Cathode Rays

	Is the process of emission of electrons from a heated metal’s surface
Thermionic Emission	OR
	Is the discharge of electrons from the surfaces of heated materials

Electrons are emitted from the metal surface because the thermal energy given to the carrier overcomes the binding potential.

This binding potential also known as work function of the metal

  

FACTORS AFFECTING THE RATE OF THERMIONIC EMISSION

(i)      Work function of the metal

The lower the work function the greater the rate of emission of electrons from the surface.

(ii)    Temperature of the surface

The higher the temperature the high the rate of emission as the electrons will have more kinetic energy to leave the surface.

(iii)  Surface area of the metal

The Larger the surface area of the metal, the high rate of emission as thermionic emission

CATHODE RAYS

Are stream of fast – moving electrons.

OR

Are beam of electrons moving at high speed in vacuum.

The electrons move in a specific direction.

PROPERTIES OF CATHODE RAYS

        i.            They travel in straight lines from the negative pole (cathode).

       ii.            The produce fluorescence in the glass walls of the discharge tube.

     iii.            They possess heating effect.

     iv.            They can cause ionization in gases.

       v.            They consist of negatively charged particles.

     vi.            They produce X- rays when fall only certain metal such as copper.

   vii.            They can penetrate through thin metallic sheets.

 viii.            They are deflected when subjected to a strong magnetic field and electrical fields

CATHODE RAY TUBE

Cathode ray tube (CRT) is a vacuum tube containing an electron gun, with a source of electrons and fluorescent screen

Cathode ray tube nearly as the same as Cathode Ray Oscilloscope (CRO)

STRUCTURE OF CATHODE RAY OSCILLOSCOPE (CRO)

FUNCTIONS OF THE COMPONENTS OF THE CATHODE RAY OSCILLOSCOPE (CRO)

PART	COMPONENT	FUNCTION
Electron gun	(a)    Filament	When a current passes through the filament, the filament becomes hot and heats up the cathode.
	(b)   Cathode	Emit electrons when it is hot
	(c)    Control Grid	i.            Control the number of electrons reaching the fluorescent screen
		ii.            Control the brightness of the spot on the screen
	(d)   Focusing Anode	To focus the electrons onto the screen
	(e)   Accelerating Anode	To accelerate the electrons to high speed
Deflecting system	(a)    Y – Plates	To deflect the electron beam vertically
	(b)   X – Plates	To deflect the electron beam horizontally
Fluorescent screen	The screen is a glass surface coated with a fluorescent material (Zinc sulphide)	i.            The fluorescent material converts the kinetic energy of electrons to heat and light energy when the electron collides with the screen.
		ii.            Where images are displayed

APPLICATIONS OF CATHODE RAY OSCILLOSCOPE (CRO)

Cathode Ray Oscilloscope, CRO is used:

                                i.            To display waveform of waves

                               ii.            To measure the potential difference

                             iii.            To measure short time interval

                             iv.            To measure the frequency of oscillating signals