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| Engineering Reviewer - Electricity and Magnetism Fundamentals |
Electricity and Magnetism Fundamentals
151. How is mutual inductance between two coils decreased?
A. By using a common core
B. By moving the coils closer
C. By moving the coils apart
D. By increasing the number of turns of either coil
152. A magnetic field is
A. The current flow through space around a permanent magnet
B. The force set up when current flows through a conductor
C. The force that drives current through a resistor
D. The force between the plates of a charged capacitor
153. Ohm’s law can be used only to a _____ circuit or component.
A. Unilateral
B. Exponential
C. Trivalent
D. Linear
154. When the current flows, the magnetic field ……. conductor is in what direction?
A. The same as the current direction
B. Opposite the current direction
C. Omnidirectional
D. In the direction determined by the left hand rule
155. The magnetic field around the conductor is determined by the
A. Size of the conductor
B. Amount of current
C. Current divided by the resistance
D. Resistance divided by the current
156. Back emf refers to the
A. Current equal to the applied emf
B. Opposing emf
C. Current opposing the applied emf
D. Voltage opposing the applied emf
157. The magnetic flux through a coil changes. This results to the induced emf acting in a direction as to
A. Oppose the change
B. Aid the change
C. Either oppose or aid the change
D. Neither oppose nor aid the change
158. A magnetic flux of 2.5 x10^4 Wb through an area of 5 x10^4 square meters results in
A. 5 Wb
B. 0.5 Tesia of flux density
C. 5x 10^-5 Wb of flux
D. 5000 Tesia of flux density
159. If a 20 V potential is applied across a relay coil with 50 turns having 1 Ω of resistance, the total magnetomotive producing magnetic flux in the circuit is
A. 10 Wb
B. 50 T
C. 1000 A t/m
D. 1000 A.t
160. What is the reluctance of a magnetic path having a length of 2x 10^-3m and cross- sectional area of 2.5 x 10^-3 m^2?
A. 6366 A.t/Wb
B. 6000 A.t/Wb
C. 8x10^-3 A.t/Wb
D. 0.8 A.t/Wb
161. Calculate the permeability (in T/A. t/m) of a magnetic material that has a relative permeability of 300
A. 3.78 x 10^-4
B. 3.78 x 10^-5
C. 3.78 x 10^-3
D. 3.78 x 10^-6
162. Calculate the flux density that will be produced by the field intensity of 2000 a. t/m for a permeability of 126 x 10^-6 T/A.t/m
A. 0.252 G
B. 0.252 x 10^-2 T
C. 0.252 T
D. 0.252 x 10^-2 G
163. How many turns are needed to produce a magnetomotive force of 1000 A.t for a coil with 6 amperes?
A. 6000 turns
B. 600 turns
C. 167 turns
D. 67 turns
164. A 6- V battery is connected across a solenoid of 100 turns having a resistance of 2 Ω, Calculate the number of ampere turns?
A. 100
B. 50
C. 300
D. 600
165. What determines the atomic number of an element?
A. The number of protons
B. The number of electrons
C. The number of neutrons
D. The number of neutrons and protons
166. One of the solid structures in which the position of the atoms or ions are predetermined
A. Crystalline solid
B. Amorphous solid
C. Polycrystalline solid
D. Poly- amorphous solid
167. Mmf in a magnetic circuit corresponds to _____ in an electric circuit
A. Emf
B. Voltage drop
C. Electric Field Intensity
D. Potential gradient
168. What solid has no defined crystal structure except perhaps in the arrangement of the nearest neighboring atoms or ions?
A. Crystalline
B. Amorphous
C. Polycrystalline
D. Poly- amorphous
169. Amorphous solid is also called
A. Crystalline
B. Non- crystalline
C. Polycrystalline
D. Homogenous
170. A principle that states that only two electrons with different spins are allowed to exist in a given orbit
A. Bohr’s principle
B. Pauli exclusion principle
C. Avogadro’s principle
D. Coulomb’s principle
171. What bond is formed when one or more electrons in the outermost energy orbit of an atom are transferred to another?
A. Ionic
B. Covalent
C. Metallic
D. Van der Waals
172. In electro-mechanical conversion devices like generators and motors the reason why a small air gap is left between the rotor and stator is to
A. permit mechanical clearance
B. increase flux density in air gap
C. decrease the reluctance of magnetic path
D. complete the magnetic path
173. What bond is formed when electrons in the outermost energy orbits of the atoms are shared between two or more electrons?
A. Ionic
B. Covalent
C. Metallic
D. Van der Waals
174. Why is it that the magnitude of magnetomotive force required for air gap is much greater than that required for iron part of a magnetic circuit?
A. Because air is a gas
B. Because air has the highest relative permeability
C. Because air is a conductor of magnetic flux
D. Because air has the lowest relative permeability
175. What type of bond is formed when there exists some form of collective interactions between the (negatively charged) electrons and (positively charged) nuclei in a solid?
A. Ionic
B. Covalent
C. Metallic
D. Van der Waals
176. Permeance of a magnetic circuit is _________ the cross-sectional area of the circuit.
A. directly proportional to
B. inversely proportional to
C. dependent of
D. independent of
177. Formed when there exist distant electronic interactions between (opposite) charges present in the neighboring atoms or molecules.
A. Ionic bond
B. Covalent bond
C. Metallic bond
D. Van der Waals bond
178. Defined as the ratio of the volume occupied by the atoms or ions in a unit cell divided by the volume of the unit cell and is used to measure the compactness of a crystal.
A. Atomic packing factor (APF)
B. Ionic Packing Ratio (IPR)
C. Atomic compacting factor (ACF)
D. Ionic compacting ratio (ICR)
179. A factor used to correct for the electrostatic forces of the more distant ions in an ionic solid.
A. Avogadro’s number
B. Planck’s constant
C. Boltzmann’s constant
D. Madelung constant
180. The conduction of electricity across the surface of a dielectric is called
A. creepage
B. skin effect
C. surface effect
D. crosstalk
181. A magnetic circuit carries a flux φi in the iron part and a flux φg in the air gap. What is the leakage coefficient?
A. φi/ φg
B. φi × φg
C. φg /φi
D. φi + φg
182. A law stating that the magnetic susceptibilities of most paramagnetic substances are inversely proportional to their absolute temperatures.
A. Curie’s Law
B. Child’s Law
C. CR Law
D. Curie-Weiss Law
183. The reluctance of the magnetic circuit is ________ relative permeability of the material comprising the circuit.
A. directly proportional to
B. inversely proportional to
C. independent of
D. dependent of
184. 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.
A. Curie’s Law
B. Child’s Law
C. CR Law
D. Curie-Weiss Law
185. 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.
A. Ewing’s theory of ferromagnetism
B. Oersted’s ferromagnetism theory
C. Maxwell’s magnetic theory
D. Ampere’s circuital law
186. The reluctance of a magnetic circuit varies with
A. length × area
B. area ÷ length
C. length ÷ area
D. length + area
187. 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.
A. Joule’s law
B. Faraday’s law
C. Volta’s theorem
D. Ampere’s theorem
188. What is the usual value of leakage coefficient for electrical machines?
A. 0.5 to 1
B. 1 to 5
C. 5 to 10
D. 1.15 to 1.25
189. The science of adapting electronics to aerospace flight.
A. Avionics
B. Aerotronics
C. Aerodynamics
D. Astrionics
190. The reluctance of a magnetic circuit is not dependent on which of the following?
A. Number of turns of coil
B. Magnetomotive force
C. Flux density in the circuit
D. Current in the coil
191. Another term for corona discharge.
A. Lightning
B. Sparking
C. Aurora
D. Corona Effect
192. The B-H curve for ________ is a straight line passing through the origin.
A. cobalt
B. air
C. hardened steel
D. soft iron
193. 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.
A. Bridgman effect
B. Corona effect
C. Dember effect
D. Destriau effect
194. The B-H curve of ________ is not a straight line.
A. air
B. wood
C. silicon steel
D. soft iron
195. If a magnetic flux cuts across 200 turns at a rate of 2Wb/s, the induced voltage according to Faraday’s law is about
A. 400 V
B. 100 V
C. 200 V
D. 600 V
196. What is the SI unit of reluctance?
A. At
B. At/m
C. N/Wb
D. At/Wb
197. A magnetizing force of 1000 AT/m will produce a flux density of __________ in air.
A. 1.257 mWb/m^2
B. 0.63 Wb/m^2
C. 1.257 Wb/m^2
D. 0.63 mWb/m^2
198. Hysteresis loss can be reduced by one of the following.
A. Increasing mmf of the circuit
B. Using material narrow hysteresis loop
C. Using ferromagnetic core
D. Laminating the magnetic circuit
199. The core of a transformer heats up when its primary is fed from an ac source because of
A. permeability
B. ferromagnetism
C. reluctance of core
D. hysteresis loss
200. Which of the following materials has the least hysteresis loop area?
A. soft iron
B. silicon steel
C. hard steel
D. wrought iron
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