Lamps connected in series with different voltages

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In summary, the question asks which lamp will glow the brightest in a series circuit where each lamp has double the voltage drop of the one to its left. The answer depends on the efficiency of the lamps and how brightness is defined, but generally, increasing the energy input will result in a brighter output.
  • #1
alacey11
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Homework Statement



5 lamps are connected in series (one after the other in a circle) across the terminals of an energy source. Each lamp has a voltage drop across its terminals that is double the value of the one to the left of it. Which lamp will glow the brightest?

Homework Equations



V = I x R

The Attempt at a Solution



I know how to apply Ohm's law to components of a circuit, and to the whole circuit. I understand that the current through all lamps is the same, and that they have different resistances and voltage drops across them, and I can calculate all that fine. It's just the brightness - I do not understand what makes a lamp brighter or dimmer.. Is it the voltage drop across the lamp that determines it brightness? Or is it the current? Thanks for any assistance!
 
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  • #2
Welcome to PhysicsForums!

This question requires you to think about series circuits. Here's a hint: how much current flows through each of these lightbulbs?

Note that power dissipated across a two-terminal element (like a resistor or a lightbulb) is calculated as: [itex]P=IV[/itex], the current through the element multiplied by the voltage drop across the element.

EDIT: Ooops... You already did all that! Okay, assume that each of these lightbulbs has the same efficiency, i.e. they convert the same percentage of power (dissipated across them) into light. I'd state this assumption for good measure.
 
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  • #3
The question as you put it is one of those questions where any answer you give could be right, provided you give a reason why.

Like Matlabdude alluded to, you have to mention the efficiency. If two bulbs have the same efficiency, (brightness/power) then of course more power will mean more brightness.

But in addition to that, it depends on how you define brightness - you can add all sorts of stipulating factors like: how intense is the light in a certain direction (Is a laser bright if you are looking at it from the opposite end?); how intense is the light in a certain color range (is it bright if it has a lot of UV?).

According to wikipedia, ( http://en.wikipedia.org/wiki/Brightness ) brightness is "an attribute of visual perception", so you could even get away with claiming they are equally bright to a blind person, or that what you think is the brightest may seem the darkest to a person with a strange neurological problem.

But after all that, for the general assumptions that a reasonable person might make, the bulbs will be of the same efficiency and design, so if you increase the energy going in, you will naturally increase the energy coming out.
 
  • #4
Thanks for your help!
The question made sense once it was explained, was simpler than I thought, thanks.
 
  • #5


I would approach this problem by first examining the relationship between voltage, current, and resistance in a circuit. From Ohm's law, we know that the voltage drop across a component is directly proportional to the current flowing through it and inversely proportional to its resistance. Therefore, the lamp with the highest voltage drop will have the highest current flowing through it, and thus will likely glow the brightest.

However, there are other factors that can affect the brightness of a lamp, such as the type of bulb and its efficiency. In addition, if the voltage source is not constant (e.g. a battery that drains over time), the brightness of the lamps may change over time as well.

To accurately determine which lamp will glow the brightest, we would need to know the specific values of voltage, current, and resistance for each lamp in the circuit, as well as any other relevant factors. Without this information, it is difficult to make a definitive determination.
 

1. How do I calculate the total voltage in a series circuit with different voltage lamps?

In a series circuit, the total voltage is equal to the sum of the individual voltages of each lamp. For example, if you have three lamps with voltages of 5V, 10V, and 15V, the total voltage would be 30V (5V + 10V + 15V = 30V).

2. Can I connect lamps with different voltages in series?

Yes, you can connect lamps with different voltages in series. The voltage of each lamp will determine the brightness of the lamp, with higher voltage lamps being brighter than lower voltage lamps.

3. Why do lamps in series with different voltages have different brightness levels?

Lamps in a series circuit with different voltages will have different brightness levels because the voltage determines the amount of current that flows through the circuit. The higher the voltage, the more current flows through the lamp, resulting in a brighter light.

4. What happens if one lamp in a series circuit burns out?

If one lamp in a series circuit burns out, the other lamps will not receive any current and will also turn off. This is because a series circuit has only one path for the current to flow, and if that path is interrupted, the circuit will be broken.

5. How does the voltage affect the lifespan of a lamp in a series circuit?

The voltage in a series circuit affects the lifespan of a lamp by determining the amount of current that flows through the lamp. Higher voltage lamps will have a shorter lifespan as they are exposed to more current, which can cause them to burn out more quickly. Lower voltage lamps will have a longer lifespan as they are exposed to less current.

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