Practice Test (See related pages) 1 For an electromagnet, the strength and intensity of the magnetic field depends on current flow and number of coil turns in a given length. A) True B) False 2 The mmf of a coil is inversely proportional to both the current and the number of turns. A) True B) False 3 The SI abbreviation for ampere-turn is I-T. A) True B) False 4 The cgs unit for field intensity is the oersted. A) True B) False 5 The permeability of a material is similar in many respects to the resistance in electric circuits. A) True B) False 6 The effect of little change in flux density, when the field intensity increases, is called saturation. A) True B) False 7 Reducing the residual induction is a method of demagnetization called degaussing. A) True B) False 8 When the magnetic lines of two fields are in the same direction, the lines of force oppose each other, making the field weaker. A) True B) False 9 A coil of wire with more than one turn is generally called a solenoid. A) True B) False 10 When magnetic flux moves, the motion of magnetic lines cutting across a conductor forces free electrons in the conductor to move and produce current by an action called . 11 The symbol generally used for rate of change is . 12 The minimum amount of relay coil voltage necessary to energize or operate a relay is called voltage. 13 Reducing the residual induction is a method of called degaussing. 14 An effect of a in producing rotation is called torque. 15 A relay is an device that operates switching contacts by electromagnetic induction. 16 The movable of an electromechanical relay is called the armature. 17 Relay contacts may if they are dirty. 18 The physical motion form the forces of magnetic fields is called A) magnetic motion B) emf C) generation action D) motor action 19 Whose law or theorem is the basic principle for determining the direction of an induced voltage or current? A) Maxwell B) Gilbert C) Lenz D) Oersted 20 In what device is motion supplied so that the flux and conductor can cut across each other to induce voltage across the ends of the conductor? A) motor B) generator C) relay D) solenoid 21 The mmf of a coil is A) inversely proportional to the current and number of turns B) directly proportional to the current and number of turns C) inversely proportional to the current D) inversely proportional to the number of turns 22 The cgs unit of magnetomotive force is the A) gilbert B) maxwell C) oersted D) joule 23 The effect of little change in flux density when the field intensity increases is called A) reactance B) reluctance C) saturation D) induction 24 Hysteresis means A) magnetize below B) leading ahead C) lagging behind D) moving over 25 Energy wasted in heat as the molecular dipoles lag the magnetizing force is called the A) copper loss B) IR loss C) skin effect D) hysteresis loss
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