Final answer:
To find the power dissipated by bulb A when the switch is closed, we need to know the current flowing through or voltage across the bulb and its resistance to use the power formulas P = I2R or P = V2/R.
Step-by-step explanation:
The power dissipated by bulb A when the switch is closed can be calculated using the formula P = I2R, where P is power, I is current, and R is resistance. Assuming the setup involves a simple series or parallel circuit, we need the values of current through or voltage across the bulb and its resistance to calculate the power dissipated.
If we consider the reference case given where a voltage source is 120 V and a bulb is nominally rated at 75 W, we can use the power formula P = V2/R after calculating the resistance from the bulb's rating. For real applications, one might also account for wire resistance or the presence of other circuit elements, as this affects the total current in the circuit and therefore the power dissipated by each component.