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Suppose that, as a function of x, y, and z, an electric field has the following components:
Ex = 6x2y, Ey = 2x3 + 2y and Ez = 0
where E is measured in V/m and the distances are measured in m.

1) Find the electrical potential difference between the origin and the point x = -2.7 m, y = 4.1 m, z = 0.0 m.
2) Find the potential difference between the origin and the point x = 4.2 m, y = 5.9 m, z = 0.0 m.

Respuesta :

1) Potential difference: 144.6 V

2) Potential difference: -909 V

Explanation:

1)

Given an electric field in three dimensions, with components [tex]E_x,E_y,E_z[/tex], we have that each component of the field is related to the electric potential V by:

[tex]E_x=-\frac{dV}{dx}\\E_y=-\frac{dV}{dy}\\E_z=-\frac{dV}{dz}[/tex]

For the field in this problem, we know that

[tex]E_z=0[/tex]

Which means that

[tex]dE_z=-\frac{dV}{dz}\rightarrow dV=-dE_z dz=0[/tex]

and so the potential does not depend on z, so we can re-write it as [tex]V(x,y)[/tex].

Then we take the equation in x:

[tex]E_x=6x^2y=-\frac{dV}{dx}[/tex]

Solving for V,

[tex]V=-\int 6x^2 ydx =-6\frac{x^3}{3}y+f(y)=-2x^3y+f(y)[/tex]

where f(y) is a function depending on y.

From the equation in y,

[tex]E_y=-\frac{dV}{dy}[/tex]

And substituting the expression of V,

[tex]E_y=-\frac{d}{dy}(-2x^3y-f(y))=2x^3-f'(y)[/tex]

We know also that

[tex]E_y=2x^3+2y[/tex]

And by comparing these last 2 equations, we infer that

[tex]f'(y)=-2y\\f(y)=-\int 2ydy=-y^2+C[/tex]

So, the expression for the electric potential is

[tex]V(x,y)=-2x^3y-y^2+C[/tex]

where C is a constant.

Now we can find the electrical potential difference between the origin and the other point.

The origin has coordinates (0,0,0), so the potential is

[tex]V(0,0)=-2\cdot 0^3(0)-0^2+C=C[/tex] (V)

The other point has coordinates (-2.7 m,4.1 m,0.0 m), so the potential is

[tex]V(-2.7,4.1)=-2(-2.7)^3(4.1)-(4.1)^2+C=144.6+C[/tex] (V)

So, the potential difference is

[tex]\Delta V = 144.6 +C - C = 144.6 V[/tex]

2)

In this second case, we want to find the potential difference between the origin and another point.

The potential is

[tex]V(x,y)=-2x^3y-y^2+C[/tex]

The origin has coordinates (0,0,0), so the potential is

[tex]V(0,0)=-2\cdot 0^3(0)-0^2+C=C[/tex] (V)

The second point has coordinates (4.2 m, 5.9 m, 0.0 m), so the potential there is

[tex]V(4.2,5.9)=-2(4.2)^3(5.9)-(5.9)^2+C=-909 +C[/tex] (V)

Therefore, the potential difference is given by the difference of these two values:

[tex]\Delta V=-909 +C -C = -909 V[/tex]

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