CRO Phosphor Explained
The screen of a Cathode Ray Oscilloscope (CRO) is coated with a fluorescent material, often called a phosphor. When the high-energy electron beam strikes this phosphor coating, it excites the material, causing it to emit visible light. The color of the light produced depends on the specific chemical composition of the phosphor.
Phosphor Glow Color Determination
Different phosphors and impurities produce distinct colors:
- Pure Zinc Sulfide (ZnS): Emits primarily in the ultraviolet range, not typically visible.
- Zinc Sulfide with Copper impurity (ZnS:Cu): Known to produce a green or yellowish-green glow.
- Zinc Sulfide with Silver impurity (ZnS:Ag): This specific combination is well-known for emitting a blue or bluish-violet light when bombarded by electrons.
- Yttrium Oxide: While used in some display technologies, it's not the standard material for producing a bluish glow on a basic CRO screen.
Identifying the Bluish Glow Material
Based on the properties of common CRO phosphors, Zinc Sulfide with silver as an impurity is the material that yields the characteristic bluish glow on the viewing surface.
Important Questions from Cathode Ray Oscilloscope
The function of a trigger level knob on a CRO is:
Aquadag coating is most commonly used in CROs to:
CRO stands for:
Calculate the maximum velocity of the beam of electrons in a CRT having a cathode and anode voltage of 182 V. Assume that the electrons leave the cathode with zero velocity. (Charge of electron = 1.6 × 10-19 C and mass of electron = 9.1 × 10-31 kg)
Which of the following expression is the correct formulae for the deflection sensitivity ‘S’ of a CRT, if
D = deflection on the fluorescent screen
L = distance from the center of the deflection plates to the screen
Ld = effective length of the deflection plates
d = distances between the deflection plates
Ed = Potential between deflecting plates
Ea = accelerating voltage
