What is proof by Converse?

Why does air only blow out of one side of a fan? What device converts electric energy into mechanical energy? What is the unit of rebar 14mm? How many pounds is 84g? Why are the bottoms of shoes called souls? Red green and blue light rays each enter a drop of water from the same direction Which light ray's path through the drop will benf the most and which will bend the last Why? How are the three types of heat transfer alike? How does a electrostatic generator work? What is a complete path for transfer of electricity? Active solar energy systems use long or short wave radiation? What travels at the light of speed? What are the dimensions of a 13 seer coil? In which type of waves is the motion of the particles perpendicular to the direction of the wave is traveling? What shows the movement of energy from one organism to another? As the frequency of a wave goes up what happens to the wavelength? Is down quark heavier than up quark because neutron is heavier than proton? If force moving an object points at least partially in the opposite direction if the objects motion the work is considered to be? How do you analyze a lamp? What will an object do if its density is greater than that of water? What happens to the temperatures of a hot and cold substance when they come into contact with each other?

What is proof by Converse?