The focal length, like you said it's the distance between the FOCAL point and the mirror.
Hope this helps.... :)
Volume will decrease over time, the more particles removed, is making the volume decrease.
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If a cell is placed in an isotonic solution, there will be no net flow of water into or out of the cell, and the cell's volume will remain stable. If the solute concentration outside the cell is the same as inside the cell, and the solutes cannot cross the membrane, then that solution is isotonic to the cell.
Condensation releases water
