Glass Objects in Cycles

Hello Everyone,

After doing some materials in cycles we thought now it should go fine.
A new problem came while doing glass material in cycles.
Amit has model Petri dish in Blender it was first render Blender Render engine.

Reference Image

Blender Render

But problem occur when he was doing material in cycles render engine.
The material looks like opaque glass.

Render Preview in Cycles

Render Preview in Cycles

The same problem had occurred earlier when I was doing Cycles material of Reagent bottle and cap.
That time I thought it was because of some error in  modeling and remodel the cap again and the problem solved.

Petri dish I checked the model again exported the models in other file deleted material than redone them again but the output was same.

But when I was learning Blender back 2009 that time I had one problem regarding face normal and how it can be solved by doing Ctrl + N key to realigned all the normals in one general direction.
And this did the trick.

After the correction

Final render after correction

The vertex normals and face normals decide how the direction of lights fall upon the face and how the surface material reacts to the light rays.
Its basic of the class 10th science. about ray refection and refraction when light rays hits a surface.