使用示波器做實驗與到的一些問題

There are static charges on your body, your skin, fingers and clothes that would give a small but unsteady voltage, detectable by the CRO.

When you touch the cables with two hands, the CRO tends to measure the potential difference between the two inputs (i.e. the p.d. across the two cables), which is practically very small as there should be no steady voltage across your body. Thus the signal is reduced.