QUESTION 24 1 po A solenoid consists of O a burglar alarm relay O two plates sep

Question

QUESTION 24 1 po A solenoid consists of O a burglar alarm relay O two plates separated by an insulator O a permanent magnet O a coil of wire wound around a core QUESTION 25 1 p The movable part of the relay is the: O the armature. O electromagnetic coil. O magnetic field. O all of these. Question Completion Status: QUESTION 26 Increasing the speed at which a magnet moves through a coil of wire causes the induced voltage to O decrease O remain the same O increase QUESTION 27 Electromagnetic induction is best defined as the process by which a voltage is produced in a conductor when there is: O energy produced by the rotating coils. O motion around the magnetic felds. O motion between the magnetic poles. O motion between the conductor and the magnetic field. QUESTION 28 A strong magnetic field around a conductor indicates a small current flowing through the conductor. O True O False QUESTION 29 If a relay picks up and makes a contact but does not stay picked up, what's the trouble? O The magnetic field is too strong. O The relay coil is open. O The magnetic field is too weak. O There is no trouble. The relay is operating normally. QUESTION 30 An ampere-turn is a unit of O magnetomotive force (mmf) O resistance O reactance QUESTION 31 Aluminum, brass, and iron make good magnets. O True O False QUESTION 32

Explanation / Answer

24. A solenoid consists of a coil of wire wound around a core.

25. The movable part of the relay is called armature.

26. In general, E= BLVsin where E is induced e.m.f, B is magnetic field density, V is the linear velocity between field and the conductor. Thereforeas the speed increases, induced emf also increase.

27. Farady's Law of electromagnetic induction states that any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil. Thiis is possible only in there is relative motion between a magnetic field and the conductor.

28. False. More the current, more will be the mmf and hence stronger will be the magnetic field.

29. Magnetic field is weak. It should be strong enough to keep attracting the armature of the relay.

30. MMF. = NI where N is the number of turns in the coil and I is the electric current through the circuit.

31. True. They offer least reluctance and high permeability. Also their hysterisis loops are thinner comparitively.

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