Electromagnetism - Electric Potential

Question 3-4: refer to a thin, nonconducting ring of radius R, as shown below, which has a charge Q uniformly spread out on it.

  

The electric potential at a point P, which is located on the axis of symmetry a distance x from the center of the ring, is given by

A. Q / (4πɛ₀x)
B. Q / [4πɛ₀(R² + x²)^1/2]
C. Qx / [4πɛ₀(R² + x²)]
D. Qx / [4πɛ₀(R² + x²)^3/2]
E. QR / [4πɛ₀(R² + x²)]

(GR9677 #03)

Solution:

Electric Potential, V = kQ/r 
with k = 1/4πɛ₀

The distance r of P from the charged ring is r² = R² + x²

V = Q / [4πɛ₀(R² + x²)^1/2]

Answer: B