Electron Properties: Electric vs Magnetic Fields

[Mihai Dinu]

We can deflect a moving electron using an electric field or using a magnetic field. In order to obtain the same deviation, when the energy we should use is higher? Or, in other words, the "electric" or the "magnetic" property is stronger?

 

[DrClaude]

In order to obtain the same deviation, when the energy we should use is higher?

What about conservation of energy?

 

[Khashishi]

Take a look at https://en.wikipedia.org/wiki/Lorentz_force
For electrons moving less than the speed of light (always the case), the electric force is stronger. But for relativistic electrons, the forces are about equal.

 

[Vanadium 50]

the electric force is stronger

Only if B = E in those particular units.

 

[Mihai Dinu]

I try to choose the "cheapest energetic" way to deflect an electron, based on its known interactions. The electron has, also, a mass. Hypothetically, I could obtain same deflection as in previous case using this time gravitational attraction of another mass. How can this mass be compared with previous cases in terms of energy effort?

 

[DrClaude]

I try to choose the "cheapest energetic" way to deflect an electron, based on its known interactions.

Let me repeat myself: What about conservation of energy?

 

[Mihai Dinu]

Let me repeat myself: What about conservation of energy?

I understand. To obtain a certain same deviation, I have use the same energy, no matter what form it has.

 

[DrClaude]

I understand. To obtain a certain same deviation, I have use the same energy, no matter what form it has.

Yes

 

[sophiecentaur]

I need a bit of help with this. No work need be done on an object if its motion is circular. If we had a fixed pivot and a length of string, the Force X Distance would be zero. Where is the difference with circular motion in a magnetic field? Or are we discussion the Energy needed to set up the field?

 

[Khashishi]

Only if B = E in those particular units.

Yeah. That's the case in any reasonable system of units, in which electricity and magnetism are unified. Kind of hard to talk about an electromagnetic field, when the electric and magnetic fields have different dimensions.

 

[David Lewis]

As far as deflecting electrons, if you have high voltages handy, electric fields are usually a good option. But if it's easier to provide high currents then electromagnets might be a better choice. Neither type of force field is intrinsically stronger.

 

[Mihai Dinu]

As far as deflecting electrons, if you have high voltages handy, electric fields are usually a good option. But if it's easier to provide high currents then electromagnets might be a better choice. Neither type of force field is intrinsically stronger.

When the electron pass between the plates of a polarized (ideal) capacitor, the electric field modifies the trajectory of this electron. One billion electrons can follow and the capacitor field will be unchanged. Some work is done. Where comes this energy from?

 

[ZapperZ]

When the electron pass between the plates of a polarized (ideal) capacitor, the electric field modifies the trajectory of this electron. One billion electrons can follow and the capacitor field will be unchanged. Some work is done. Where comes this energy from?

Why isn't this obvious that it comes from the E-field? Turn off the field, no deflection.

Zz.

 

[Mihai Dinu]

Why isn't this obvious that it comes from the E-field? Turn off the field, no deflection.

Zz.

I can not turn off the field, because it comes from the electrons of one plate and the ions of the other plate, and their number is not changed, no matter how many free electrons cross this field.

 

[ZapperZ]

I can not turn off the field, because it comes from the electrons of one plate and the ions of the other plate, and their number is not changed, no matter how many free electrons cross this field.

You missed the entire point of my post!

Zz.

 

[Mihai Dinu]

You missed the entire point of my post!

Zz.

I tried to understand: Free electrons that cross the capacitor static field change trajectories, so work is done, but the capacitor field rest unchanged forever. Where comes the new energy from?
Now I think at this scenario: the incoming kinetic electron starts to interact with the capacitor field and transferes energy to capacitor field by disturbing one by one the electrons from the plates, upto the moment when the capacitor field starts to restore its minimum state and pushes out the disturbing electron. So the electron gets no new energy, only a new trajectory - if case.

 

[David Lewis]

Correct. No energy need be consumed in deflecting electrons. You could use a permanent magnet, for example. There may be an energy input required to maintain an electric field (replace charge leakage) or magnetic field (resistance of the coil).

 

[ZapperZ]

I tried to understand: Free electrons that cross the capacitor static field change trajectories, so work is done, but the capacitor field rest unchanged forever. Where comes the new energy from?
Now I think at this scenario: the incoming kinetic electron starts to interact with the capacitor field and transferes energy to capacitor field by disturbing one by one the electrons from the plates, upto the moment when the capacitor field starts to restore its minimum state and pushes out the disturbing electron. So the electron gets no new energy, only a new trajectory - if case.

This is incorrect for electrons in electric field, and certainly not true for uniform electric field such as that found in between parallel plate capacitors. The electrons gain kinetic energy from the E-field. This is similar to projectile motion in uniform gravitational field. So it isn't just a change in trajectory, as is the case for uniform magnetic field. There IS KE change! It is how we accelerate charged particles in particle accelerators.

Zz.