Question

For your initial post to the discussion, read through these steps before you begin, and then follow each step and answer the associated questions:

• Make a capacitor by filling a paper cup with water. The cup can be one that has been used previously, and doesn't need to be new. What is the analog of voltage in this case, and what is the capacitance?
• Poke a small hole on the side of the paper cup near the bottom and let the water drain out. How is this similar to an RC circuit?
• Now decrease the R by making the hole slightly larger in diameter and re-run the demonstration. How is the rate of water flow consistent with the new RC value?
• Time how long it takes the cup to drain in each case and estimate the drainage rate (ounces or milliliters per second), make note of it, and compare the two. Take a picture of the water flow in each case to illustrate the difference in flow rates. Include your observations in your post.

If you are unable to locate the items needed for the above experiment description, you can do a thought experiment. Think about the steps above and what observations you would make if you were able to complete it.

Answer 1

A capacitor stores electric charge, this generates a difference in electrical potential between the plates. In the case shown, the vessel stores a mass of water, which would be analogous to the electric charge. The potential difference would be the level difference between the upper and lower surface, the height would be analogous to the potential difference.

In the case of the hole, water will flow through it, this flow is analogous to the electric current. This is similar to the RC constant that indicates the time at which the capacitor is discharged to 0.632 of its initial value.

If the hole increases in size, this decreases the resistance, so we have a greater flow of water or current in the case of an electrical circuit, this because it increases the value of the RC constant.