Class Exercise Feb 2

__Question__: A charge q_{1} = 1m
C is at the origin. A second charge q_{2} is at x = 3 m on
the x-axis. Find the electric field at point P with coordinates
*x*
= 0 , *y* = 1 m.

__Solution__

We need to find the electric field produced by each charge and add them.

The field

The distance r_{2} from the 4 microC charge to P is sqrt(10)
m (10 =1^{2} + 3^{2 }by Pythagoras' theorem) and
the the second electric field contribution is:

E_{x} = -E_{2} cos (angle between E vector and x-axis)

= - k(4 microC)/(10 m^{2})(3/sqrt(10))

= - (9x10^{9}_{ } N.m^{2}/C^{2})(4
microC)(3)/(10sqrt(10) m^{2})

= - 3.4x10^{3} N/C

= k(1 microC)/(1 m

=(9x10

=1.0x10