Class Exercise Jan 30

__Question__: A charge Q = 6m C is at
point P_{1} with coordinates *x* = 2 m , *y* = 1 m. Find
the electric field at point P_{2} with coordinates *x* = 1
m , *y* = 2 m. Find the force on a charge q = -2m
C placed at point P_{2.}

__Solution__

1. Draw a clear diagram showing points P_{1} and P_{2}
.

2. Draw the vector

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 *r*^{2}. Don't forget to include the
units.

*r*^{2} = (1m)^{2} + (1m)^{2} = 2 m^{2}

5. Use Coulomb's law to calculate the electric field at point P_{2}.
Remember that electric field is a __vector__. Draw the vector on your
diagram with its tail at point P_{2}.

6. Calculate the force on the charge q.