Comparison between Electrostatic and Magnetic Deflection in a CRO

A cathode ray tube may apply two types of deflection on the electron beam. These are the electrostatic deflection and the magnetic deflection. Here we will discuss the different points of the comparison between two deflection methods.

Methods

The electrostatic deflection method uses an electric field to produce the deflection of the electron beam. Here we apply a potential difference between two horizontally placed parallel plates. Therefore, the electron beam deflects  when it travels through this electric field means the space between the two horizontal plates.

On the other hand, the magnetic deflection method uses current carrying coils to produce the magnetic field. When the electron beam travels through the magnetic field it experiences the Lorentz Force to get diverted.

Relation with Accelerating Voltage

In electrostatic deflection the amplitude of the deflection is directly proportional to the acceleration voltage of the electron beam.

In magnetic deflection the amplitude of the deflection is directly proportional to the square root of the accelerating voltage of the electron beam.

Size of Electron Beam

The size of the beam for a given accelerating voltage is quite small in the electrostatic deflection than that of the magnetic deflection. Practically, in the magnetic deflection the size of the beam is quite large and wide.

Sensitivity

The sensitivity of the electrostatic deflection is inversely proportional to the accelerating voltage. Whereas the sensitivity of the magnetic deflection is inversely proportional to the square root of accelerating voltage.

Size of Cathode Ray Tube

The electrostatic method of deflection requires a lengthy tube. Besides, the magnetic method of deflection requires a shorter tube.

Brightness

The brightness of the display of a cathode ray tube for the electrostatic deflection is quite lower than that of the magnetic deflection. That means the magnetic deflection producers much brighter display.

Applications

We use the electrostatic deflection in a cathode ray oscilloscope mainly for observing the behaviour of waveforms of different electrical signals. Therefore in the medical applications and in experimental Laboratories the applications of this type of CRO are maximum.

On the other hand, the picture tube of televisions and similar devices use the magnetic deflection for the purpose displaying images.

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