单项选择题
A.number of turns of wire in the armature coil
B.number of magnetic poles
C.strength of the magnets used
D.output voltage
单项选择题 The device that most commonly utilizes the principle of electromagnetic induction is the（）.
单项选择题 Which of the listed devices is used to measure pressure and convert it to an electrical signal?（）
单项选择题 A direct current passing through a wire coiled around a soft iron core is the description of a simple（）.