Power Dissipated on light bulb

In summary, the resistor dissipates power when connected to a 100W light bulb. The current is .8333 times the resistance of the bulb, and the power dissipated is 99.99 Watts.
  • #1
eatsleep
42
0
1. A 25 ohm resistor is connected in series with a 100 W light bulb. The standard 120V/60Hz AC outlet voltage is applied to the series combination. Determine the real power dissipated on the light bulb. Assume the internal resistance of the light bulb is independent of the power dissipation. Round off your answer to two decimal places.



2. P=Vrms x Irms



3. I used 120 V as Vrms. To find Irms I did 120/25. Is power lost over the resistor? Thanks in advance
 
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  • #2
What is the resistance of the light bulb? Then, what is the current? And finally, what is the power dissipated by the light bulb?
 
  • #3
estsleep - A 100W light bulb only dissipates 100W when connected directly to 120VAC.
 
  • #4
eatsleep said:
1. A 25 ohm resistor is connected in series with a 100 W light bulb. The standard 120V/60Hz AC outlet voltage is applied to the series combination. Determine the real power dissipated on the light bulb. Assume the internal resistance of the light bulb is independent of the power dissipation. Round off your answer to two decimal places.



2. P=Vrms x Irms



3. I used 120 V as Vrms. To find Irms I did 120/25. Is power lost over the resistor? Thanks in advance

120/25 would be the current in the resistor if the resistor were connected directly across the 120V. But it's not - there is a light bulb in series with it dropping some of the voltage ...
 
  • #5
can i use the formula P = V^2/R to find the resistance of the bulb? so, 100 = 120^2/R. R=1440 ohms?
 
  • #6
eatsleep said:
can i use the formula P = V^2/R to find the resistance of the bulb? so, 100 = 120^2/R. R=1440 ohms?

Almost. I compute 144 ohms.
 
  • #7
ok, to find the current can I just Vrms/R? 120/144 = .8333. Then power is I^2 x R. Doing that gives me 99.99
 
  • #8
No, because the 120V is not all across the light bulb, is it?
 
  • #9
Will doing voltage division to find the Vrms over the bulb work? Then finding the Irms from Vrms/Rbulb?
 
  • #10
eatsleep said:
Will doing voltage division to find the Vrms over the bulb work? Then finding the Irms from Vrms/Rbulb?

Yes it would.
 
  • #11
rude man said:
Yes it would.

got it! thanks for the help
 

Related to Power Dissipated on light bulb

1. What is power dissipation?

Power dissipation refers to the amount of energy that is lost or converted into heat when an electrical device, such as a light bulb, is in operation. It is typically measured in Watts (W).

2. How is power dissipation calculated?

Power dissipation can be calculated by multiplying the voltage across a device by the current flowing through it. This can be expressed as P = VI, where P is power, V is voltage, and I is current.

3. How does power dissipation affect a light bulb?

The power dissipated by a light bulb directly affects its brightness and lifespan. The more power that is dissipated, the brighter the light bulb will be, but also the faster it will burn out.

4. What factors can affect the power dissipation of a light bulb?

The power dissipation of a light bulb can be affected by the type of bulb, its wattage, the voltage of the power source, and the environment in which it is used. For example, a higher wattage bulb will have a higher power dissipation than a lower wattage bulb.

5. How can power dissipation be reduced in a light bulb?

To reduce the power dissipation of a light bulb, you can use a lower wattage bulb, decrease the voltage supplied to the bulb, or use more energy-efficient bulbs, such as LED or CFL bulbs, which have lower power dissipation compared to traditional incandescent bulbs.

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