AC current and incandescent bulbs

In summary, during the experiment, the frequencies of both the incandescent bulb and the CFL bulb were found to be 120hz, which is twice the frequency of the 60hz wall plug. This is because the AC current flows through the filament twice in each period, causing it to "power up" twice and resulting in the flicker frequency of 120hz. The large "DC offset" in the incandescent bulb is due to the filament taking time to completely turn off, and this can be calculated by looking at the time between each peak of AC current.
  • #1
KozakDave
2
0
In my class we did an experiment where we measured the flicker frequency of an incandescent bulb and a CFL bulb (powered by a 60hz wall plug) using a photodiode and a oscilloscope. We were then asked some questions about the sinusoidal curves that were produced.



1. The incandescent bulb probably has a large "DC offset". Why do you think this is?
(im struggling with this question. Does it have something to do with the filament heating up?)



2. Is the flicker frequency for each of them the same as the 60hz wall plug frequency? why or why not?

From the experiment I found out that the frequencies were 120hz but I don't know why?



Please help
 
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  • #2
KozakDave said:
1. The incandescent bulb probably has a large "DC offset". Why do you think this is?
(im struggling with this question. Does it have something to do with the filament heating up?)
You're definitely on the right track. If you're in a room that's only illuminated by an incandescent bulb, you can tell that it takes a noticeable amount of time for it to completely turn off.

Try calculating how much time passes between each peak of AC that flows through the filament of the bulb.

KozakDave said:
2. Is the flicker frequency for each of them the same as the 60hz wall plug frequency? why or why not?

From the experiment I found out that the frequencies were 120hz but I don't know why?
Have a look at its sinusoidal current waveform. How many peaks are there in a period?
 
  • #3
1. So maybe because the energy doesn't totally dissipate before the next peak of AC current? The wave is just a big higher because its starting at a different point?

2. So there is two peaks in each period. One in the positive and the other in the negative y axis. So are you trying to say that each peak equates to 60 hz? so why isn't the ac current considered 120hz?
 
  • #4
KozakDave said:
1. So maybe because the energy doesn't totally dissipate before the next peak of AC current? The wave is just a big higher because its starting at a different point?
I think you have the right idea. Try to formulate it in terms of filament temperature instead.

KozakDave said:
2. So there is two peaks in each period. One in the positive and the other in the negative y axis. So are you trying to say that each peak equates to 60 hz?
No, but since you have two peaks in each period of AC, the bulb "powers up" twice in a period (it doesn't care about current direction). That means something for the frequency of the power waveform and, as a consequence, the frequency of the flickering.
 
  • #5


1. Yes, the DC offset in the incandescent bulb is due to the filament heating up. As the filament heats up, it becomes a better conductor and reduces the resistance of the circuit, allowing more current to flow. This results in a DC offset in the sinusoidal curve as the current is not constant but fluctuating due to the heating and cooling of the filament.

2. No, the flicker frequency for each of them is not the same as the 60hz wall plug frequency. The 60hz frequency is the frequency of the AC current that is supplied to the bulb. However, the flicker frequency of the bulb is determined by the rate at which the filament heats up and cools down, which is influenced by the resistance and capacitance of the bulb. In the case of the incandescent bulb, the filament takes longer to heat up and cool down compared to the CFL bulb, resulting in a flicker frequency of 120hz. This is because the incandescent bulb has a higher resistance and lower capacitance compared to the CFL bulb.
 

What is the difference between AC and DC current?

AC (alternating current) is a type of electrical current that periodically changes direction, while DC (direct current) flows in one direction. AC is commonly used in household and industrial settings, while DC is commonly used in batteries and electronic devices.

How does an incandescent bulb work?

An incandescent bulb works by passing an electrical current through a thin filament, causing it to heat up and emit light. The filament is typically made of tungsten, which has a high melting point and can withstand the high temperatures required for light production.

Why are incandescent bulbs being phased out?

Incandescent bulbs are being phased out due to their low energy efficiency. They waste a lot of energy as heat, and only about 10% of the energy they use is converted into light. This makes them more expensive to operate and contributes to environmental concerns.

Can AC current be used to power an incandescent bulb?

Yes, AC current is commonly used to power incandescent bulbs. The alternating current allows the filament to heat up and produce light continuously.

What are the advantages and disadvantages of using incandescent bulbs?

Some advantages of incandescent bulbs include their low cost and ability to produce warm, natural-looking light. However, they have a short lifespan, are not energy-efficient, and can be a fire hazard if not handled properly.

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