4.6.CATHODE RAY OSCILLOSCOPE Ambar Sarup

What is a Cathode Ray? A cathode ray is a beam of fast flowing electrons.

How are Cathode Rays Produced? Produced by heating a filament, also called a cathode When enough potential difference is applied to the filament, thermionic emission occurs with heat Emission of electrons by heating effect is called thermionic emission

Cathode Rays To produce Cathode Rays certain conditions are required: 1.Vacuum Tube 2.High potential between anode and cathode. A vacuum Cathode Ray filament anode

Properties of Cathode rays Produce a shadow, showing that the rays are travelling in a straight line. Electron flow Object Object Shadow

Deflected in a circular manner in a magnetic field Direction of motion given by Fleming's left hand rule. Motion Current Field

Deflected by an electric field Deflected towards the direction of the field (from negative to positive) Deflects toward the positive, away from the negative

Cathode Ray Oscilloscope

Parts of a Cathode Ray Oscilloscope Heated filament: To produce electrons by thermionic emission Grid: Perforated metal plate with negative potential difference It controls the amount of electrons reaching the screen. It is also a brightness control Anode: It attracts electrons passing through the grid, concentrates them into a fine beam and accelerates them onto the screen Screen: When fast moving electrons make Impact with screen, part of the thermal energy is converted into heat and the rest is absorbed by screen and reconverted into light.

Parts of a Cathode Ray Oscilloscope Deflection Plates Y-plates (horizontal plates) Move the beam vertically When connected to AC supply, the plates change polarity, causing a straight line to appear X-Plates (vertical plates) Move the beam horizontally When connected to a device called a timebase, changing voltage causes the dot to move from left to right

Beam deflected upward on screen Vertical deflection plate Y-Deflection Plates The electron beam is negative, thus the negative plate repels the beam and the positive plate attracts the beam

Deflected by electric field toward the positive plate and away from the negative plate Beam deflected downward

Beam deflected downward and upwards and due to AC - Y-Deflection Plates connected to Alternating Current A straight line appears because the deflection is very fast ~

Deflection to the left hand side X-Deflection Plates The electron beam is negative, thus the negative plate repels the beam and the positive plate attracts the beam

Deflection to the right hand side X-Deflection Plates The electron beam is negative, thus the negative plate repels the beam and the positive plate attracts the beam

X-Deflection Plates ~ Beam deflected left and right due to AC A straight line appears because the deflection is very fast

Timebase circuit Flyback Linear growth Pd The time base circuit produces an increasing pd which then cuts off at the flyback. Its function is to move the electron beam across the screen over a specific time. ( sweeps the screen). The time can be adjusted. The flyback prevents the dot from moving from right to left and so the dot reappears on the left side. t

Applications of a Cathode Ray Oscilloscope A voltmeter Timebase Ms/div V/div Gain control to change amplitude

As a voltmeter Y sets to 2v per div Displaced by 2 div p.d = 2 x 2 = 4 V

To measure time A B Sensitivity = 4 V/div Time base = 100 ms/div A B From CRO, Time between A and B = 4 div 4 div = 4 x 100 = 400 ms or 0.4s

To display wavefronts Time base = 50 ms/div Sensitivity = 3 v/div tBtB AC ~

Periodic time = 4 div = 4 x 50 T = 200 ms Frequency = ( 1 / (200 x )) = 5 Hz Amplitude of wave = 2 div = 2 x 3 = 6 V 2 divisions 4 divisions

What are Cathode Rays Used In? Old Televisions (Cathode Ray Tubes) X-Ray Tube (Cathode Ray Tubes) Radar and Sonar Monitors (Cathode Ray Oscilloscope) Hospital Heart Monitors (Cathode Ray Oscilloscope)

Sources images/MalteseCrossCRT2-1000x667.jpg images/MalteseCrossCRT2-1000x667.jpg content/uploads/2014/07/paddle2z.jpg content/uploads/2014/07/paddle2z.jpg content/uploads/2011/12/HappyFace.jpg images/CrookesTubes x667.jpg images/CrookesTubes x667.jpg pg pg Pople, Steven. Complete Physics for IGCSE