Can the Brightness of Bulbs in a Parallel Circuit be Equal?

In summary, the conversation discusses 1 (e) on a physics exam, where the solution states that all on-bulbs in 1 (e) glow with equal brightness. The questioner is confused about how this is possible due to different currents in different branches. The response clarifies that the equivalent resistance is R/2, and the current through each bulb is V/R. The conversation then touches on the concept of infinite light and energy with parallel light bulbs, with the clarification that it is an infinite amount of current at a finite voltage.
  • #1
ehrenfest
2,020
1
Can someone help me with 1 (e) at the following site:

http://ocw.mit.edu/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/29B6C858-A92B-431F-A43E-725D58A768EF/0/exam1.pdf

The solutions say that all on-bulbs in 1 (e) glow with equal brightness. But how is that possible because in e-c, the equivalence resistance is

(2/R) so the total current is V * R/2 and the current through each branch is V * R. In e-b, the current is V/R through B, which is different, right?
 
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  • #2
ehrenfest said:
Can someone help me with 1 (e) at the following site:

http://ocw.mit.edu/NR/rdonlyres/Physics/8-02Electricity-and-MagnetismSpring2002/29B6C858-A92B-431F-A43E-725D58A768EF/0/exam1.pdf

The solutions say that all on-bulbs in 1 (e) glow with equal brightness. But how is that possible because in e-c, the equivalence resistance is

(2/R) so the total current is V * R/2 and the current through each branch is V * R. In e-b, the current is V/R through B, which is different, right?

2/R as the equivalent resistance is wrong. It should be R/2. You don't need to find the equivalent resistance though. The current through a resistor is just the voltage across the resistor divided by resistance. For e-c, the voltage across bulb B is V... the resistance of bulb B is R, so the current through bulb B is V/R... exactly the same way, the current through bulb C is V/R.
 
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  • #3
I see. But you can just keep adding more and more light bulbs in parallel and they will each glow as bright as a single light bulb? Doesn't that allow you to generate an infinite amount of light (energy) with a finite amount of voltage?

Yes, we are assuming the wires have negligable resistance. But this still seems fishy to me...
 
  • #4
They are in parallel so it's an infinite amount of light with an infinite amount of current. This isn't a problem as an infinite amount of current at a finitie voltage gives an infinitie amount of energy - of course paying the bill might be tricky!
 

1. Why is my circuit not lighting up?

The most common reason for a circuit not lighting up is a faulty or disconnected power source. Make sure that your power source is connected properly and that it is supplying enough voltage for your circuit to function.

2. How do I troubleshoot a circuit that is not lighting up?

Start by checking all of your connections to make sure they are secure. Then, use a multimeter to test the voltage at different points in your circuit. If you are not getting a voltage reading, there may be a problem with your power source or wiring. You can also try replacing any components that may be faulty.

3. Can using the wrong type of battery affect the brightness of my circuit?

Yes, using the wrong type of battery can definitely affect the brightness of your circuit. Different batteries have different voltage and current ratings, so using a battery with too low of a voltage or current output can result in a dim or non-functioning circuit.

4. How can I increase the brightness of my circuit?

There are a few ways to increase the brightness of your circuit. One way is to use a power source with a higher voltage output. You can also try replacing any resistors in your circuit with ones that have a lower resistance value, which will allow more current to flow through and increase the brightness. Additionally, using brighter LEDs or adding more LEDs in parallel can also increase the overall brightness.

5. What can cause a circuit to suddenly become dimmer?

One possible cause for a sudden decrease in circuit brightness is a decrease in power supply voltage. This can happen if the battery is dying or if there is a loose connection in the circuit. Another potential cause could be a faulty component, such as a resistor or LED, that is no longer functioning properly. It is important to check all connections and components to determine the root cause of the issue.

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