Because resistors dissipate heat energy as the electric currents through them overcome
the ”friction” of their resistance, resistors are also rated in terms of how much heat energy
they can dissipate without overheating and sustaining damage. Naturally, this power rating is
specified in the physical unit of ”watts.” Most resistors found in small electronic devices such as
portable radios are rated at 1/4 (0.25) watt or less. The power rating of any resistor is roughly
proportional to its physical size. Note in the first resistor photograph how the power ratings
relate with size: the bigger the resistor, the higher its power dissipation rating. Also note how
resistances (in ohms) have nothing to do with size!