What is the first law of conservation of energy? how is the law applicable to the earths energy balance

First law of thermodynamic state that energy is always conserved, in other word, energy cannot be created or destroyed.

This means that energy can only transfer from one source to another.

For example, the electricity we used to power our phone didn't come from nowhere.

We charge our phone using the energy from the electricity from the outlet.

The outlet gets its energy from the power plant, who generated that energy from burning coal.

The coal they burned got their energy while they were alive as plants.

The plants got their energy from the sun.

The sun got its energy from other cosmic stuff and so on...

My point is that the energy we use will always cycle around. It doesn't come from thin air and it doesn't disappear into thin air either. This help keeps things balance because if energy is created out of thin air then the earth might just blow up. If energy gets erased into thin air then there'll be nothing to fuel life.

photocells convert light energy to electricity

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.