Trajectory of an electron in cathode ray tubes

In summary, when an electron travels under the influence of a magnetic field, it will move in a circular arc due to the perpendicular force exerted by the field. This is because the acceleration is normal to the velocity, causing only the direction of the velocity to change. However, when an electric field alone is applied, the electron will follow a parabolic path due to the force exerted by the electric field in the same direction as its motion. The force from a magnetic field is given by F=qVXB, while for an electric field alone it is F=qE.
  • #1
mattg443
12
0
Why is it that an electron traveling under the influence of a magnetic field (i.e electron going from left to right and B field going into the page) will travel in the arc of a circle

yet when an electric field alone is applied (say up page and the direction of motion of the electron is the same) the electron will travel in a parabolic path? when in both cases, a force is exerted on the electron is downwards?
 
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  • #2
The force the magnetic field exerts on a moving charged particle is perpendicular to both the magnetic field and the velocity of the particle. The acceleration is normal to the velocity: only the direction of the velocity changes, its magnitude does not. This is circular motion.
 
  • #3
mattg443 said:
yet when an electric field alone is applied (say up page and the direction of motion of the electron is the same) the electron will travel in a parabolic path? when in both cases, a force is exerted on the electron is downwards?

The force due to the magnetic field is not constantly downwards. It may initially be downwards, but as it changes the direction of the velocity, the force will also change direction; even though the magnetic field remains the same.

the force from a magnetic field is given by
F=qVXB (resulting in circular motion)

and for the electric field alone,
F=qE.

Bold letters are vectors. hope this helps!
 

1. What is a cathode ray tube (CRT)?

A cathode ray tube is a vacuum tube that uses an electron beam to create images on a fluorescent screen. It was commonly used in televisions and computer monitors before the advent of flat-screen technology.

2. How does an electron travel in a CRT?

Electrons are generated at the cathode, a negatively charged electrode, and accelerated towards the anode, a positively charged electrode, by an electric field. The electrons then travel in a straight line until they hit the fluorescent screen, creating an image.

3. What factors affect the trajectory of an electron in a CRT?

The trajectory of an electron in a CRT is affected by its initial velocity, the strength of the electric and magnetic fields, and any external forces acting on the electron. These factors can be controlled to manipulate the electron's path and create different images on the screen.

4. How is the trajectory of an electron in a CRT used in televisions and monitors?

The trajectory of an electron in a CRT is used to create images on the screen by controlling the intensity and direction of the electron beam. The electron beam is directed towards specific areas of the screen, causing phosphors on the screen to light up and create the desired image.

5. What are the potential hazards of working with CRTs?

CRTs contain a high voltage power supply and generate X-rays, which can be harmful to human health. It is important to handle CRTs carefully and follow safety precautions when working with them to avoid potential hazards.

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