Q. In my lab parts, the 1-watt resistors are bigger than the 1/2-watt ones, and the 2-watt resistor is the biggest of them all. Why are higher-power resistors bigger?
A. A resistor converts electrical energy into heat. The rate at which heat is produced is determined by the power the resistor must handle. The greater the power, the more heat is developed. The resistor has to get rid of the heat or it will get hotter and hotter until it burns up. To do this, the resistor must have a greater surface area, because the heat is transferred from the surface of the resistor to the air around it. Also, the heat energy must be spread throughout the mass of the resistor. The greater the mass, the less concentrated the heat energy is.