Oscilloscope

An oscilloscope is a glass tube with an electron gun at one end and a fluorescent screen at the other.Electrons are emitted from a heated filament by thermionic emission. The electrons are then focused into a beam by two plates and accelerated through a hole in the plates. They then pass between two pairs of parallel plates (the X-plates and Y-plates) where they are deflected by an electric field.The beam hits a fluorescent screen.A spot of light is emitted where the beam hits the screen.The oscilloscope trace is formed by displacing the spot of light by deflecting with an electric field. The displacement of the spot of light is proportional to the applied p.d.The X plates are connected to the time base circuit.This makes the spot move from left to right across the screen at constant speed.The X scale is calibrated in milli or microseconds per cmThe Y scale is called the Y gain. The input p.d. is connected to the Y plates so moves the spot up and down to trace out the waveform.The Y gain is calibrated in volts per centimetre (Vcm^-1)