What is the actual power of a small light bulb marked 6V 3W connected to a 3V power supply?

What is the actual power of a small light bulb marked 6V 3W connected to a 3V power supply?

RL = (U) 2 / P = (6V) 2 / 3W = 12 Ω
Practual = U2 / r = (3V) 2 / 12 Ω = 0.75w
Hope to help you!

There is a small light bulb marked with 6V 10 Ω, which is connected to a 9V power supply. In order to make the light bulb shine normally, how much resistance needs to be connected in series?

I = u / r = 6V / 10 Ω = 0.6A
R=U/I=3V/0.6A=5Ω

A 1.5-volt, 1.5-Watt bulb with a name plate is connected to a 6-volt power supply to light normally. How large a resistor should be connected in series?

According to the name plate, the rated current of the bulb is I = 1a, and the resistance is r = 1.5 Ω
So when the current of the circuit is 1a, the bulb will light normally. From the voltage of 6V, the total resistance of the circuit is 6 Ω, so the resistance R = 6 Ω - 1.5 Ω = 4.5 Ω