A light-dimmer switch with a potentiometer

In summary, the conversation discusses the use of a variable resistor in light-dimmer switches and how the total resistance is proportional to the slide position. The question asks for the power expended in a light bulb when the slide is at position x = 0.5, with the given information that the bulb has a resistance of 205Ω and runs at 120 V. The solution involves finding the voltage or current across the bulb to calculate the power dissipated by its resistance.
  • #1
Asylum
3
0

Homework Statement


Some light-dimmer switches use a variable resistor as shown in figure. The slide moves from position x = 0 to x = 1, and the resistance up to slide position x is proportional to x (the total resistance is Rpot = 100Ω at x = 1). What is the power expended in the light bulb if x = 0.5?

Homework Equations


Rseries = R1 + R2 + ...
Rparallel = 1 / (1 / R1 + 1 / R2 + ...)
P = V2 / R = I2R

The Attempt at a Solution


I tried first to obtain the total resistance, which is 50 + 1 / (1 / 50 + 1 / 205), and use this number to divide the voltage squared in order to get the power, but this is not correct. I don't know what I'm missing here. Any help will be appreciated.
 

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  • #2
Hi Asylum, Welcome to Physics Forums.

Were you given any information about the bulb itself? It's resistance or power rating?
 
  • #3
gneill said:
Hi Asylum, Welcome to Physics Forums.

Were you given any information about the bulb itself? It's resistance or power rating?
Hello, I think the resistance for the bulb is 205Ω.
 
  • #4
Okay, that would make it a 70 Watt bulb running at 120 V.

What you're looking to find is the power dissipated by the bulb resistance alone. To that end you'll need to find either the voltage across it, the current through it, or both.
 
  • #5
gneill said:
Okay, that would make it a 70 Watt bulb running at 120 V.

What you're looking to find is the power dissipated by the bulb resistance alone. To that end you'll need to find either the voltage across it, the current through it, or both.
Thank you, I will try that now.
 

Related to A light-dimmer switch with a potentiometer

What is a light-dimmer switch with a potentiometer?

A light-dimmer switch with a potentiometer is a device that is used to control the brightness of a light source by adjusting the resistance of a potentiometer, which is a type of variable resistor. This allows for a gradual change in the amount of electricity flowing to the light, resulting in a dimming effect.

How does a light-dimmer switch with a potentiometer work?

A light-dimmer switch with a potentiometer works by adjusting the resistance of the potentiometer, which is connected in series with the light source. As the resistance increases, the amount of electricity flowing to the light decreases, causing it to dim. Similarly, when the resistance decreases, the light becomes brighter.

What are the advantages of using a light-dimmer switch with a potentiometer?

One of the main advantages of using a light-dimmer switch with a potentiometer is the ability to control the brightness of a light source. This can be useful for creating different moods and ambiances, as well as saving energy by using less electricity. Additionally, potentiometers are relatively inexpensive and easy to install, making them a convenient option for dimming lights.

Are there any potential drawbacks to using a light-dimmer switch with a potentiometer?

One potential drawback of using a light-dimmer switch with a potentiometer is that it can cause flickering or buzzing noises in some light fixtures. This is usually due to compatibility issues between the switch and the light source. It is important to make sure that the switch is compatible with the type of light being used to avoid these issues.

Can a light-dimmer switch with a potentiometer be used with any type of light bulb?

While most light-dimmer switches with potentiometers are designed for use with incandescent bulbs, there are also switches available that are compatible with LED and CFL bulbs. It is important to check the specifications of the switch to ensure that it is suitable for the type of bulb you are using.

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