Water pipe: If more water pumps are used, what will happen to the flow of water?

Electric circuit: Two 9 V cells were used instead of a single 9 V cell, what will happen to the current of the circuit?

Electric circuit: Two 9 V cells were used instead of a single 9 V cell, what will happen to the brightness of the bulb.

Water pipe: If more water wheels are used, what will happen to the flow of water?

Electric circuit: A second light bulb was added to the circuit, what will happen to the current of the circuit?

Electric circuit: A second light bulb was added to the circuit, what will happen to the brightness of the bulb?

Bonus: What will happen to the brightness of the bulb when a resistor was added to the circuit? (Can you explain why?)