# Charged Particle Motion in an Electric Field

" The hardest thing in the world to understand is the income tax"
Albert Einstein

• Having determined the electric field we now want to determine the behaviour of a point charge, q0, placed in this field.
• The force on the charge is given by  F = q0E.  But Newton's second law tells us that F = ma, so that the acceleration of the particle can be written, a = (q0/m)E.
• Once we have an expression for the acceleration it is usually possible to determine the trajectory of the particle, although in the general case this will involve solving differential equations.  However, when E is constant the acceleration is constant which allows us to use the kinematic equations describing motion under constant acceleration from the beginning of the first semester of this course (Physics 298).  Important equations in Physics should never be forgotten
• In two dimensions, with E constant in one direction and zero in the other, charged particle motion can be treated in the same way as projectile motion of a particle under the influence of a (constant) gravitational field.

What do you get if you have Avogadro's number of donkeys? Answer: molasses (a mole of asses)

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu