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Learning Introductory Physics with Activities

Section 22.11 Application: The Charged Wire

Subsubsection Activities

Activity 22.11.1. The Charged Wire.

A total charge \(+q\) is spread uniformly over a wire of length \(L\text{.}\) You want to determine the electric field at the indicated point.
A horizontal wire of length L.  A point is labeled a distance y above the center.
Figure 22.11.1. A charged wire.

(a)

Predict: What direction do you expect the electric field to point? Do you expect its magnitude to be bigger, smaller or equal to \(\frac{kq}{y^2}\) ?

(b)

Chop the object up into pieces. Label at least one \(dq\) and identify relevant quantities. What is \(dq\) in terms of known quantities? What is \(r\text{?}\) What is \(\hat{r}\text{?}\)

(c)

Multiply the relevant quantities together to find \(\vec{dE}\text{.}\)

(d)

Add the \(\vec{dE}\) over the entire wire!

(e)

Make sense of your answer. Do the units check out? What happens as \(L \rightarrow 0\text{?}\) As \(y \rightarrow \inf\text{?}\) As \(y \rightarrow 0\)
Hint.
Remember to state: (a) Your expectation of what will happen, (b) a physical description why that should happen, and (c) a verification that your expression matches your expectation.