1. The problem statement, all variables and given/known data A semi-circle shaped cylindrical glass block has a radius of curvature of 10.0cm. and a refractive index of 1.50 as shown. A pin is placed at the centre of curvature O . How far from the surface do the pin appear to be when it is viewed along the axis of the spherical surface? 2. Relevant equations 3. The attempt at a solution The diagram is in the photo and the solution is in the photo , p/s : this is the notes from my senior. from the digram , I know that the object is placed on the left , whereas the refracting surface is concave relative to the the object . (assume the light pass from left to right). in the photo 2 , i was told that if refracting surface is concave relative to the the object , then the radius of curvature is negative... but here, the notes give the radius of curvature is positive. which on is correct? can someone help please?