Physics 230 Spring 2002

Class Exercise Jan 30

Question: A charge Q = 6m C is at point P1 with coordinates x = 2 m , y = 1 m. Find the electric field at point P2 with coordinates x = 1 m , y = 2 m. Find the force on a charge q = -2m C placed at point P2.


1. Draw a clear diagram showing points P1 and P2 .

2. Draw the vector r on your diagram.

3. Find the components of the vector r.

From the triangle in the diagram, the x-component is - 1m and the y component is + 1m.

4. Find the value of r2. Don't forget to include the units.

r2 = (1m)2 + (1m)2 = 2 m2

5. Use Coulomb's law to calculate the electric field at point P2. Remember that electric field is a vector. Draw the vector on your diagram with its tail at point P2.

6. Calculate the force on the charge q.