4. Electricty and magnetism
description
Transcript of 4. Electricty and magnetism
4. Electricty and magnetism
4.6 Cathode – ray oscilloscopes
(a) Cathode rays
4.6 Cathode-ray oscilloscopes
Thermionic emission
Thermionic emission
Thermionic emission
The Electron gun
What is an Electron Gun?
The electron gun structure
electron gun photograph
Electron energy
• Where: e = electron charge ( 1.6 x10-19 C) V = d.c voltage (cathode – anode)
Cathode rays propertiesThese rays originate from cathode. Cathode rays travel in straight line. Cathode rays carry negative charge. Cathode rays are deflected by electric field. Cathode rays are deflected by magnetic field. These rays consist of material particles. Cathode rays consist of "electron". Produce a shadow when obstructed by objects.Cathode rays can produce fluorescence.
Deflection tube
Magnetic deflection
4.6 (b) Simple treatment of cathode-ray oscilloscope
cathode ray oscilloscope
tube photograph
tube diagram
H.T. supply
heater supply
y plates x plates
+-
phosphor screen
anode
summary
H.T. supply
heater supply
y plates x plates
+-
phosphor screen
anode
electron gun produces a beam of
electrons light produced on the screen by electron beam
a p.d. across the y plates deflects the
trace vertically
a p.d. across the x plates deflects the trace horizontally
gain andf time-base controls
peak voltage
Peak p.d. = 3 Divisions x 1.0 mV/div = 3.0 mV
period & frequency
period = 4.0 divisions x 1.0 ms/div = 4.0 ms
frequency = 1 / periodfrequency = 1 / 0.004 sfrequency = 250 Hz
self test