How do electric or magnetic fields deflect an electron beam in a cathode-ray tube?

In a cathode-ray tube (CRT), the electron beam is deflected primarily through the use of electromagnetic fields to scan the screen and create images.12

Magnetic Deflection

Scanning is typically achieved using a deflection yoke, which contains two sets of electromagnetic coils positioned around the neck of the tube. When an electron moves through a magnetic field, it experiences a force perpendicular to both its direction of motion and the magnetic lines of force. By passing the magnetic field through the tube neck at right angles to the beam, the system exerts a force that changes the beam's direction. The magnitude of this deflection is proportional to the current flowing through the coils, allowing for precise control of the beam's position on the screen.1

Electric Fields

While magnetic deflection is standard for television picture tubes, the controlled deflection of a cathode ray by electric or magnetic fields is a fundamental principle used in devices like the cathode-ray oscilloscope to monitor voltage and current variations. In these systems, electric fields can also be employed to steer the beam by exerting electrostatic forces on the charged electrons.2