Question

Cathode Ray Oscilloscope uses the principle of

• A. Electronic focusing
• B. Electromagnetic focusing
• C. Electrostatic focusing
• D. Electromechanical focusing

Hint:

To remember: CROs use Static fields (Electrostatic) for both focusing and deflection because they are easier to control precisely at high frequencies compared to magnetic fields.

Answer 1

The Correct Option is C

The Cathode Ray Oscilloscope (CRO) relies on a Cathode Ray Tube (CRT) to visualize electrical signals. A key part of this process is ensuring the electron beam is focused into a sharp point on the phosphor screen. 1. The Focusing Mechanism: In standard lab oscilloscopes, the focusing is achieved through an "electron lens" system. This system consists of several cylindrical anodes held at different high-voltage potentials.

2. Electrostatic Principle: The electric fields created between these anodes exert forces on the moving electrons, bending their paths in a manner analogous to how an optical lens bends light. This is called

Electrostatic focusing. It is preferred in CROs because it allows for compact designs and faster response times for signal measurement.

3. Distinguishing from other types:

• Electromagnetic focusing: Uses magnetic coils to focus the beam. This is commonly found in television tubes or electron microscopes rather than general-purpose laboratory CROs.

• Electromechanical focusing: Does not exist in the context of electron beam control; focusing is done by fields, not mechanical levers.