【判断题】From , it can be seen that for ζ >0.707, there is no resonant peak. The magnitude decreases monotonically with increasing frequency ζ . The magnitude is greater than 0 dB for all values of .
【单选题】An open pipe of air supports standing waves at frequencies of 300 Hz and 400 Hz. There are no other frequencies between these two. What is the frequency of the second harmonic of this tube?
【简答题】In the former case the audio-frequency signal from the microphone, with little or no amplification, is used to modulate the output of the oscillator, and the modulated carrier frequency is then amplif...