Energy conversion I have a simple and a dumb question.
If I have, say, a hydro-electric generator which is generating electricity, and I am not using this power for anything, is this hydro-electric power converted to something at this point? Where does this energy go?
 A: This is not a simple nor dumb question at all. 
The answer is complex, and really depends on the exact details of the control system for the power station in question. Essentially, there will be control systems in place, either active or passive, that are designed to try and make sure energy is not wasted in the way you may imagine. 
One way is to actively reduce the flow rate from the reservoir when power demand is low (via a valve, say). For short term demand fluctuations that would manifest themselves in changes in generator torque directly at the hydro-turbine, the turbine wheel would speed up, storing the excess energy as kinetic energy. This change in turbine rpm would result in a mismatch between the fluid speed at the turbine inlet and the turbine speed, which leads to reduced turbine efficiency. The wasted energy typically appears in the form of increased kinetic energy of the fluid at the turbine outlet.
However, generator systems in such power stations are typically designed to operate as much as possible at constant rpm. Various control systems are in place to ensure this is the case. The details are complex, and more a matter of engineering than of physics.
A: It goes into friction of your "Water wheel". And since you don't have a closed circuit, that energy is if we're looking at a steady state not being used. If you put some load in the circuit and closed the circuit, that would generate current inside the wire which would then do work. but the ammount of work it did would be pushing back on your "water wheel". The voltage and with it the current produced would have a value according to the force of water hitting your Wheel.
