CRT direction of field in accelerating zone

[acherentia]

My textbook says that since the electrons are accelerated to the right in a CRT the field direction is to the left. This leaves me confused, because according to this model the field lines are pointing out from the electrons instead of pointing into the electrons. I thought that field lines are supposed to point into negative charge? Anyone can tell me where I go wrong?

 

[rcgldr]

The front of a CRT is essentially a positively charged plate, while the electron source is essentially a negatively charged point source, so the field direction is from front to back, which is to the left in the case you mentioned.

 

[acherentia]

I keep forgetting that a charge cannot feel its own field, so obviously the field is not the electrons' field but a field that the electrons are subject to. Thank you.

 

[acherentia]

How does the electric field produce acceleration in the moving electrons?

F=ma=qE?

My textbook gives a value for E CRT of 8.0 X 10^5 N/C. Which if this was a constant number, according to my calculations a=1.41 x 10^17 m/s^2.

But I also know that E=kQ/r^2. Since r is changing as the electrons are moving closer and closer into the field, so r is getting smaller and smaller, shouldn't the value of E be constantly changing.

If the value of E is constantly changing as electrons move closer to it, how did they come up with the number 8.0 X 10^5 N/C for E?

 

[PJC01]

The direction of the electric field in an accelerating zone of a CRT (cathode ray tube) is determined by the direction of motion of the electrons. In this case, the electrons are accelerated to the right, which means that the electric field must be pointing in the opposite direction, to the left. This is because the electric field is what accelerates the electrons, and the direction of the force on a charged particle is always perpendicular to the direction of its motion.

It is important to note that the direction of the electric field is not determined by the charge of the particle, but rather by the direction of the force on that particle. In this case, the electrons are negatively charged, but they are being accelerated to the right, so the electric field must be pointing to the left.

It is also important to understand that field lines do not necessarily point into negative charge. Field lines represent the direction and strength of the electric field, not the direction of charge. In fact, field lines always point away from positive charges and towards negative charges, but this does not mean that they cannot also point in other directions depending on the situation.

In summary, the direction of the electric field in an accelerating zone of a CRT is determined by the direction of motion of the electrons, not the charge of the particles. The field lines represent the direction and strength of the electric field, not the direction of charge. It is important to understand these concepts in order to properly interpret and analyze the behavior of charged particles in electric fields.