# The SE of a particle in a ring

## Homework Statement

Write down the Schrödinger equation for a particle inside a circle of radius R

## The Attempt at a Solution

Take the gradient in spherical form and set r = R; θ=90;∅ as 0

Then you are left with the first two terms of the gradient where sin(90) = 1 and r = R.

I thought I was approaching this correctly but the solutions show this

(d/dr)^2 + 1/r (d/dr) + 1/r^2 (d/dθ)^2

I am not sure how are why you should get three three when the way I am thinking of it "phi" term will be zero.

Thanks for any help in advance!

Anand