# Electr. and Magnetism

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1) A charge of 80nC is uniformly distributed along the x-axis from x= 0 to x= 2.0m. Determine the magnitude of the electric field at a point on the x-axis with x=8.0m.

a] 30 N/C
b] 15 N/C
c] 48 N/C
d] 90 N/C
e] 60 N/C

2) 3 point charges, 2 positive and one negative, each having a magnitude of 20uC are placed at the vertices of an equilateral triangle (30 cm on a side). What is the magnitude of the electrostatic force on one of the positive charges?

a]69N
b]40N
c]80N
d]57N
e]20N

• Electr. and Magnetism -

1. (b) is closest. You need to use Coulomb's law and integrate the effect of charge from x = 0 to 2, and include the factor epsilono

2. When you use Coulomb's Law to add the vector electrostatic forces, the resultant will be parallel to the opposite side of the triangle.

F = 2 *20uC* epsilon0*sin 30/(0.3)^2
= (20 uC)^2*epsilono /0.09 m^2
= 40 N

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