Quick Electric Charge question (1 Viewer)

[Shoom]

hi
7.3 x 10^19 electrons passed through a certain point in 4 mins. Calculate the charge.

If a positive coulomb of 1 charge (or something) was placed next to a positive coulomb of 2 charges (or something)
(it was +1 and +2 though)
Draw the electric field around them and the null point

 

[Js^-1]

Um, I think you have to go to the definition of current. Its a certain amount of electrons passing a point per second. I don't remember exactly. As for the second question...hmm...beats me. Does the 2+ one just have more field lines? Or closer spaced?

 

[VenomP]

hi
7.3 x 10^19 electrons passed through a certain point in 4 mins. Calculate the charge.

If a positive coulomb of 1 charge (or something) was placed next to a positive coulomb of 2 charges (or something)
(it was +1 and +2 though)
Draw the electric field around them and the null point

For the second question...

The two charges repel, so there will be field lines going AWAY from the two charges and nothing inbetween them (since diagrams show the flow of negative particles in a field).

The null point will be in the middle of the two points, but since one is 2x as strong as the other, the null point will be twice as far from the stronger charge as the other charge. (i.e. the distances of the charges will be 1/3cm and 2/3cm from the null point)

I couldn't find an image on the net, and i can't draw, so hopefully that description is enough.


As for the first question...I'm working on it...Can't remember the formula.

 

[Js^-1]

Got this from wikipedia.
For an electric current of 1 ampere, 1 coulomb of electric charge (which consists of about 6.242 × 10^18 electrons) drifts every second through any imaginary plane through which the conductor passes.

Should be easy enough to work it out with that information.

 

[3unitz]

hi
7.3 x 10^19 electrons passed through a certain point in 4 mins. Calculate the charge.

If a positive coulomb of 1 charge (or something) was placed next to a positive coulomb of 2 charges (or something)
(it was +1 and +2 though)
Draw the electric field around them and the null point

1)
charge on 1 electron = -1.6 x 10^-19 C

charge = charge per electron x number of electrons
Q = (-1.6 x 10^-19) x (7.3 x 10^19)
Q = -11.68 C

the 4min is not needed for the calculation, but would be used if the question further asked for the current (I = Q/t)

2)
electric field diagram: View attachment 17108

- although not drawn on the diagram, twice as many electric field lines should leave the 2C charge as the 1C charge.

- arrows indicate the direction that a positive charge would move if placed in that field. since like charges repel, they move outwards

- null point is where magnitude of E is 0 (i.e. a charge placed at the null point will experience a net force of 0 due to the charges).

to find the distance of the point from the charges recall that the magnitude of the electric field is given by the equation: E = kQ/r^2.
we want the magnitude of the electric field from the 1C charge E₁ = k1/r₁²to be equal to the magnitude of the electric field from the 2C charge E₂ = k2/r₂²

k1/r₁²= k2/r₂²
r₂² = 2r₁²
r₂ = sqrt 2 r₁

i.e. r₂ is approximately 1.41 times the distance of r₁

not double:

The null point will be in the middle of the two points, but since one is 2x as strong as the other, the null point will be twice as far from the stronger charge as the other charge. (i.e. the distances of the charges will be 1/3cm and 2/3cm from the null point)

 

[Js^-1]

Wow, that was very useful. Thanks man.

*Runs off to study*