Magnitude of force on electron in magnetic field

[jaydnul]

Homework Statement

An electron in a vacuum is first accelerated by a voltage of 41300 V and then enters a region in which there is a uniform magnetic field of .145 T at right angles to the direction of the electron's motion.

What is the magnitude of the force on the electron due to the magnetic field?

Homework Equations

[itex]F=qvBsinθ[/itex]

The Attempt at a Solution

At first I though the 41300 V was just a number to throw me off (they do that a lot), but now I think it is important. I know the charge, magnetic field, and sin90=1. So the only thing I'm missing is velocity, but I have no clue how to calculate that from the information I was given. Any help?

Thanks

 

[Legaldose]

You can find the energy of an electron by using qV = U, where U is the Kinetic Energy of the particle. Then it's just a matter of solving for v from the KE equation.

EDIT: I should point out that the energy will be in eV, which you can then just use a conversion factor to get it into joules.

 

[rude man]

The electron is moving fast enough to warrant relativistic correction for calculating the velocity.

 

[jaydnul]

Perfect. Thanks

 

[Nickie]

for your question. It is important to consider all the information given in a problem, as it could all be relevant to finding the solution. In this case, the initial voltage of 41300 V is important because it tells us that the electron has been accelerated and has a specific kinetic energy. This kinetic energy can be used to calculate the velocity of the electron using the equation KE = 1/2mv^2, where KE is the kinetic energy, m is the mass of the electron, and v is the velocity.

Once you have calculated the velocity, you can use the equation F=qvBsinθ to find the magnitude of the force on the electron due to the magnetic field. Remember to use the charge of an electron, -1.602 x 10^-19 C, for q and the given values for B and θ.

I hope this helps. Keep in mind that in scientific problems, all information given is important and can be used to find the solution. It is also important to double check your units and make sure they are consistent throughout your calculations.