the current required to produce a flux of 1.75 mwb in the ring, if the relative permeability of the iron is 900. No.of turns N = 600, and radius of the cross-section r = 3.5 cm. |
| A. | 0.15A |
| B. | 0.35 A |
| C. | 0.5 A |
| D. | 0.10 A |
| Answer» B. 0.35 A | |
| 30. |
A uniform and constant magnetic field B ẑ. B̅ exists in the \({\rm{̂ z}}\) direction in vacuum. A particle of mass m with a small charge q is introduced into this region with an initial velocity v = x̂vx + ẑvz. Given that B, m, q, vx, and vz are all non-zero, which one of the following describes the eventual trajectory of the particle? |
| A. | Helical motion in the ẑ direction. |
| B. | Circular motion in the xy-plane. |
| C. | Linear motion in the ẑ direction. |
| D. | Linear motion in the x̂ direction. |
| Answer» B. Circular motion in the xy-plane. | |
| 31. |
According to Ampere's circuital Law The Line Integral of H about any closed path is exactly_______ to the direct current enclosed by that path. |
| A. | equal |
| B. | 4 times |
| C. | double |
| D. | half |
| Answer» B. 4 times | |
| 32. |
In an a.c. electric motor, the direction of current in the coil changes once in every: |
| A. | two rotations of the coil |
| B. | one rotation of the coil |
| C. | half rotation of the coil |
| D. | one-fourth rotation of the coil |
| Answer» D. one-fourth rotation of the coil | |
| 33. |
In order to produce a flux of 100 μwb in an air gap of length 0.2 mm and area of cross-section is 1 cm2, the MMF required is: |
| A. | 500/π |
| B. | 500 π |
| C. | 250 π |
| D. | 250/π |
| Answer» B. 500 π | |
| 34. |
Directions: It consists of two statements, one labelled as the 'Statement (I)' and the other as 'Statement (II)'. Examine these two statements carefully and select the answer using the codes given below:Statement (I): Ferrite cored coils are used in high frequency tuned circuits.Statement (II): Ferrite cored coils have high Q as compared to iron-cored coils. |
| A. | Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) |
| B. | Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) |
| C. | Statement (I) is true but Statement (II) is false |
| D. | Statement (I) is false but Statement (II) is true |
| Answer» B. Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) | |
| 35. |
Choose the correct relation between magnetic flux density (B) and magnetic field strength (H) in a material with absolute permeability as μ. |
| A. | B = μH |
| B. | \(B = \frac{\mu }{H}\) |
| C. | B = μ + H |
| D. | \(B = \frac{H}{\mu }\) |
| Answer» B. \(B = \frac{\mu }{H}\) | |
| 36. |
A conductor 0.2 m long is carrying a current of 20 A at right angles to a magnetic field of 0.5 Tesla. What will be force on the conductor of the current is increased by 50 percent? |
| A. | 1 N |
| B. | 4 N |
| C. | 6 N |
| D. | 3 N |
| Answer» E. | |
| 37. |
Magnetic field strength at a point distant r metres from a pole is: |
| A. | directly proportional to square of the r3 |
| B. | directly proportional to square of the r2 |
| C. | directly proportional to square of the r |
| D. | inversely proportional to square of the r |
| Answer» E. | |
| 38. |
Calculate the flux density at a distance of 5 cm from a long straight circular conductor carrying a current of 250 A and placed in air. |
| A. | 102 Wb/m2 |
| B. | 10-2 Wb/m2 |
| C. | 10-3 Wb/m2 |
| D. | 103 Wb/m2 |
| Answer» D. 103 Wb/m2 | |
| 39. |
Flux density is quantified in terms of: |
| A. | Wb-m |
| B. | Wb |
| C. | Wb-m2 |
| D. | Wb / m2 |
| Answer» E. | |
| 40. |
An air core toroid with 500 turns having a cross section area of 6 cm2 and a mean radius of 15 cm is carrying a current of 5 A. What is the magnetic flux density at the mean radius? |
| A. | 2653 T |
| B. | 1/300 T |
| C. | 2123 T |
| D. | 1/400 T |
| Answer» C. 2123 T | |
| 41. |
A flux 1.2 mWb exerts in a magnet having a cross-section of 30 cm2. The flux density in tesla is |
| A. | 4 |
| B. | 0.4 |
| C. | 2.5 |
| D. | 40 |
| Answer» C. 2.5 | |
| 42. |
A region shown below contains a perfect conducting half-space and air. The surface current \(\overrightarrow {{K_S}} \) on the surface of the perfect conductor is \(\overrightarrow {{K_S}} = \hat x2\) amperes per meter. The tangential \(\vec H_t\) field in the air just above the perfect conductor is |
| A. | (x̂ + ẑ) 2 amperes per meter |
| B. | x̂ 2 amperes per meter |
| C. | –ẑ 2 amperes per meter |
| D. | ẑ 2 amperes per meter |
| Answer» E. | |
| 43. |
A current of 5 A passes along the axis of a cylinder of 5 cm radius. The flux density at the surface of the cylinder is |
| A. | 2 μT |
| B. | 20 μT |
| C. | 200 μT |
| D. | 2000 μT |
| Answer» C. 200 μT | |
| 44. |
Magnetic field strength is quantified in terms of: |
| A. | N/Wb |
| B. | Am |
| C. | Wb |
| D. | Nm |
| Answer» B. Am | |
| 45. |
Assuming that each loop is stationary and time varying magnetic filed B̅, induces current I, which of the configuration in the figure are correct? |
| A. | 1, 2, 3 and 4 |
| B. | 1 and 3 only |
| C. | 2 and 4 only |
| D. | 3 and 4 only |
| Answer» D. 3 and 4 only | |