Is the voltage dropped across a resistor a waste of energy?
Yes and no. the energy is converted into heat and emitted as ir radiation. However, if you want heat, such as in a heater or toaster, then it’s not a waste
it’s the cost of doing business. you need resistors to control voltages and currents in different parts of the circuit. the heat losses in the resistances represent an entropy that must be generated when a useful thermodynamic work is done.
in a nutshell, yes. unless you wish to use the dissipated heat for a useful purpose. Electric heaters are usually simple resistors.
you can easily calculate the power dissipated by the resistor by multiplying the voltage drop by the square of the current flowing through the resistor.
in the sense that energy is thrown in the form of heat, yes. Thermal management is a problem, and the loss of power over resistors is an important part, especially in designs where real estate is a major concern. the challenge is to lose as little power as possible on the resistive components. it’s fun, during the first five minutes 🙂
The main function of the resistance is to limit the current.
For example, in a normal fan controller, the resistor was used to decrease the output current on the output side, or perhaps another reason was the use of the resistor bank.
The main application of the resistor is to limit the current and provide a stable output. Therefore, if it is considered a waste of energy, it may be inappropriate.
Of course, a voltage drop in a resistor is a loss of energy.
Again, it is a waste of energy if it is not used for heating purposes (for example, in an electric heater) provided the heat is sufficient.
this is not necessarily a loss! a resistor is usually found a circuit to regulate the voltage to a next piece. you can call it wasting energy, but you can also call hot air from an air conditioner condenser. you must use resistors as a necessary evil to operate the circuits. engineers like to minimize wasted energy.
jpl uses power resistors as heating elements to apply heat sensibly to items that require heat! Just select a resistor that will give the desired heat, screw it to where a little heat is needed, solder the controller power leads to the resistor, and inject a little bit of RTL on the exposed wiring and you have instant radiators. really impressed me!