Seniority of Wattage vs. Amperage

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Discussion Overview

The discussion revolves around the relationship between wattage, voltage, and amperage in light bulbs, particularly focusing on whether a constant wattage can be maintained while varying voltage. Participants explore implications for both simple and more complex circuitry.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions if a 100-watt bulb can function normally if the voltage is varied while keeping wattage constant.
  • Several participants assert that the bulb will draw current based on the voltage applied, leading to a discussion on the relationship defined by the power equation P = V x I.
  • There is a debate about whether varying voltage affects the wattage of a light bulb, with participants providing different interpretations of Ohm's Law.
  • One participant proposes a method to run a 120V bulb on a 240V line by adding resistance, which is met with strong objections regarding safety and practicality.
  • Concerns are raised about the dangers of working with high voltage circuits, emphasizing the need for understanding basic electrical concepts before experimentation.
  • Another participant requests clarification on the difference between series and parallel circuits, indicating a lack of understanding in this area.
  • Participants express concern for safety, particularly regarding the potential for electrical shock and fire hazards when working with AC mains circuits.

Areas of Agreement / Disagreement

Participants generally disagree on the feasibility and safety of running a 120V bulb on a 240V line, with some advocating for theoretical exploration while others emphasize safety concerns. The discussion remains unresolved regarding the practical application of the proposed methods.

Contextual Notes

There are limitations in the discussion regarding assumptions about circuit behavior, safety protocols, and the understanding of electrical concepts among participants. The mathematical steps and implications of the proposed methods are not fully resolved.

Who May Find This Useful

This discussion may be of interest to individuals exploring electrical engineering concepts, particularly those curious about the interplay between voltage, current, and power in circuits.

mearvk
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Was wondering if I kept the wattage for say a 100 watt bulb constant but varied the voltage would the light be able to continue functioning normally?

Also, assuming this is true does this hold for more complicated circuitry?

Thanks.
 
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You don't have that freedom. The bulb looks at the voltage and decides what current it will draw. The power is then VxI.
 
Antiphon said:
You don't have that freedom. The bulb looks at the voltage and decides what current it will draw. The power is then VxI.

The bulb sees 120 volts. We know it would draw about .83 amps, right? 120x.83 = 100

The bulb sees 240 volts. Would it then draw half as many amps?

The bulb sees 60 volts. Would it then draw twice as many amps?

More generally, does varying the voltage affect the wattage of a light bulb?
 
Last edited:
mearvk said:
The bulb sees 120 volts. We know it would draw about 8.3 amps, right? 120x8.3 = 100

The bulb sees 240 volts. Would it then draw half as many amps?

The bulb sees 60 volts. Would it then draw twice as many amps?

More generally, does varying the voltage affect the wattage of a light bulb?

Are you familiar with Ohm's Law? If you increase the voltage across a resistor, what does that do to the current through the resistor?

I = V/R

P = V^2/R = I^2 * R
 
Antiphon said:
You don't have that freedom. The bulb looks at the voltage and decides what current it will draw. The power is then VxI.

Never anthropomorphise lightbulbs. They hate it when you do that. :-p
 
So if I wanted to keep 100 watts going to a bulb with 144 ohms of resistance and I doubled the voltage to 240 I'd need to add 432 ohms (576-144) worth of resistance to the circuit?

So in theory I could run a 120v 100 watt light bulb on a 240v line if this were added: http://goo.gl/vy2Ig

Thanks for fielding my questions guys.
 
Last edited by a moderator:
So if I wanted to keep 100 watts going to a bulb with 144 ohms of resistance and I doubled the voltage to 240 I'd need to add 432 ohms (576-144) worth of resistance to the circuit?

So in theory I could run a 120v 100 watt light bulb on a 240v line if this were added: http://goo.gl/vy2Ig

Don't, Don't and Don't again.

Apart form the fact that what you propose will not work, This is a serious safety issue. 240 volt mains is seriously more dangerous than 120 volt mains.

If you must run a 120 volt bulb from 240 then run two in series. This will work safely.
Do not connect them in parallel, all you will achieve is two blown bulbs.

Do you understand what series means?
 
Last edited by a moderator:
Well is my math at least right?

If so, why would it be dangerous aside from the extra voltage?

Could you explain simply the diff between series and parallel?
 
Instead of trying to tell experts (and there are quite a few more expert than I am) here how to do something, how about just explaining your goal ie what you want to achieve and asking for help.
 
  • #10
mearvk said:
Well is my math at least right?

If so, why would it be dangerous aside from the extra voltage?

Could you explain simply the diff between series and parallel?

You don't understand the difference between series and parallel circuits, and you are wanting to start off working with AC Mains circuits? That's not a good thing to do. Please learn the basics of electricity and electronics first, and then find a good local mentor who can help you safely learn about working with AC Mains circuits. The shock and fire hazards are very real when working with those kinds of voltages and that much available power.

Here is your starter on series and parallel circuits:

http://en.wikipedia.org/wiki/Series_and_parallel_circuits

.
 
  • #11
Berkeman you seem to have a short circuit between 'theoretical' and 'actual'. I can ask questions all day about 240v circuits without being silly enough to try to power a 100w light bulb off of it.
 
  • #12
mearvk said:
Berkeman you seem to have a short circuit between 'theoretical' and 'actual'. I can ask questions all day about 240v circuits without being silly enough to try to power a 100w light bulb off of it.

Two problems...

First, you have not been clear that you do not intend to try any of this. We are genuinely concerned for your safety and those around you.

Second, when you post stuff like that in the forums, other newbies can see it and think that they can do it safely. Not a good idea.

We take safety seriously here at the PF. This thread is closed.
 

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