Activity 22.5.1. Warm-up Activity.
Is the magnitude of the net force on object A greater than, less than, or equal to that on object B? Explain your reasoning.
Section 22.5 Electric Superposition
Subsubsection Activities
Activity 22.5.2. Moving a Box.
Three students are trying to move a box that is preventing them from going home after a long day of doing physics. All the students are equally strong: that is, they can all exert a force of the same magnitude if they push on something. Each student has a different idea about how best to push on the box to get it to move. Which student do you most agree with?
Student A: “I think we should all spread out and push from different angles.”
Student B: “I think we should all try to push in the same direction.”
Student C: “I don’t think it matters: as long as three of us are pushing, our collective force will be the same.”
Activity 22.5.3. Non-uniform Wire.
A charge wire has one end at \(x = 0\) and the other end at \(x = L\text{.}\) You measure the charge density to be the following:
\begin{equation*}
\lambda(x) = \frac{q_o}{L^2}x
\end{equation*}
(a)
Sketch a charge diagram of the wire showing the charge density, using \(+\) and \(-\) symbols to represent positive and negative charge, respectively.
(b)
Determine the total charge on the wire.
Activity 22.5.4. Point Charges.
Two positive point charges are separated by a distance \(L\text{,}\) as shown in the figure.
(a)
Indicate the direction of the electric force exerted on each charge.
(b)
Compare the magnitudes of the forces.
(c)
The large point charge is split into two smaller point charges and separated, as shown in the figure, so that each new charge is still a distance \(L\) away from the upper charge.
Write a short sentence about how the magnitude of the net electric force on the upper charge has changed.
(d)
Suppose that when the large point charge is split into two smaller point charges, they are instead moved horizontally, so that each new charge lies along a horizontal line passing through the original point charge, as shown in the figure.
Write a short sentence about how the magnitude of the net electric force on the upper charge compares to both of the previous situations.
(e)
Suppose instead that the large point charge is spread uniformly across a horizontal line, as shown in the figure.
Explain why the magnitude of the net electric force on the upper charge is not the same as it is in any of the previous situations. Discuss possible methods you might use to calculate the electric force on \(+q\text{.}\) (You do not have to calculate this force.)
