Home

WarmUp

What is Physics Good For?

Warming up on... Electric Charges, Forces and Fields

This assignment is due before 9 AM, Monday, August 27^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 assignments are worth 4 points each.

1.

In your book, equation 21.7 gives an expression for the electric field of a point charge. This expression contains "r hat", which is described as "a unit vector that points along the line from source point to field point." In your own words, please explain why "r hat" is a useful piece of notation. Be careful, you may need to explain what makes any notation useful.

2.

Let's say you are holding two tennis balls (one in each hand) and let's say these balls each have a charge Q, so they repel each other. If Q is too big, you won't be able to hold on to them. Estimate the maximum Q you can handle.
Hint: click the word "estimate" to get a little more info about what is expected here.

3.

A whole ring has a net charge of Q, spread evenly over its surface. Explain what you would need to know to determine the charge on a piece of the ring with angle theta.

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, August 27th, 2007.

1.

2.

3.

This assignment is due before 9 AM, Monday, August 27^th, 2007.