Why the power of concave lence is negative

For concave lens the power is negative because the focal length is negative. ... For a converging lens the focal length is taken as positive and for a diverging lens the focal length is taken as negative. As the concave lens is a diverging lens the focal length is negative. Hence power is negative.

Magma  is composed of molten rock and is  stored  in the earth's crust. lava is  magma  that reaches the surface of our planet through a volcano vent.

What does the start look like