It does not really work that way. Think of a power line as a garden hose pressurized with water. Every time a pinhole is made water will flow out of the hose, but the hose remains pressurized. This is very simplistic, but I hope it helps with your understanding. Brownouts occur when too many pinholes are made, and the pressure (voltage) in the power grid drops. The pressure is voltage, the flow is amperage. So electricity is never 'unused' it just stays as electric potential in the grid.

The quick answer is that there is no 'unused current'. When you switch a light bulb you connect it to a power source - effectively the powerstation that is converting the prime power source - energy in coal or nuclea fision - which gets converted to electricity. The power station is committed to generate electrical power at a standard frequency and voltage. As more people switch on light bulbs and all manner of other elctrically powered applicances, the demand on the power station increases which in almost all powerstations means that the steam throttle is opened to provide more enegy to the turbines that drive the electrical generators. All this happens automatically and smoothly. Listen to the engine of a small gasoline powered stand-by generator. When you start it up it hums along at a constant speed. Connect a load such as a power tool or flood light and you will hear the engine load up to maintain the same speed. If you look close at the carburettor as the load is switched on you will see the throttle open allowing more gas into the engine so it can generate more power. Turn off the power tool and the generator returns to humming mode - generating no electricity - so there never is any 'unused current'

Without current flow, no electrical power is consumed. If the water pressure in the hose is akin to voltage, the volume of water that leaves the hose is akin to current. So unused current is just that - unused. It's like the water left in the hose when you close the valve.

according this question,electric current flows only when it is in use, so there is no unused current at all.

It just sits there. It's supply and demand. It gets used when it's needed.

If never enters the system. Think of generators as pumps, if they are trying to push more current than is being used they run the risk of being damaged which is why the grid is so closely monitored. This is also what leads to cascading failures of the grid. If there is a single disconnect it can case "backpressure" on these generators and burn them out so failsafe switches quickly disconnect the generators from the grid which can lead to the next system seeing the excess capacity and disconnecting, and so on...

The electric power grid is an example of something called a "servomechanism" where there is feedback that keeps the fuel intake of the generators (and therefore the amount of power they put out) closely related to demand for power. In the morning when millions of people get up, flip on lights, put on the coffee and so forth, it sucks electricity out of the system. Automatic equipment therefore pumps more fuel to the generators so that the amount of power going INTO the system remains fairly stable. It's not perfectly stable, of course, which is why really sensitive equipment like computers requires surge protectors and either an uninterruptable power supply or at least an automatic shutdown. Too bad most refrigerators don't have that also, since a brownout can burn out the compressor motor.

To expand on the other excellent answers. Consider Ohm's law: V=IR where: V=voltage I=current R=resistance The power station provides a constant voltage (120 V in North America). All the appliances and devices plugged into a socket make up the combined resistance (R). The current (I) that flows is dependant on the resistance. When more things are turned on, resistance DECREASES. This is because each house and appliance is connected in parallel. The combined resistance 2 devices in parallel is 1/(1/R+1/R). For 3 devices, it is 1/(1/R+1/R+1/R). As more devices are added, the denominator gets larger and larger, so the combined resistance gets smaller and smaller. From the equation, V=IR, if R goes down and V stays at a constant 120V, then I must go up. Similary, if people turn things off, then R goes up, so current must go down.

The energy in the electricity can be lost. And it transmits into energy outside the cable. The electricity in an ordinary house normally has protection around its enery, and the the electrons stay together without it going somewhere else. But, if the cable has no protection it may lose some energy. That energy might not be noticed but it is lost. To try it out you may do an experiment. Get two cables: one without anything around the cable and another with. connect them with a batery or into an outlet (CAREFUL!) and see it for your self. If you get an ordinary power measurer. You can find that a small amount of energy is lost. Where does that energy go? well, it goes to the air, and combines with other atoms and matter/material...

Current never remains unused.Its always flows provided the circuit is closed.when the grid is not in operation it remains at a higher potential .when the grig circuit is closed or load is despatched load current stats flowing to lower potential areas.Current is never stagnant. no current in open circuit only flows in case of close criciut.

There actually is always some unused electricity in the system - reactive power (measured in Volt-Amps Reactive (VAR). All alternating-current systems have this issue. All lines, transformers, motors, and other devices have properties of capacitance and inductance, both of which store or delay current or voltage for a brief period. The result is that you have voltages and currents that are out of phase with each other. The amount of phase difference is expressed as "power factor." Though these out-of-phase components don't do any useful work, they circulate through the system and can affect system voltage, among other things. To counteract the negative effects of reactive power, utilities (and, often, large customers) use banks of capacitors and inductors at strategic locations. They can either be switched by system operators or electronic devices (one automatic device is called a Static VAR Compensator.) Controlling generator excitation and using special synchronous motors called "condensers" are other ways that VARs can be kept under control.