How will a capacitor influence a lightbulb?

In summary, when the switch is closed in the given circuit, the light bulb will gradually get brighter as the capacitor charges and then gradually get dimmer as the capacitor discharges. The capacitor acts as a temporary "store" for the current, causing the light bulb to have a varying intensity.
  • #1
Dart82
57
0

Homework Statement


Consider the simple circuit shown below, in which a light bulb with resistance R and a capacitor with capacitance C are connected in series with a battery and an open switch. The capacitor has a large capacitance and is initially uncharged. The battery provides enough power to light the bulb when it is connected directly to the battery. What happens when the switch is closed?

[URL=http://imageshack.us][PLAIN]http://img169.imageshack.us/img169/229/question7lg1.gif[/URL][/PLAIN]


A) Nothing
B) The light bulb glows with a constant intensity.
C) The light bulb gradually gets brighter as time passes.
D) The light bulb starts out at its brightest and then gradually gets
dimmer as time passes. [my second guess]
E) The light bulb blinks on and off. [my 1st guess]

Homework Equations


no equation necessary



The Attempt at a Solution


My 1st thoughts:
Well i thought that the current would flow from the battery to the capacitor, where it would be stored. When the capacitor discharged it would send the current through the lightbulb, causing it to flash on and off.

Apparently this is faulty thinking, as E is not the correct answer.

my second thoughts: electrons flow from regions of low potential, such as those found on a - battery terminal to regions of higher potential. Therefore, the electrons will "flow" from the negative battery terminal across the closed switch and through the filament of the lightbulb, thus illuminating it. Next, the electrons will flow into the capacitor where they will be stored. As the capacitor's stored charge builds, it "sucks" more and more available current from the lightbulb, causing it to dim.

Feel free to poke any holes in my theory.
 

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  • #2
Youre second guess is correct. A capacitor will not discharge itself unless the battery is taken out of the circuit and a complete closed path remains. Take a look at figure 3 in this link: http://phoenix.phys.clemson.edu/labs/223/rc/index.html

As your capacitor charges, it will gain more voltage and the current in the circuit will decrease to zero
 
  • #3
Thanks for the help!
 
  • #4
When the switch is closed the current can flow in the circuit since the capacitor "absorbs" it. The bulb will therefore glow, but as the charge accumulates on the plates of the capacitor a voltage builds up over it. This voltage opposes that of the battery. The current in the circuit will then decrease as the voltage builds up over the capacitor and eventually stop when the capacitor is charged up to the same voltage as the battery. A charged capacitor acts like a battery, but its voltage drops as it discharges.
 

1. How does a capacitor affect the brightness of a lightbulb?

A capacitor can affect the brightness of a lightbulb by storing and releasing electrical energy. When connected in series with a lightbulb, the capacitor will charge and discharge at the same frequency as the alternating current (AC) powering the lightbulb. This can cause fluctuations in the current and voltage, resulting in a dimming or flickering effect on the lightbulb.

2. Can a capacitor make a lightbulb brighter?

Yes, a capacitor can make a lightbulb brighter by acting as a power factor correction device. This means that the capacitor can improve the efficiency of the circuit and provide a more stable current and voltage to the lightbulb, resulting in a brighter and more consistent light output.

3. How do the capacitance and voltage of a capacitor affect a lightbulb?

The capacitance and voltage of a capacitor can affect a lightbulb by determining the amount of electrical energy that can be stored and released. A higher capacitance and voltage can result in a larger amount of energy being supplied to the lightbulb, which can cause it to burn out or become damaged if it exceeds the recommended limits.

4. Can a capacitor be used to control the brightness of a lightbulb?

Yes, a capacitor can be used to control the brightness of a lightbulb by changing the amount of energy that is supplied to the lightbulb. By using a variable capacitor, the amount of electrical energy can be adjusted, which can result in a dimming or brightening effect on the lightbulb.

5. How does the type of capacitor used affect a lightbulb?

The type of capacitor used can affect a lightbulb by determining its capacitance, voltage rating, and temperature range. Different types of capacitors have different properties and can affect the circuit in different ways. For example, a ceramic capacitor may have a smaller capacitance but a higher voltage rating, while an electrolytic capacitor may have a larger capacitance but a lower voltage rating. The type of capacitor used should be chosen carefully to ensure proper functioning and compatibility with the lightbulb.

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