Peoples Physics Concepts

http://www.ck12.org Chapter 14. Magnetism

For instance, if a positively charged particle is moving to the right, and it enters a magnetic field pointing towards

the top of your page, it feels a force going out of the page, while if a positively charged particle is moving to the

left, and it enters a magnetic field pointing towards the top of your page, it feels a force going into the page:

Example 1: Find the Magnetic Field

Question: An electron is moving to the east at a speed of 1. 8 × 106 m/s. It feels a force in the upward direction

with a magnitude of 2. 2 × 10 −^12 N. What is the magnitude and direction of the magnetic field this electron just

passed through?

Answer: There are two parts to this question, the magnitude of the electric field and the direction. We will first

focus on the magnitude.

To find the magnitude we will use the equation

FB=qvBsinθ

We were given the force of the magnetic field( 2. 2 × 10 −^12 N)and the velocity that the electron is traveling

( 1. 8 × 106 m/s). We also know the charge of the electron( 1. 6 × 10 −^19 C). Also, because the electron’s velocity is

perpendicular to the field, we do not have to deal with sinθbecause sinθof 90 degrees is 1. Therefore all we have

to do is solve for B and plug in the known values to get the answer.

FB=qvBsinθ

Solving for B:

B=

FB

qvsinθ