一、选择题1.下列关于电磁波的说法中正确的是A.麦克斯韦电磁场理论预言了电磁波的存在B.电磁波从真空传入水中时,波长将变长C.雷达是利用自身发射的电磁波来对目标进行定位的D.医院中用于检查病情的“B超”,利用了电磁波的反射原理2.日光灯电路主要由镇流器、启动器和灯管组成 First, multiple-choice questions 1. The following statements about electromagnetic waves are correct. A. Maxwell’s electromagnetic field theory predicts the existence of electromagnetic waves. B. When electromagnetic waves pass from the vacuum into the water, the wavelength will become longer. C. The radar uses the electromagnetic waves emitted by itself to The target is positioned D. The “B-ultrasound” used to check the condition in the hospital uses the reflection principle of the electromagnetic wave. 2. The fluorescent lamp circuit is mainly composed of a ballast, a starter and a lamp tube.