Questions

In a spreadsheet program, when a data is changed all calculations are recalculated.

Multiple users can't share a local temporary table

In chemistry rusting is called as oxidation. Oxidation is a chemical process where metal gains oxygen and become oxide. In rusting the Iron ore make a chemical reaction with the oxygen in the presence of water and environmental or atmospheric moisture to produce an Iron oxide. Iron oxide is otherwise called as rust.

The rusting of iron is a chemical change because it is two substances reacting together to make a new substance. 

Rusting would only be a physical change if iron molecules remained pure iron throughout the process.

Alternating Current (AC) is the current in which flow of current is altered periodically whereas in DC current i.e, direct current the flow of current is only in one direction.

Some of the sources of AC current are :

1. Hydro-electric generators

2. Thermal power generators

3. Nuclear  power generators...

When the resistance of the air between breaks down the current flows from the positive cloud to the negative cloud in a flash which we call lightning . The difference of potential involves is very high.