Radar is the use of radio waves to determine the location of the object radio equipment, the current radar electromagnetic waves emitted by the frequency of more in the range of 200MHz to 1000MHz

(1) A. According to λ=< tr>

c

f

, the wavelength of electromagnetic waves in the frequency range of 200MHz to 1000MHz ranges from 0.3m to 1.5m, so A is correct.

B, according to electromagnetic field theory, changing electric field produces magnetic field, changing magnetic field produces electric field, so B is wrong.

C, measured from the launch of electromagnetic waves to receive the reflected wave time interval can determine the distance between the radar and the target as: x=

1

2

ct, so C is correct;

D, radar is the use of electromagnetic wave reflection principle, the shorter the wavelength of the electromagnetic wave, the less likely to diffraction, the better the reflection performance, so D is correct.

The choice of ACD.

(2) by ab is equal to bc can be seen, the electromagnetic wave from the launch to return to the time used for 50?μs. Set the distance between the radar and the obstacle for x, the electromagnetic wave round trip time for t = 50?μs

2x = ct by

x=

1

2

ct=< table cellpadding="-1" cellspacing="-1" style="margin-right:1px">12 x 3.0 x 108 x 50 x 10-6 x m = 7.5 x 103?m.

Answer: the distance between the obstacle and the radar is 7.5 x 103m.