MCQs on Electromagnetism - 1

1. A free electron mean
(a) All the electron in an atom
(b) The electrons not belongs to the atom itself
(c) Valance electrons which are loosely attached to the nucleus
(d)  All the above


2. When a potential difference applied to a resistor, the heat is produced by
(a) Due to the collision of free electrons with the molecules or atoms of the resistor
(b) Power dissipation
(c) Speed of response
(d) None of the above



3. On application of heat on electrolyte is exhibit
(a) Positive temperature coefficient
(b) No change in its resistance
(c) Resistance will increase
(d) Negative temperature coefficient


4. A wire of resistance R ohm stretched to double its length, then its resistance become
(a) R/4
(b) R/2
(c) 2R
(d) 4R


5. Two parallel wires carrying current in opposite direction
(a) Attracts each other
(b) Repel each other
(c) Cancel each other
(d) None of the above


6. The inductive reactants of an inductor in a DC circuit is
(a) 2nfL
(b) Zero
(c) wL
(d) m


7. The most efficient damping employed in electrical instrument is
(a) Air friction
(b) Fluid friction
(c) Eddy current
(d) None of the above


8. In thermocouple ammeter, the heat produced is proportional to
(a) Current
(b) Square root of current
(c) Square of current
(d) Voltage


9. The relation between the excitation current and magnetic flux of a transformer is
(a) Current leads flux
(b) Flux leads the current
(c) They are in phase
(d) None of the above



10. The equivalent resistance and leakage reactance of  a transformer can be found out by
(a) Open circuit test
(b) Short circuit test
(c) Polarity test
(d) None of the above


11. An electrical machine with lower efficiency will have
(a) Less losses
(b) More losses
(c) No losses
(d) Low operating cost


12.If the armature coil of DC machine is N turns then number of conductors of any coil side
(a) 2N
(b) N/2
(c) N2
(d) N


13. A moving iron instrument can measure
(a) AC
(b) AC & DC
(c) DC
(d) Pulse


14. The heat produced by an electric heating element is according to
(a) Ohm’s law
(b) Stefan’s law
(c) Faraday’s law
(d) Snell’s law


15. High frequency capacitance heating method is employed for heating
(a) Plastic
(b) Wood
(c) Dehydration of food
(d) All the above



16. In carbon arc welding, the carbon electrode with respect to work is
(a) Negative
(b) Positive
(c) As positive or negative
(d) None of the above


17.  Which lamp has the highest luminous efficiency?
(a) Filament
(b) Neon
(c) Mercury vapor
(d) Sodium vapor


18. The armature core of a DC machine is laminated to minimize
(a) Hysteresis loss
(b) Eddy current loss
(c) Mechanical loss
(d) Temperature loss


19. The cheapest shielding material used in Nuclear plant is
(a) Concrete
(b) Brick
(c) Boron
(d) Cadmium


20. At microwave frequencies, the size of the antenna becomes
(a) Very large
(b) Large
(c) Small
(d) Very small

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