I believe all the insulators would be glass, wood, plastic, and yarn.
But I’m not entirely sure if mechanical pencil lead is an insulator or conductor.
Hope this helps.
I think it is 100 dB .I holp it is help.
The focal length would likely decrease as the refractive index and the increase when the curvature radius of the lens increases. The decrease in focal length happens since a higher index of refraction would signify that the rays of the sun striking to an object would tend to bend more.