The dihedral works by increasing the lift on the low side. A wing tilted from level has less lift that one that is level. The greater the angle, the less lift. With dihedral, both wings are at an angle to level. As the plane rolls to one side, the high wing looses more lift, and the low wing gains lift as it goes to level. The high wing starts dropping and the low wing comes up. This is how the self righting is accomplished. When the plane is level, both wings are tipped an equal amount so there is equaliburium.(sp?). Of course, this assumes equal wing pannel sizes, balanced tip to tip, no warps and ailerons balanced. All of these can overide the dhideral effect.

Don