Varying the voltage of a light bulb

[sanado]

Hey guys, was wondering if you could help me with this question:

What determines the brightness of a lightbulb?

I think it would be power (and therefor voltage and current since P = VI) as power is used in the measurement of energy delivered. Why is it the case then that, from the questions i am doing, it states that if you have a simple circuit such as the one shown in the following link (page 11, question 5), why doesn't the brightness vary when one part of the parrallel circuit is removed?

http://www.vcaa.vic.edu.au/vce/studies/physics/pastexams/physics12004.pdf

Question 5, page 11

Thanks

 

[Mapes]

I don't see the contradiction. There's no power associated with the removed bulb, so it's dark. The power is unchanged for the others*, so their brightness is unchanged.

*P = VI = V²/R, and voltage and resistance are constant.

 

[baba89]

for your question! The brightness of a light bulb is indeed determined by the power it receives, which is a combination of voltage and current. When the voltage of a light bulb is varied, it affects the amount of current flowing through the bulb, thus changing the power and ultimately the brightness. However, in the circuit described in question 5 on page 11, the voltage is kept constant while the resistance is varied by removing a part of the parallel circuit. This means that the current flowing through the circuit remains relatively constant, resulting in a consistent power and brightness for the light bulb.

In order to see a change in brightness, the voltage must be varied, as this directly affects the amount of current flowing through the circuit. Removing a part of the parallel circuit does not significantly change the voltage or current, thus the brightness remains constant.

It is important to note that the brightness of a light bulb can also be affected by other factors such as the type of bulb, the materials used, and the temperature. These may also need to be taken into consideration when conducting experiments or analyzing data. I hope this helps clarify the concept for you!