Qualitative/quantitative translation (QQT)
Electric field inside and outside a thick charged slab
- Unit 8
- 8 points
- About 18 minutes
You can use a calculator on this question, just like on exam day.
A shorter multipart problem that connects reasoning in words with an equation. You make and justify a claim without equations, derive an equation from a physics principle, and then explain whether the two agree or use them to predict what happens in a changed situation. On the exam: Question 4 of 4. Section II has 4 questions in 95 minutes (50% of the exam score), one of each type in this order; calculator and equation sheet allowed. The CED suggests 15–20 minutes.
The question
A very large, flat slab of nonconducting material has thickness 2d and a uniform positive volume charge density ρ. Its faces are parallel to each other at x = −d and x = +d, so the slab's center plane is at x = 0. Consider only points far from the slab's edges.
Suggested time: 18 minutes
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Part (a)
3 points(i) Rank the magnitudes of the electric field at x = 0, x = d/2, and x = d. (ii) Is the magnitude of the electric field at x = 2d greater than, less than, or equal to the magnitude at x = 3d? Justify your answers. Do not use equations in this part; reason in words.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (b)
3 pointsDerive expressions for the magnitude of the electric field (i) inside the slab, at a distance x from the center plane (0 ≤ x ≤ d), and (ii) outside the slab (x ≥ d).
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (c)
2 pointsExplain how your expressions from part (b) agree with your reasoning in part (a).
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
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