Electrical Engineering ⇒ Topic : Power Rating of a Resistor

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Power Rating of a Resistor The ability of a resistor to dissipate power as heat without destructive temperature buildup is called power rating of the resistor. Power rating of resistor = I^{2}R or r V^{2}/R [See Fig. (A)]
FIGURE (A) Suppose the power rating of a resistor is 2 W. It means that I^{2}R or V^{2}/R should not exceed 2 W. Suppose the quantity I^{2}R (or V^{2}/R) for this resistor becomes 4 W. The resistor is able to dissipate 2 W as heat and the remaining 2 W will start building up the temperature. In a matter of seconds, the resistor will burn out.The physical size of a resistor is not necessarily related to its resistance value but rather to its power rating. A large resistor is able to dissipate (throw off) more heat because of its large physical size. In general, the greater the physical size of a resistor, the greater is its power rating and viceversa.  
 
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