27 real Electrical Materials & Safety Basics questions from the Electrical Core bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is Copper vs aluminium conductors?
Junior
A.zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
B.copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
C.cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
D.maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
2. Which term means: "copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines"?
A.Copper vs aluminium conductors — maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
B.Copper vs aluminium conductors — about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people
C.Copper vs aluminium conductors — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
D.Copper vs aluminium conductors — copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
A.classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
B.copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
C.cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
D.zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
A.Insulation thermal classes — copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
B.Insulation thermal classes — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
C.Insulation thermal classes — maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
D.Insulation thermal classes — soft materials have narrow hysteresis loops for cores; hard materials have wide loops and high coercivity for permanent magnets
A.Dielectric strength — maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
B.Dielectric strength — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
C.Dielectric strength — zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
D.Dielectric strength — risk of fatal heart fibrillation rises sharply for currents above roughly 30–50 mA through the chest lasting more than a few hundred milliseconds
A.cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
B.pentavalent donors produce n-type and trivalent acceptors produce p-type material, shifting the Fermi level toward the respective band
C.copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
D.about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people
11. Which term means: "pentavalent donors produce n-type and trivalent acceptors produce p-type material, shifting the Fermi level toward the respective band"?
A.Semiconductor doping — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
B.Semiconductor doping — pentavalent donors produce n-type and trivalent acceptors produce p-type material, shifting the Fermi level toward the respective band
C.Semiconductor doping — zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
D.Semiconductor doping — cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
14. Which term means: "about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people"?
A.Let-go current — maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
B.Let-go current — copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
C.Let-go current — about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people
D.Let-go current — risk of fatal heart fibrillation rises sharply for currents above roughly 30–50 mA through the chest lasting more than a few hundred milliseconds
17. Which term means: "cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses"?
A.CRGO silicon steel — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
B.CRGO silicon steel — about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people
C.CRGO silicon steel — zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
D.CRGO silicon steel — cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
20. Which term means: "soft materials have narrow hysteresis loops for cores; hard materials have wide loops and high coercivity for permanent magnets"?
A.Soft vs hard magnetic materials — pentavalent donors produce n-type and trivalent acceptors produce p-type material, shifting the Fermi level toward the respective band
B.Soft vs hard magnetic materials — copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
C.Soft vs hard magnetic materials — maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
D.Soft vs hard magnetic materials — soft materials have narrow hysteresis loops for cores; hard materials have wide loops and high coercivity for permanent magnets
A.Superconductivity — zero resistance below a critical temperature, lost when the critical magnetic field or critical current density is exceeded
B.Superconductivity — soft materials have narrow hysteresis loops for cores; hard materials have wide loops and high coercivity for permanent magnets
C.Superconductivity — pentavalent donors produce n-type and trivalent acceptors produce p-type material, shifting the Fermi level toward the respective band
D.Superconductivity — cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
A.risk of fatal heart fibrillation rises sharply for currents above roughly 30–50 mA through the chest lasting more than a few hundred milliseconds
B.maximum electric field an insulating material withstands before breakdown, about 3 kV/mm for air at atmospheric pressure
C.cold-rolled grain-oriented steel with about 3% silicon in 0.23–0.35 mm laminations, used in transformer cores to cut hysteresis and eddy losses
D.copper (resistivity 1.72 µΩ·cm) is preferred for windings; aluminium has about 60% of its conductivity but one-third the weight, suiting overhead lines
26. Which term means: "risk of fatal heart fibrillation rises sharply for currents above roughly 30–50 mA through the chest lasting more than a few hundred milliseconds"?
A.Ventricular fibrillation threshold — about 10 mA at 50 Hz is the threshold above which a person cannot release a gripped conductor, which is why 30 mA RCDs protect people
B.Ventricular fibrillation threshold — risk of fatal heart fibrillation rises sharply for currents above roughly 30–50 mA through the chest lasting more than a few hundred milliseconds
C.Ventricular fibrillation threshold — soft materials have narrow hysteresis loops for cores; hard materials have wide loops and high coercivity for permanent magnets
D.Ventricular fibrillation threshold — classes A (105 °C), B (130 °C), F (155 °C) and H (180 °C) fix the maximum permitted winding temperature
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