Why Do Certain Answers Apply in Basic Electric Field Questions?

[DivideBy0]

Homework Statement

I'm confused about [question 16](http://image.prntscr.com/image/41a5c611927c44a7ac30104be3dd10ee.png) and [question 30](http://image.prntscr.com/image/a6aea3b9a8f04df9aca0dfe14054d4ce.png). The correct answers are e and a respectively.

Homework Equations

The Attempt at a Solution

For 16, why did D not work? Intuitively, I chose E because of parallel plates that have equal electric fields, but what is the integral for choice D and E and why are they different?

For 30, I thought higher voltage meant higher potential so I thought the answer should be C and D. Why is it A?

 

[kuruman]

Welcome to PF, DivideBy0.

16. The graph shows a uniform charge distribution, independent of x. Consider the charge distribution described in D. What does it look like? What do you know about the electric field that results from such a distribution?

30. You need to consider only one thing. The magnitude of the electric field can be approximated by $|\vec{E}|=|\frac{\Delta V}{\Delta s}|$. Where is this ratio the greatest?