How Many 1W Bulbs Can I Use with 10.2W Power Source?

[Ezio3.1415]

Suppose I have 10.2 W power source... Now how many 1 W bulb can I use here?

Obviously I can use 10 bulbs at their best here... But can I use an eleventh one? Usually we do it like this 10.2/1=10.2~10 but my ques is there is some power left here... So why can't we use one more?

This will result in that bulb glowing dim? I am thinking maybe all of the 11 bulb will then glow dimmer... Maybe that's why we always take the floor of the number we get...

Am I right?

 

[berkeman]

Suppose I have 10.2 W power source... Now how many 1 W bulb can I use here?

Obviously I can use 10 bulbs at their best here... But can I use an eleventh one? Usually we do it like this 10.2/1=10.2~10 but my ques is there is some power left here... So why can't we use one more?

This will result in that bulb glowing dim? I am thinking maybe all of the 11 bulb will then glow dimmer... Maybe that's why we always take the floor of the number we get...

Am I right?

You are correct -- adding the last bulb will pull down the voltage of the power source, which will dim all of the other bulbs a little bit.

 

[Ezio3.1415]

Thank you...

 

[CWatters]

Hold on a moment. It's not really that simple. Berkeman gave you the short answer.

The 11th bulb might cause the output voltage to fall but not always. You can't really answer the question without knowing why the designer of the power supply specified a 10W limit.

It could be he specified a 10W limit so that the power supply wouldn't overheat when used in a hot climate. If you are in a nice air conditioned office the power supply might well deliver the full voltage at 11, 12, 13W or more without any problem.

On the other hand it might only appear to be happy delivering >10W at the full voltage. In reality some components inside might be operating slightly hotter then intended. That might reduce the life time of the product. The effect can be quite dramatic. The life expectancy of some capacitors can halve for every 10C rise in temperature over 20C. He might have limited it to 10W to ensure the company had an acceptable failure rate within the warranty period.

It could be berkeman is right and that the designer limited it to 10W to ensure the output voltage stayed within the design tolerance. However that doesn't mean the power supply voltage definitely will drop when slightly overloaded.

 

[Nickie]

Your thinking is correct. When it comes to electrical circuits, it is important to consider the power supply and the power consumption of the devices connected to it. In this case, you have a 10.2W power source and you want to connect 1W bulbs to it. As you correctly calculated, you can connect a maximum of 10 bulbs to this power source without overloading it.

If you try to add an 11th bulb, the power supply will still provide 10.2W of power, but now it will have to distribute this power among 11 bulbs instead of 10. This means that each bulb will receive less power and will therefore glow dimmer. In some cases, this may not be an issue, but in others, it could potentially damage the bulbs or the power source.

In general, it is always best to follow the floor rule when calculating the maximum number of devices that can be connected to a power source. This ensures that the power supply is not overloaded and that the devices connected to it receive the appropriate amount of power.