What Electric Field is Needed to Undeflect Electrons in a Magnetic Field?

[Stryker321]

A beam of electrons is accelerated through a potential difference of 11kV before entering a velocity selector. If the B-field of the velocity selector is perpendicular to the velocity and has a value of 0.05 T, what value of the E-field is required (in the magnetic field region) if the particles are to be undeflected?

What I know:
F = qvB
and
F = qE

Therefore E = vB

But how on Earth do I find the velocity? Please help!

 

[nasu]

But how on Earth do I find the velocity? Please help!

Read this again:
"A beam of electrons is accelerated through a potential difference of 11kV"
What energy will the electrons have?

 

[baba89]

I understand your confusion about finding the velocity in this scenario. However, we can use the equations you mentioned to find the necessary E-field for the particles to be undeflected.

First, we can rearrange the equation F = qvB to solve for velocity, which gives us v = F/Bq. In this case, the force (F) is the product of the electron's charge (q) and the electric field (E). Plugging this into our equation, we get v = E/Bq.

Since we want the particles to be undeflected, we can set the force equal to zero. This means that the electric field must be equal to the magnetic field times the charge of the electron, or E = Bq.

Plugging in the given values of B = 0.05 T and q = -1.6 x 10^-19 C, we can calculate the necessary E-field to be 8 x 10^-21 V/m.

In summary, to have undeflected particles in the magnetic field region, the electric field must be equal to the product of the magnetic field and the charge of the particles. I hope this helps clarify the concept for you. Keep up the good work in your scientific studies!