Charge to mass ratio 實驗問題

Q:請問6.3V supplies既作用係咩?

The 6.3v supply is used to deliver electric current to heat up the filament (電熱絲)(see fig 20-1), which in turn heat up the cathode (陰極). Electrons will be ejected from the hot cathode. Such phenomenon is called "thermionic emission".

Q:點解要用evacuated tube??

If the tube is not evacuated, there is air inside. Electrons would collide with air molecules inside the tube and rapidly lose (kinetic) energy. As such, almost all eelctrons would slow down and stopped before completing a circular path. Hence, no complete circle formed by the electron beam could be observed.