Uniform Electric Field

Question

I was going through the first chapter in Resnick Halliday related to electromagnetism and then I came across something called a uniform electric field. It was written that "If E is uniform (that is, constant in magnitude and direction),then the acceleration of the particle is constant" So my question is: 1)How can E be constant in magnitude? E depends on F and since F follows an inverse square law therefore the magnitude of E should decrease as we move away? 2)Does E have a direction? I was taught that since pressure in a fluid extends in all directions therefore pressure is a scalar quantity. Therefore I can give a similar reasoning to an electric field since it extends in all directions. Also how can it be constant in direction as per the statement given in the book?

I think I am flawed in my fundamentals. N.B: I am relatively new to these topics and electric field is the first thing they have in books. So please try to explain in simple words.

Essentially a duplicate of http://physics.stackexchange.com/q/172768/2451 — Qmechanic, Apr 01 '15 at 19:56

score 1 · Accepted Answer · answered Apr 01 '15 at 19:50

1

How can E be constant in magnitude? E depends on F and since F follows an inverse square law therefore the magnitude of E should decrease as we move away?

The 1/r² inverse square law only applies for a pointlike source. If you contrive a number of pointlike sources into a column (see the infinite line on Andrew Duffy's physics course), the force diminishes in a 1/r fashion. Then if you contrive them into a sheet, the force doesn't diminish at all. See the infinite wall on mathspages. That's about gravity, but the same principle applies.

Does E have a direction?

No. It's usually depicted with a direction, as per this picture, which is again from Andrew Duffy's course.

enter image description here

But the arrowheads are an oversimplification. Two electrons repel, two positrons repel, and an electron and a positron attract. At some future date you'll come to appreciate that an electron or a positron has an electromagnetic field, wherein the positron has the opposite chirality to the electron.

answered Apr 01 '15 at 19:50

John Duffield

11,097

So does something like a uniform electric field exist in nature or is it just something we use to simplify our calculations in physics(like an ideal situation)? Also if something like that does exist then wouldn't it violate Coulumb's law? – Karan Singh Apr 02 '15 at 10:43
I'm not sure about nature, but all we're talking about is charged plates. It doesn't violate Coulomb's law. – John Duffield Apr 02 '15 at 16:48
How can you restrict the electrostatic force and not violate coulumbs law? – Karan Singh Apr 02 '15 at 16:50
Because Coulomb's law applies to charged particles with a spherical symmetry. That's why the 4π is in the expression F=q1q2/4πε0r². – John Duffield Apr 02 '15 at 17:10

Uniform Electric Field

1 Answers1

Linked

Related