What is the equivalent resistance of two 20 W resistors in series?

The equivalent resistance of resistors in series is calculated by simply adding their resistances together. In this case, each resistor has a resistance of 20 ohms. Therefore, when two resistors of 20 ohms are connected in series, the total resistance is calculated as:

Total resistance = Resistance of first resistor + Resistance of second resistor = 20 ohms + 20 ohms = 40 ohms.

This direct addition illustrates the foundational principle of series circuits, where the total resistance increases with the addition of each resistor. Thus, the correct answer of 40 ohms accurately reflects this calculation.