Answer:

Degaussing in a picture tube means removing residual magnetism in mask, shield, etc.

Degaussing is a process used to remove or neutralize any residual magnetism in a picture tube. This residual magnetism can cause color distortion or other image quality issues. Degaussing ensures that the picture tube is in a neutral magnetic state, allowing for accurate and consistent image reproduction.

Explanation:

Degaussing is achieved by using a degaussing coil, which is typically built into the picture tube or the monitor. When the monitor is turned on, the degaussing coil is briefly energized, producing a strong alternating magnetic field around the tube.

The process of degaussing can be explained in the following steps:

1. Residual Magnetism: Picture tubes, especially cathode-ray tubes (CRTs), can develop residual magnetism due to the presence of magnetic fields from external sources or materials used in the construction of the tube itself. This residual magnetism can interfere with the proper functioning of the electron beam, leading to image distortion.

2. Degaussing Coil: The degaussing coil is a specially wound coil of wire that is positioned around the picture tube. It is designed to produce a strong alternating magnetic field when energized.

3. Alternating Magnetic Field: When the monitor is turned on, a current is passed through the degaussing coil, creating an alternating magnetic field. This field varies rapidly in strength and direction.

4. Neutralizing Residual Magnetism: The alternating magnetic field generated by the degaussing coil interacts with the residual magnetism in the picture tube. The changing magnetic field induces eddy currents in the metallic parts of the tube, including the mask, the shadow mask, and the shield. These eddy currents, in turn, generate their own magnetic fields. The interaction between the alternating magnetic field and the induced magnetic fields cancels out the residual magnetism, effectively neutralizing it.

5. Result: By neutralizing the residual magnetism, the degaussing process ensures that the picture tube is in a magnetically neutral state. This allows for accurate and consistent image reproduction, without any color distortion or other image quality issues caused by residual magnetism.

Conclusion:

The correct answer, option B, states that degaussing in a picture tube means removing residual magnetism in the mask, shield, etc. This process is achieved by using a degaussing coil to generate an alternating magnetic field that neutralizes the residual magnetism and ensures accurate image reproduction.