單項(xiàng)選擇題Which of the motors for the devices listed below is fitted with an instantaneous overload relay?（）

A.Fan
B.Pump
C.Winch
D.Machine tool


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1.單項(xiàng)選擇題One factor that determines the frequency of an alternator is the（）.

A.number of turns of wire in the armature coil
B.number of magnetic poles
C.strength of the magnets used
D.output voltage

2.單項(xiàng)選擇題The device that most commonly utilizes the principle of electromagnetic induction is the（）.

A.diode
B.transformer
C.transistor
D.rheostat

3.單項(xiàng)選擇題Which of the listed devices is used to measure pressure and convert it to an electrical signal?（）

A.Transducer
B.Reducer
C.Transformer
D.Rectifier

4.單項(xiàng)選擇題A direct current passing through a wire coiled around a soft iron core is the description of a simple（）.

A.magnetic shield
B.electromagnet
C.piezoelectric device
D.electromagnetic domain

5.單項(xiàng)選擇題Which of the following electric motors would be the safest and most reliable to use on the main deck of a vessel in foul weather conditions?（）

A.Sealed motors
B.Drip proof motors
C.Enclosed motors
D.Watertight motors