Point charge

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A point charge is an idealized model in physics where a charge is concentrated at a single point with no dimensions. It generates an electric field that radiates uniformly outward, decreasing in strength with the square of the distance.

>Model

ID:(2074, 0)



Mechanisms

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Code
Concept

Mechanisms

ID:(15793, 0)



Particle in electric field of point charge

Concept

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In the case of a spherical Gaussian surface, the electric field ($\vec{E}$) is constant in the direction of the versor normal to the section ($\hat{n}$). Therefore, using the charge ($Q$), the electric field constant ($\epsilon_0$), and the dielectric constant ($\epsilon$), it can be calculated by integrating over the surface where the electric field is constant ($dS$):

$\displaystyle\int_S\vec{E}\cdot\hat{n}\,dS=\displaystyle\frac{Q}{\epsilon_0\epsilon}$



with the surface ($S$) for a sphere of radius a distance between charges ($r$):

$ S = 4 \pi r ^2$





Thus, the electric field of a point charge ($E_p$) results in:

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$

ID:(11835, 0)



Particle in electric potencial of point charge

Concept

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The electric potential, point charge ($\varphi_p$) is calculated from the radial integration of the electric field of a point charge ($E_p$) from the radius ($r$) to infinity, which results in

$ \varphi_p = -\displaystyle\int_r^{\infty} du\,E_p$



On the other hand, for the charge ($Q$), the dielectric constant ($\epsilon$), and the electric field constant ($\epsilon_0$), the value of the electric field of a point charge ($E_p$) is

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$



This implies that by integrating

$\varphi_p = -\displaystyle\int_{r}^{\infty} du \displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon u^2 }= -\displaystyle\frac{ Q }{ 4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r }$



we obtain

$ \varphi_p = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r } $



As illustrated in the following graph:



the field at two points must have the same energy. Therefore, the variables the charge ($Q$), the particle mass ($m$), the speed 1 ($v_1$), the speed 2 ($v_2$), and the electric potential 1 ($\varphi_1$) according to the equation:

$ \varphi_1 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_1 } $



and the electric potential 2 ($\varphi_2$), according to the equation:

$ \varphi_2 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_2 } $



must satisfy the following relationship:

$ \displaystyle\frac{1}{2} m v_1 ^2 + q \varphi_1 = \displaystyle\frac{1}{2} m v_2 ^2 + q \varphi_2 $

ID:(11842, 0)



Model

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Parameters

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$\epsilon$
epsilon
Dielectric constant
-
$\epsilon_0$
epsilon_0
Electric field constant
C^2/m^2N
$m$
m
Particle mass
kg
$\pi$
pi
Pi
rad

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$Q$
Q
Charge
C
$E_{p1}$
E_p1
Electric field of a point charge in 1
V/m
$E_{p2}$
E_p2
Electric field of a point charge in 2
V/m
$\varphi_1$
phi_1
Electric potential 1
V
$\varphi_2$
phi_2
Electric potential 2
V
$r_1$
r_1
Radius 1
m
$r_2$
r_2
Radius 2
m
$v_1$
v_1
Speed 1
m/s
$v_2$
v_2
Speed 2
m/s
$q$
q
Test charge
C

Calculations


First, select the equation: to , then, select the variable: to

Calculations

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

Variable Given Calculate Target : Equation To be used




Equations

#
Equation

$ E_{p1} =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r_1 ^2}$

E_p = Q /(4 * pi * epsilon_0 * epsilon * r ^2)


$ E_{p2} =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r_2 ^2}$

E_p = Q /(4 * pi * epsilon_0 * epsilon * r ^2)


$ \displaystyle\frac{1}{2} m v_1 ^2 + q \varphi_1 = \displaystyle\frac{1}{2} m v_2 ^2 + q \varphi_2 $

m * v_1 ^2/2 + q * phi_1 = m * v_2 ^2/2 + q * phi_2


$ \varphi_1 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_1 } $

phi_p = - Q /(4 * pi * epsilon * epsilon_0 * r )


$ \varphi_2 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_2 } $

phi_p = - Q /(4 * pi * epsilon * epsilon_0 * r )

ID:(15803, 0)



Point charge (1)

Equation

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The electric field of a point charge ($E_p$) is a function of the charge ($Q$), the electric field constant ($\epsilon_0$), the dielectric constant ($\epsilon$), and the distance between charges ($r$) and is calculated as follows:

$ E_{p1} =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r_1 ^2}$

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$

$Q$
Charge
$C$
5459
$\epsilon$
Dielectric constant
$-$
5463
$r$
$r_1$
Radius 1
$m$
10390
$\epsilon_0$
Electric field constant
8.854187e-12
$C^2/m^2N$
5462
$E_p$
$E_{p1}$
Electric field of a point charge in 1
$V/m$
10474
$\pi$
Pi
3.1415927
$rad$
5057

In the case of a spherical Gaussian surface, the electric field ($\vec{E}$) is constant in the direction of the versor normal to the section ($\hat{n}$). Therefore, using the charge ($Q$), the electric field constant ($\epsilon_0$), and the dielectric constant ($\epsilon$), it can be calculated by integrating over the surface where the electric field is constant ($dS$):

$\displaystyle\int_S\vec{E}\cdot\hat{n}\,dS=\displaystyle\frac{Q}{\epsilon_0\epsilon}$



with the surface ($S$) for a sphere of radius a distance between charges ($r$):

$ S = 4 \pi r ^2$



Thus, the electric field of a point charge ($E_p$) results in:

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$

ID:(11442, 1)



Point charge (2)

Equation

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The electric field of a point charge ($E_p$) is a function of the charge ($Q$), the electric field constant ($\epsilon_0$), the dielectric constant ($\epsilon$), and the distance between charges ($r$) and is calculated as follows:

$ E_{p2} =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r_2 ^2}$

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$

$Q$
Charge
$C$
5459
$\epsilon$
Dielectric constant
$-$
5463
$r$
$r_2$
Radius 2
$m$
10391
$\epsilon_0$
Electric field constant
8.854187e-12
$C^2/m^2N$
5462
$E_p$
$E_{p2}$
Electric field of a point charge in 2
$V/m$
10475
$\pi$
Pi
3.1415927
$rad$
5057

In the case of a spherical Gaussian surface, the electric field ($\vec{E}$) is constant in the direction of the versor normal to the section ($\hat{n}$). Therefore, using the charge ($Q$), the electric field constant ($\epsilon_0$), and the dielectric constant ($\epsilon$), it can be calculated by integrating over the surface where the electric field is constant ($dS$):

$\displaystyle\int_S\vec{E}\cdot\hat{n}\,dS=\displaystyle\frac{Q}{\epsilon_0\epsilon}$



with the surface ($S$) for a sphere of radius a distance between charges ($r$):

$ S = 4 \pi r ^2$



Thus, the electric field of a point charge ($E_p$) results in:

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$

ID:(11442, 2)



Electrical potentials, point charge (1)

Equation

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The electric potential, point charge ($\varphi_p$) is with the charge ($Q$), the distance between charges ($r$), the dielectric constant ($\epsilon$) and the electric field constant ($\epsilon_0$) equal to:

$ \varphi_1 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_1 } $

$ \varphi_p = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r } $

$Q$
Charge
$C$
5459
$\epsilon$
Dielectric constant
$-$
5463
$r$
$r_1$
Radius 1
$m$
10390
$\epsilon_0$
Electric field constant
8.854187e-12
$C^2/m^2N$
5462
$\varphi_p$
$\varphi_1$
Electric potential 1
$V$
10392
$\pi$
Pi
3.1415927
$rad$
5057

The electric potential, point charge ($\varphi_p$) is calculated from the radial integration of the electric field of a point charge ($E_p$) from the radius ($r$) to infinity, which results in

$ \varphi_p = -\displaystyle\int_r^{\infty} du\,E_p$



On the other hand, for the charge ($Q$), the dielectric constant ($\epsilon$), and the electric field constant ($\epsilon_0$), the value of the electric field of a point charge ($E_p$) is

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$



This implies that by integrating

$\varphi_p = -\displaystyle\int_{r}^{\infty} du \displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon u^2 }= -\displaystyle\frac{ Q }{ 4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r }$



we obtain

$ \varphi_p = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r } $

ID:(11576, 1)



Electrical potentials, point charge (2)

Equation

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The electric potential, point charge ($\varphi_p$) is with the charge ($Q$), the distance between charges ($r$), the dielectric constant ($\epsilon$) and the electric field constant ($\epsilon_0$) equal to:

$ \varphi_2 = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r_2 } $

$ \varphi_p = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r } $

$Q$
Charge
$C$
5459
$\epsilon$
Dielectric constant
$-$
5463
$r$
$r_2$
Radius 2
$m$
10391
$\epsilon_0$
Electric field constant
8.854187e-12
$C^2/m^2N$
5462
$\varphi_p$
$\varphi_2$
Electric potential 2
$V$
10393
$\pi$
Pi
3.1415927
$rad$
5057

The electric potential, point charge ($\varphi_p$) is calculated from the radial integration of the electric field of a point charge ($E_p$) from the radius ($r$) to infinity, which results in

$ \varphi_p = -\displaystyle\int_r^{\infty} du\,E_p$



On the other hand, for the charge ($Q$), the dielectric constant ($\epsilon$), and the electric field constant ($\epsilon_0$), the value of the electric field of a point charge ($E_p$) is

$ E_p =\displaystyle\frac{1}{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{Q}{ r ^2}$



This implies that by integrating

$\varphi_p = -\displaystyle\int_{r}^{\infty} du \displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon u^2 }= -\displaystyle\frac{ Q }{ 4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r }$



we obtain

$ \varphi_p = -\displaystyle\frac{ Q }{4 \pi \epsilon_0 \epsilon }\displaystyle\frac{1}{ r } $

ID:(11576, 2)



Energy of a particle

Equation

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Electric potentials, which represent potential energy per unit of charge, influence how the velocity of a particle varies. Consequently, due to the conservation of energy between two points, it follows that in the presence of variables the charge ($q$), the particle mass ($m$), the speed 1 ($v_1$), the speed 2 ($v_2$), the electric potential 1 ($\varphi_1$), and the electric potential 2 ($\varphi_2$), the following relationship must be satisfied:

$ \displaystyle\frac{1}{2} m v_1 ^2 + q \varphi_1 = \displaystyle\frac{1}{2} m v_2 ^2 + q \varphi_2 $

$\varphi_1$
Electric potential 1
$V$
10392
$\varphi_2$
Electric potential 2
$V$
10393
$m$
Particle mass
$kg$
5516
$v_1$
Speed 1
$m/s$
8562
$v_2$
Speed 2
$m/s$
8563
$q$
Test charge
$C$
8746

ID:(11596, 0)