Physics QUestions!?

Question

1. From It's definition, the unit of electric field E is the N/C. An equivalent of E is v/m... why?

2. Why do ten million electrons placed on a solid copper sphere become uniformly distributed on the sphere's surface?

3. The force on an electron in an electric field of 200 v/m is 3.2x10 -17(
4. An electric field of magnitude 200 v/m can be produced by applying a potential difference of 10v to a pair of parallel metal plates by... (the answer is 5cm, but i dont know why..)

5. The resistance of a conductor does not depend on its mass, why?

6. A certain wire has resistance R. The resistance of another wire, identical with the first except for having twice its diameter is..

7. A certain peice of copper is to be shaped into a conductor of minimum resistance. Its length and cross section area should be: (answer is 1/2 L ans 2A) but why?

Answer 1

1.The field intensity (E) on a point charge (q) is the force on that ch age per that charge.
E=F/q
Work or energy is defined as force times distance or force required to move a particular change in the field E

W=Fd
F= W/d
E=F/q=W/(d q)
but W=Joule and Volt=Joule per Coulomb=J/q
E=(W/q)/d=V/d or V/m

2. Electrons are of the same sign so they do not like to play with each other. Imagine them all to be connected by compressed springs. At the point of equilibrium they will all be equally or optimally spaced along the surface of the sphere. If you pump some of the electros on to that sphere more they may escape in a form of a lightening.

3. Remember E=F/q
F=E q
Electron has a charge q=1.602 E-19 C
So
F=200 x 1.602 E-19= 3.204 E-17 N

4. E=V/d remember?
so d=V/E=10/200=.05m or 5cm

5. Resistance depends on the number of free electrons and is irrelevant to the mass which in turn depends on molecular bonding and mass of the nucleus.

6. I’ll supply a hint

R=p l/A
R resistance
p – resistivity of material
l - length of conductor
A – area of the conductor
And
A=pi r^2

7. Similarly to #6
Get back to me if you need more help

Answer 2

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