示波器的使用及声速的测量.ppt

示波器的使用Application of Oscilloscope The Lab center of physics Even rotation of the drum – even motion of the electron beam along the x-direction. Motion of the pen in y-direction – deviation of the beam in y-direction proportional to the measured voltage. A question: The electron beam moving along x-direction reaches the end of the screen at some point and has to jump back and start writing again from the beginning of the screen. How come that you normally only see one curve on the screen at any time?By the way, how fast does the beam go from left to right? The answer is triggering.After drawing one curve (sinusoidal, triangular, square…) on the screen the electron beam returns back to its starting point, but it does not start drawing another curve, before the voltage reaches some preset value – trigger level. Function generator 空气中声速的测量Measurement of Sound Velocity in Air The Lab center of physics Introduction Acoustics may be defined as the generation, transmission, and reception of energy in the form of vibrational waves in the matter. As the atoms or molecules of a fluid or solid are displaced from their normal configuration, an internal elastic restoring force arises. Examples including the tensile (张力) force produced when a spring is stretched. It is this elastic restoring force, coupled with inertia (惰性) of the system, that enables matter to participate (参与) in oscillatory vibrations and thereby generate and transmit acoustic waves. The most familiar acoustic phenomenon is that associated with of sound. For the average young person, a vibrational disturbance is interpreted as sound if its frequency lies in the range of about 20 to 20000Hz. However in a broader sense acoustic also includes the ultrasonic frequencies above 20000Hz and the infrasonic frequencies below 20Hz. The measurement of speed of sound is of interesting for understanding the main property of sound. One can easily obtain the velocity of sound through the following expression: Purpo