A lightbulb, where electrical energy is transformed into light energy (usefull) and heat (wasted)
A hydroelectric generator, where one kinetic energy (moving water) is transformed into another kinetic energy (spinning turbines), which in turn is transformed into electrical energy (useful), sound energy (waste) and heat (waste)
A battery in an electrical circuit where chemical potential energy is transformed into electrical energy
A solar cell where light energy is transformed into electrical energy.
