Does the lightbulb burn? (Faraday)

In summary, the professor said that if you close the switch, the upper lightbulb (n° 2) will go out. You can argue that it does or does not happen, depending on the wire resistance of the combination.
  • #1
nonequilibrium
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Apologies for the atrocious attempt at a drawing:

attachment.php?attachmentid=26567&stc=1&d=1277039056.gif


So my professor said that if you close the switch, the upper lightbulb (n° 2) will go out. How exactly do you know this? Well of course, if you replace the changing magnetic field that is inducing an emf with a battery somewhere close to lightbulb 1, it is evident the 2nd bulb will go out once you close the switch, and that you can argue with 1/R = 1/R_a + 1/R_b. But this doesn't seem to be a valid argument in this case, does it? Because I could say "imagine the (B-field replacing) battery is not close to the first bulb, but rather close to 2, on that little piece between the bulb and the rectangular connection, in which case the other bulb would stop burning if you closed the switch."

I suppose I would've found it most logical if all the bulbs kept burning once you closed the switch, but apparently this is not the case. How would one argue light bulb 2 goes out?

Thank you,
mr. vodka

EDIT: Is maybe the following reasoning a correct way to do this: (R_1: first bulb; R_2: second)
Close the switch. Go around the circular loop: I_1 R_1 + I_2 R_2 = emf
Go around the loop containing the switch and bulb 1: I_1 R_1 = emf
=> I_2 = 0
 

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  • #2
hi mr. vodka! :smile:

(try using the X2 icon just above the Reply box :wink:)
mr. vodka said:
Close the switch. Go around the circular loop: I_1 R_1 + I_2 R_2 = emf
Go around the loop containing the switch and bulb 1: I_1 R_1 = emf
=> I_2 = 0

Even quicker : go round the top loop (switch and top bulb) …

there's no emf in it, and no magnetic flux through it, so I2R2 = 0. :wink:
 
  • #3
The bulb is a resistance. When the switch is closed, current prefers taking the zero-resistance path than go through the bulb.

In a parallel resistance combination, lesser current flows through the larger resistance.
I1 = R2/(R1 + R2) & I2 = R1/(R1 + R2)
This is a limiting case. AS the wire resistance is zero, current flowing through the bulb is zero.
 

What is Faraday's law of induction?

Faraday's law of induction states that a changing magnetic field will induce an electric current in a conductor.

How does this relate to a lightbulb burning out?

When an electric current flows through a lightbulb, it produces heat and light. This current is supplied by the flow of electrons through a conductor, such as a wire. According to Faraday's law, a changing magnetic field can induce an electric current in a conductor. When the lightbulb is turned on, the changing magnetic field in the circuit can cause an electric current to flow through the filament, which eventually leads to the filament burning out.

Why do lightbulbs burn out in the first place?

Lightbulbs burn out due to the gradual deterioration of the filament, which is the thin wire inside the bulb that produces light when heated by an electric current. Over time, the filament will weaken and eventually break, causing the lightbulb to stop working.

Can Faraday's law be applied to other electrical devices?

Yes, Faraday's law can be applied to a variety of electrical devices, including motors, generators, and transformers. These devices all involve the use of changing magnetic fields to induce electric currents.

Is there any way to prevent a lightbulb from burning out?

Unfortunately, there is no way to prevent a lightbulb from eventually burning out. However, using higher quality bulbs and avoiding frequent on and off cycles can help prolong the lifespan of a lightbulb.

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