- How does a home appliance limit the amount of current that flows
through it? - Are there some resistors set up in series in order to cut
down the current flow before it actually reaches the device?
Assuming that there are $15 \;\text{A}$ under $240 \;\text{V}$ in each socket, most appliances would burn/get destroyed if there was no limitation to the current draw. But that would mean that huge amounts of energy were wasted in form of thermal energy and I assume that's not the case.
- How does the electric circuit in our home "know" how much power to
deliver to each socket?
Best Answer
Your home circuit does not "know" how much current to deliver to each socket or appliance. The circuit supplies a constant voltage, and it is then up to each appliance to limit the current that it draws. Some simple appliances, such as lights with old incandescent bulbs or electric toasters or irons, are basically just a resistor (possible a variable resistor). Other appliances may contain a motor; the design of the motor will limit the current that it draws and this current will depend on the load on the motor.
Electronic circuits are often designed to run at a voltage that is lower than mains voltage, so electronic devices will typically have a circuit using transistors that supplies a very precise voltage to the rest of the device. Or they may work by charging an internal battery, which them provides current to the rest of the device - this then allows the devices to still be used when not directly connected to the mains supply.
Your home circuit (or each of the circuits, if your home has several) places an upper limit on the total current that can be drawn from it by using fuses. Individual appliances may also have fuses in their plugs or built into the appliances themselves. Some extension leads have their own fuses. But these fuses are intended to break the circuit in case of an accidental current surge (typically caused by a short-circuit somewhere) - they do not limit current in normal use.