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What is Physics Good For?

Warming up on... RC circuits

This assignment is due before 9 AM, Monday, September 24^th, 2007.

Please type your last name and first initial (e.g., Rader, A):

Please type a nickname: (in case your answer gets used in class).

The following questions refer to the material you were to read in preparation to the lesson. Please write a three or four sentence response to each of the questions.

You may change your mind as often as you wish. When you are satisfied with your responses, click the SUBMIT HOMEWORK button at the bottom of this page.

WarmUp questions are worth 4 points.

1.

In the circuit to the right, the voltage across the resistor depends on the current that passes through it (Ohm's law), and the voltage across the capacitor depends on the charge on it (Q=CV). Is there a relationship between the curent through the resistor and the charge on the capacitor? How about the current through the battery?

2.

A 1 mF capacitor is charged up to 1000 V and then allowed to discharge through a 100 k resistor. Estimate how long it takes before the voltage across the capacitor has dropped to a safe value. Note: this is why you should NOT poke around inside a TV set if you do not know what you are doing.

3.

Consider a circuit like the one shown. A long time after the switch is thrown, the capacitor will have an (approximately) constant charge (Q) and voltage (V). If the value of the resistor is increased, which of the following statements is true?

Q will be less, but V will be unaffected.

V will be less, but Q will be unaffected.

Q and V will both be less.

Neither Q nor V will be affected at all.

V will be less but Q will be greater.

Q will be less but V will be greater.

Both Q and V will be greater.

Below is a space for your thoughts, including general comments about today's assignment. What was hard or confusing (or cool)? What would you like to spend extra time on in class? Do you see how this subject fits in with the others we have discussed?

You may change your mind as often as you wish. When you are satisfied with your responses click the SUBMIT button.

This site is made possible by funding from the National Science Foundation (DUE-9981111).

This assignment is due before 9 AM, Monday, September 24th, 2007.

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This assignment is due before 9 AM, Monday, September 24^th, 2007.