The image in the left panel can be thought of as a -[br][br]- [b][color=#0000ff]BLUE[/color][/b] circle surrounded by a [b][color=#38761D]GREEN[/color][/b] annulus, [br][br]or the equator of a -[br][br]- [b][color=#0000ff]BLUE[/color][/b] sphere surrounded by a [b][color=#38761D]GREEN[/color][/b] spherical shell.[br][br]You can vary the thickness of the [annulus,shell] by dragging the yellow dot.[br][br]How do the curves in the right panel vary with the ratio of the radii?[br][br][color=#ff0000][i][b]What questions could/would you put to your students base on this applet?[/b][/i][/color]