Coulomb's law gives the electric force between two point charges. The force gets larger when the charges are larger and gets smaller with the square.
Like gravity between masses, but for charges. Double the distance and the force drops to one quarter. Double either charge and the force doubles.
Showing a random 20 of 50 problems.
Example 1
medium
A charge +q at x=0 and +4q at x=L. Find where on the segment the net force on a test charge is zero.
Example 2
challenge
A charge +Q sits at the origin and +9Q at x=L. A third charge q is placed somewhere between so it experiences zero net force. Find x.
Example 3
hard
Two charges +3μC and +12μC are 0.6 m apart. Where on the segment between them is the electric field zero?+3μC at 0, +12μC at 0.6 m — electric field zero at x
Example 4
hard
Three charges in a line: +q at x=0, −2q at x=L, and a test +q at x=2L. Find the net force on the test charge in terms of kq2/L2.+q at 0, −2q at L, test +q at 2L; net force
Example 5
easy
If both charges in a pair are negative, the force is ___.
Example 6
easy
Two +1μC charges are 0.1 m apart. Find the force. Use k=9×109 N·m²/C².
Example 7
easy
Charges q1=5 C, q2=2 C, separation r=10 m. Find the force. Use k=9×109.
Example 8
easy
Two charges q1=2 C, q2=3 C are r=3 m apart. Find the force. Use k=9×109.
Example 9
medium
Two charges repel with 8 N at 2 m. What is the force at 1 m?Find the new repulsive force when r goes from 2 m to 1 m (original F
Example 10
medium
Two charges q1=3×10−6 C and q2=5×10−6 C are separated by 0.2 m. What is the electrostatic force between them? Use k=9×109 N m2/C2.Electrostatic force on q₁ (q₁=3μC, q₂=5μC, r=0.2 m)
Example 11
medium
Two protons are 10−10 m apart. Find the magnitude of the Coulomb force. Use k=9×109 and e=1.6×10−19 C.
Example 12
challenge
A charge +q at x=0 and +4q at x=L. Where on the segment is the net force on a test charge zero?
Example 13
easy
What is the value and units of Coulomb's constant k?
Example 14
hard
Two identical pith balls (each 5 g) hang from 0.5 m silk threads and repel until they are 0.04 m apart, hanging at θ from vertical. Estimate the charge on each. Use g=10 m/s2, k=9×109.FBD of 5 g pith ball; balls 0.04 m apart on 0.5 m threads — find charge q
Example 15
easy
The electric force between two point charges varies as the inverse ___ of the distance.
Example 16
easy
Two 1 C charges are 1 m apart. Find the force. Use k=9×109.
Example 17
medium
Two charges feel 20 N. If both charges double, find the new force.
Example 18
easy
Two charges q1=2μC and q2=3μC are separated by 0.3 m. Find the magnitude of the force. Use k=9×109 N·m²/C².Force on q₁
Example 19
medium
Two equal charges q are 3 m apart and repel with 10 N. Find q. Use k=9×109.
Example 20
medium
Coulomb's law applies to point charges or to ___ charge distributions.