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Electric Field Lines - Definition, Properties, Attraction, FAQs

Electric Field Lines - Definition, Properties, Attraction, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:01 PM IST

How to define a field or simply what does a field mean? ‘Field’ is a term referring to a quantity that is defined at every point in a space. The electric field at a point in the space around a charge or a system of charges gives us the force that a unit-positive test charge would experience, if it is placed at that point, without disturbing the system. Now, the work of the electric field lines is to map this electric field around a charge or a configuration of charges pictorially. So in this article, we will discuss what are electric field lines, electric field lines attraction and repulsion, properties of electric field lines class 12, rules for drawing electric field lines, electric field around a point charge, electric field between two-point charges, and differential equation of electric field lines and solved problems based on that.

This Story also Contains
  1. Physical Significance of Electric Field
  2. What are Electric Field Lines Class 12?
  3. Electric Field Lines Attraction And Repulsion
  4. Properties of Electric Field Lines Class 12
  5. Rules For Drawing Electric Field Lines
  6. Electric Field Around a Point Charge
  7. Electric Field Between Two-Point Charges
  8. Differential Equations for Electric Force Lines/Electric Field Lines
  9. Solved Examples Based On Electric Field Lines
Electric Field Lines - Definition, Properties, Attraction, FAQs
Electric Field Lines - Definition, Properties, Attraction, FAQs

Physical Significance of Electric Field

As we have already discussed the electric field at a point in space around a system /configuration of electric charges tells us how a unit positive test charge would experience force at that particular point. Now, this field does not depend on the test charge we use to determine the electric field at that particular point. So we can say that by knowing the electric field at any point in space, we can calculate the magnitude and direction of force experienced by a unit test charge at that particular point. The direction of the electric field is outwards from a positive charge and it is directed inwards in case of a negative charge. Let $E$ be the electric field intensity at a point $\mathbf{r}$ and $q_0$ is the test charge, then $\mathbf{F}(\mathbf{r})=q_0 \mathbf{E}(\mathbf{r})$.This is the physical significance of the electric field.

What are Electric Field Lines Class 12?

Electric field lines definition: Electric field lines are the imaginary lines that signify the direction and strength of an electric field. The electric field lines are discovered by Michael Faraday. Electric field lines are nothing but the path along which a unit positive charge will move if it is placed there and allowed to be free to move.

An electric field around a charge or a configuration of charges can be mapped pictorially using the electric field lines, also called the electric lines of forces. It is a mathematical way of visualizing electric fields around a charge or a system of charges placed in a particular configuration. However, for electric field lines definition, we can define an electric field line as a path, which can be curved or straight, in an electric field, such that tangent to it at any point gives us the direction of the electric field at that point.

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The figure given below is an electrostatic line of force. The tangent to the line at point P gives us the direction of the electric field $E_{p}$ and similarly, the tangent to the curved line at point R gives us the direction of the electric field intensity.

Tangent to a point on an electric field line gives direction of the electric field.

(Fig-1)

Thus, electric field lines provide information about the direction of electric field intensity at a point. Also, the magnitude of the electric field is represented by the density of field lines or the number of electric lines of force in that region. The denser the region with field lines; the greater the magnitude of electric field intensity at that region. Note that these field lines are in all three dimensions.

Electric Field Lines Attraction And Repulsion

  • The figure shows electric field lines/lines of forces due to a single positive charge. Note the direction of electric field lines. These lines for a single positive point charge are directed radially outwards and extend up to infinity.

Electric field lines radiate outwards in case of single positive point charge

However, in the case of a single negative point charge, the electric field lines are always directed radially inwards.

single negative point charge

  • The figure below shows the electric field lines for a pair of equal and opposite charges, also called an electric dipole. Note the direction of the electric field, it goes from positive to negative charge. These electric field lines show that there is a mutual attraction between the two opposite charges. Hence these are the attractive field lines between the charges.

pair of equal and opposite charges

  • The figure given below shows electric field lines for opposite and unequal charges. The electric field lines are always denser towards the charge having a larger magnitude.

electric field lines for opposite and unequal charges

  • The figure given below shows electric field lines due to two equal positive charges. These field lines are repulsive. These lines exert lateral pressure on each other and this results in repulsion between the charges. Also, note that there is a neutral point exactly at the middle (point M) where net electric field intensity is equal to zero.

Electric field lines

  • Similarly, electric field lines are due to two equal negative charges.

shows electric field lines due

  • This neutral point shifts from the center position if the charges are unequal where this neutral point is closer to the smaller charge

Electric Field Patterns for Object

  • Some other miscellaneous cases such as the representation of the field lines due to 2 equal positively charged rods normal to the page and due to two rods of linear charge density 2 and $-\lambda$ respectively, normal to the page.

Notice the box, it represents the neutral point at the center

The box denotes the neutral point where the electric field is zero.

As the rods have unequal charge density, the neutral point is not present at the center

Properties of Electric Field Lines Class 12

The properties of electric field lines are-

  1. Electric field lines are always continuous. They are continuous curves but they do not form loops. They start from a positive charge or a positively charged body and end at a negative charge or a negatively charged body. In the case of a single positive and negative charge, the electric field lines end or start at infinity.

  2. The tangent to an electric field line at any point gives us the direction of the electric field at that particular point.

  3. Two electric field lines of force never intersect with each other. The reason behind this is, that if two lines intersect with each other, then at that intersecting point, we can draw 2 tangents which will give two directions of electric fields $E_1$ and $E_2$ which is not possible. Hence, two electric field lines will never intersect with each other.

Two electric field lines of force

  1. The electric field lines exert a lateral pressure in case of repulsion between like charges.

  2. The electric field lines contract longitudinally in case of attraction between opposite charges.

  3. No component of the electric field is parallel to the surface of the conductor. They are always perpendicular to the surface of a conductor.

Electric field lines on a conductor are always perpendicular at its surface.

Rules For Drawing Electric Field Lines

  1. The electric field lines direct away from positive charges and towards negative charges.
  2. The electric field lines begin on positive charges and end on negative charges.
  3. If there is no end opposite charge, they end at infinity
  4. The electric field lines should never cross each other
  5. No closed loop because electric field lines don't form closed loops
  6. The lines are closer when the field is stronger

Electric Field Around a Point Charge

The electric field around a point charge is experienced in a region around a charge where it exerts force on other charges. The magnitude of the charge and the distance from the charge are the two factors affecting the field strength. The electric field at a distance $r$ of a point charge $q$ is

$$
E=\frac{k|Q|}{r^2}
$$

where,

$E$ is the electric field strength
$Q$ is the magnitude of the point charge
$r$ is the distance from the charge
$k$ is the coulomb's constant

Electric Field Between Two-Point Charges

If the electric field at a point due to $Q_1$ is $E_1=\frac{k\left|Q_1\right|}{r_1^2}$ and due to $Q_2$ is $E_2=\frac{k\left|Q_2\right|}{r_2^2}$, then the total electric field $E$ at that point is:

$$
E=E_1+E_2=\frac{k\left|Q_1\right|}{r_1^2}+\frac{k\left|Q_2\right|}{r_2^2}
$$

where,

$E$ is the total electric field at the point
$r_1$ is the distance from $Q_1$ to the point
$r_2$ is the distance from $Q_2$ to the point
$k$ is the coulomb's constant

Differential Equations for Electric Force Lines/Electric Field Lines

Suppose $\mathbf{r}=\mathbf{r}(s)$ represents the force lines. Then, $\frac{d \mathbf{r}}{d s}$ will represent the tangent to the force line at every point. Since the tangent to the curve at any point represents the direction of the electric field, therefore,

$$
\frac{d \mathbf{r}}{d s}=\alpha \mathbf{E}(\mathbf{r})
$$

$
\text { where } \alpha \text { is a constant. }
$

$\begin{gathered}\frac{d x}{d s}=\alpha E_x, \quad \frac{d y}{d s}=\alpha E_y, \quad \frac{d z}{d s}=\alpha E_z \\ \frac{d x}{E_x}=\frac{d y}{E_y}=\frac{d z}{E_z}\end{gathered}$

This is the differential equation for electric field lines.

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Solved Examples Based On Electric Field Lines

Example 1: A long cylindrical shell carries a positive surface charge $\sigma$ in the upper half and a negative surface charge $-\sigma$ in the lower half. The electric field lines around the cylinder will look like the figure given in : (figures are schematic and not drawn to scale)

1)

2)

3)

4)

Solution:

Direction of Electric field -Due to a Positive Charge electric field is always away from the charge.

Direction of Electric field

Due to the Negative charge electric field is always towards the charge.

The electric field lines around the cylinder must resemble that due to the dipole.

Example 2: Charges are placed on the vertices of a square as shown. Let {E}$ be the electric field and V the potential at the center. If the charges on A and B are interchanged with those on D and C respectively, then

1) $\vec{E}$ changes, V remains unchanged

2) $\vec{E}$ remains unchanged $V$ changes

3) both $\vec{E}$ and $V$ change

4) both $\vec{E}$ and $V$ are unchanged

Solution:

Direction of Electric field

Due to the Positive Charge electric field is always away from the charge.

Direction of Electric field

Due to the Negative charge electric field is always towards the charge.

"Unit positive charge" will be repelled by A and B and attracted by -q and -q downwards in the same direction. If they are exchanged the direction of the field will be opposite. In the case of potential, as it is a scalar, they cancel each other whatever may be their position.

$\therefore$ The field is affected but not the potential.

Example 3: A charged particle is free to move in an electric field. It will travel

1) Always along a line of force

2) Along a line of force, if its initial velocity is zero

3) Along a line of force, if it has some initial velocity in the direction of an acute angle with the line of force

4) None of the above

Solution:

Because E points along the tangent to the lines of force. If the initial velocity is zero, then due to the force, it always moves in the direction of $E$. Hence it will always move on some lines of force.

Hence, the answer is the option (2).

Example 4: A metallic solid sphere is placed in a uniform electric field. The lines of force follow the path(s) shown in the figure as

1) 1

2) 2

3) 3

4) 4

Solution:

Direction of Electric field

Due to the Positive Charge electric field is always away from the charge.

The electric field is always perpendicular to the surface of a conductor. On the surface of a metallic solid sphere, the electrical field is oriented normally (i.e. directed towards the center of the sphere).

Example 5: Electric lines of force about negative point charge are

1) Circular, anticlockwise

2) Circular, clockwise

3) Radial, inward

4) Radial, outward

Solution:

Direction of Electric field

Due to the Positive Charge electric field is always away from the charge.

Electric lines' force due to negative charge is radially inward.

Frequently Asked Questions (FAQs)

1. Write one difference between electric field lines and magnetic field lines.

Magnetic field lines and electric field lines, both are continuous but electric field lines do not form closed loops. However, magnetic field lines can form closed loops.

2. Why are electric field lines continuous and cannot have sudden breaks?

 In an electrostatic field, a charge experiences a continuous force and hence it moves continuously. If the electric field will have sudden breaks, it will mean that a charge will jump from one point to another point which is not possible.

3. When is an electric field line straight?

Electric field line is straight for a single charge.

4. Why do we get a neutral point in the space between two like charges?

This reason behind this is because the net electric field is zero at that point as the field intensities due to the two charges are equal and opposite at that point.

5. What is the physical significance of electric field lines?

Tangent to electric  field lines at any point gives the direction of electric field and the higher is the density of electric field lines, the higher is the magnitude of electric field intensity at that region.

6. Why are electric field lines always perpendicular to equipotential surfaces?
Electric field lines are always perpendicular to equipotential surfaces because the electric field points in the direction of the steepest decrease in electric potential. Since equipotential surfaces connect points of equal potential, the direction of steepest potential change must be perpendicular to these surfaces.
7. What is the relationship between electric field lines and equipotential surfaces?
Electric field lines are always perpendicular to equipotential surfaces. This is because the electric field represents the direction of maximum change in potential, while equipotential surfaces connect points of equal potential. The perpendicular relationship ensures that no work is done when moving along an equipotential surface.
8. How do electric field lines behave in a uniform electric field?
In a uniform electric field, such as the field between two large, parallel charged plates, the electric field lines are parallel, equally spaced, and have the same strength throughout the region. This represents a constant electric field strength and direction across the entire area.
9. How do electric field lines behave at the interface between two different dielectric materials?
At the interface between two different dielectric materials, electric field lines bend or refract. This bending occurs due to the change in the electric field strength in the two materials, which have different permittivities. The field lines are always continuous across the boundary but change direction.
10. How do electric field lines represent the concept of electric flux?
Electric flux is represented by the number of electric field lines passing through a given surface area. More lines passing through a surface indicate greater flux. The concept of flux is crucial in understanding Gauss's law and the behavior of electric fields in different geometries.
11. How do electric field lines behave around a point charge?
For a point charge, electric field lines radiate outward in all directions if the charge is positive, or inward from all directions if the charge is negative. The lines are straight and extend radially to or from infinity, with their density decreasing as distance from the charge increases.
12. What is the relationship between the number of electric field lines and the magnitude of the charge?
The number of electric field lines originating from or terminating on a charge is proportional to the magnitude of the charge. A larger charge will have more field lines associated with it, while a smaller charge will have fewer lines. This relationship helps visualize the relative strengths of different charges.
13. What does the convergence or divergence of electric field lines indicate?
The convergence of electric field lines (lines coming closer together) indicates an increase in field strength and often points towards a negative charge. Divergence of field lines (lines spreading apart) indicates a decrease in field strength and often originates from a positive charge. These patterns help visualize the spatial variation of electric field strength.
14. What does the spacing between electric field lines tell us?
The spacing between electric field lines provides information about the strength of the electric field. Closely spaced lines indicate a strong electric field, while widely spaced lines indicate a weak electric field. This relationship allows for a visual representation of field strength variations.
15. How do electric field lines represent the concept of electric field discontinuity?
Electric field discontinuities are represented by abrupt changes in the density or direction of electric field lines. These discontinuities typically occur at the interface between different materials or at the surface of charged conductors. The field lines may change direction or density sharply at these boundaries.
16. How do electric field lines represent the force between two like charges?
For two like charges (both positive or both negative), the electric field lines emerge from both charges and repel each other, curving away in the space between them. This pattern visualizes the repulsive force between like charges, as the field lines "push" away from each other.
17. How do electric field lines represent the force between two unlike charges?
For two unlike charges (one positive and one negative), the electric field lines start from the positive charge and end on the negative charge. The lines curve towards each other in the space between the charges, visualizing the attractive force between unlike charges.
18. How do electric field lines behave around an electric dipole?
For an electric dipole (a pair of equal and opposite charges close together), the electric field lines emerge from the positive charge and curve around to enter the negative charge. The field is strongest between the charges and weakens with distance, forming a characteristic dipole field pattern.
19. What does it mean when electric field lines are parallel?
Parallel electric field lines indicate a uniform electric field. In such a field, the strength and direction of the electric field are constant throughout the region. This situation is approximately true between two large, oppositely charged parallel plates, far from the edges.
20. How do electric field lines represent superposition of fields from multiple charges?
When multiple charges are present, the resulting electric field lines represent the superposition of the individual fields. The lines will be denser where the fields add constructively and less dense where they partially cancel. The direction of the lines at any point represents the net field direction.
21. How do electric field lines represent the principle of superposition for electric fields?
The principle of superposition for electric fields is represented by the combination of electric field lines from multiple charges. Where fields from different charges reinforce each other, the lines become denser. Where they oppose each other, the lines become sparser or may even cancel out. The resulting pattern shows the net electric field at each point.
22. How do electric field lines represent the concept of electric dipole moment?
Electric field lines for an electric dipole form a characteristic pattern that represents the dipole moment. The lines emerge from the positive charge, curve around, and enter the negative charge. The strength and extent of this pattern reflect the magnitude of the dipole moment, which depends on both the charge separation and the charge magnitude.
23. How do electric field lines behave in the presence of a grounded conductor?
When a grounded conductor is present in an electric field, the field lines will terminate on the conductor's surface. The conductor acquires an induced charge distribution that reshapes the electric field around it. No field lines penetrate the conductor, as its interior remains at zero potential.
24. How do electric field lines represent the concept of electric field shielding?
Electric field shielding is represented by the absence of electric field lines inside a closed conductor. The field lines terminate on the outer surface of the conductor, and no lines penetrate its interior. This visualization demonstrates how a Faraday cage works to shield its interior from external electric fields.
25. How do electric field lines behave in the presence of a perfect conductor?
In the presence of a perfect conductor, electric field lines always meet the surface at right angles. Inside the conductor, there are no electric field lines as the field is zero. Any external field causes a redistribution of charges on the conductor's surface to cancel the field inside, a phenomenon known as electrostatic shielding.
26. What is the significance of the number of electric field lines entering or leaving a closed surface?
The number of electric field lines entering or leaving a closed surface is proportional to the net charge enclosed by that surface. This concept is directly related to Gauss's law, which states that the electric flux through a closed surface is proportional to the enclosed charge.
27. What does the absence of electric field lines in a region tell us?
The absence of electric field lines in a region indicates that the electric field strength is zero in that area. This can occur inside a conductor in electrostatic equilibrium, in regions where fields from multiple charges cancel out, or at points of symmetry in certain charge distributions where the net field is zero.
28. Can electric field lines ever be parallel to equipotential surfaces?
No, electric field lines can never be parallel to equipotential surfaces. They are always perpendicular to equipotential surfaces. This is because the electric field points in the direction of the steepest decrease in potential, which is necessarily perpendicular to surfaces of constant potential.
29. How do electric field lines represent the concept of electric field singularities?
Electric field singularities are represented by points where electric field lines converge or diverge infinitely. These typically occur at point charges or sharp edges of conductors. In reality, perfect singularities don't exist due to quantum effects and material limitations, but the concept is useful for understanding field behavior near highly concentrated charges.
30. Can electric field lines ever be discontinuous?
Electric field lines themselves are continuous, but their density or direction can change abruptly at boundaries between different materials or at surfaces of charge distributions. These abrupt changes represent discontinuities in the electric field strength or direction, which are important in understanding field behavior at interfaces.
31. What is the significance of the tangent to an electric field line at any point?
The tangent to an electric field line at any point gives the direction of the electric field vector at that point. This means that if you were to place a positive test charge at that location, it would experience a force in the direction of the tangent to the field line.
32. How do electric field lines represent field strength?
The strength of an electric field is represented by the density of electric field lines in a given area. Where the lines are closer together, the field is stronger. Where the lines are farther apart, the field is weaker. This relationship allows us to visualize variations in field strength across space.
33. Can electric field lines start or end in empty space?
No, electric field lines cannot start or end in empty space. They must always begin on positive charges and end on negative charges, or extend to infinity. This property reflects the fact that electric charges are the sources and sinks of electric fields.
34. How do electric field lines behave inside a hollow conductor?
Inside a hollow conductor, there are no electric field lines. The electric field inside a conductor in electrostatic equilibrium is always zero, regardless of the external field. This is known as electrostatic shielding and is the basis for Faraday cages.
35. Can electric field lines ever be curved in a region of constant electric field?
No, in a region of constant electric field, the electric field lines are always straight and parallel. Curved field lines indicate a changing direction of the electric field, which is not the case in a constant field. Curved lines are typically seen around point charges or in complex charge distributions.
36. Why do electric field lines never cross each other?
Electric field lines never cross because the electric field has a unique direction at any given point. If two lines were to cross, it would imply that the electric field has two different directions at that point, which is impossible. This property ensures that the electric field is well-defined everywhere in space.
37. Can electric field lines form closed loops?
No, electric field lines cannot form closed loops. They always start from positive charges and end on negative charges, or extend to infinity. Closed loops would violate the conservative nature of electrostatic fields, as they would imply that a charge could gain energy by moving in a complete circuit, which is not possible in electrostatics.
38. What happens to electric field lines at the surface of a conductor?
Electric field lines always meet the surface of a conductor at right angles. This is because any component of the electric field parallel to the surface would cause charges to move, which doesn't occur in electrostatic equilibrium. Inside a conductor, the electric field is zero, so no field lines exist there.
39. What does the direction of an electric field line indicate?
The direction of an electric field line at any point indicates the direction of the electric force that would act on a positive test charge placed at that point. By convention, the arrows on field lines point in the direction a positive charge would move if placed in the field.
40. How do electric field lines behave at sharp points or edges of a conductor?
Electric field lines concentrate at sharp points or edges of a conductor, resulting in a higher density of field lines in these regions. This concentration indicates a stronger electric field near sharp points or edges, a phenomenon known as the "edge effect" or "point effect."
41. What are electric field lines?
Electric field lines are imaginary lines used to visualize the electric field around charged objects. They show the direction of the electric force experienced by a positive test charge placed in the field. The lines start from positive charges and end on negative charges, or extend to infinity for isolated charges.
42. What does the density of electric field lines tell us about the rate of change of electric potential?
The density of electric field lines is directly related to the rate of change of electric potential. Where the field lines are dense, the potential changes rapidly with distance, indicating a strong electric field. Where the lines are sparse, the potential changes more gradually, indicating a weaker field. This relationship helps visualize the spatial variation of electric potential.
43. How do electric field lines represent the concept of electric field gradient?
The electric field gradient is represented by the change in density or direction of electric field lines. A rapid change in the spacing or orientation of field lines indicates a large field gradient. This concept is important in understanding how the electric field varies in space and is crucial in many practical applications of electrostatics.
44. What does the symmetry of electric field lines tell us about the charge distribution?
The symmetry of electric field lines reflects the symmetry of the underlying charge distribution. For example, spherically symmetric field lines indicate a spherically symmetric charge distribution, while cylindrically symmetric field lines suggest a cylindrically symmetric charge arrangement. This relationship helps in inferring charge distributions from field patterns.
45. Can electric field lines ever form loops or circles?
In electrostatics, electric field lines cannot form loops or circles. This is because electrostatic fields are conservative, meaning the work done in moving a charge around a closed path is zero. Looped field lines would violate this principle. However, in time-varying magnetic fields, induced electric fields can form closed loops.
46. How do electric field lines behave around a charged infinite plane?
For a charged infinite plane, the electric field lines are perpendicular to the plane and extend outward on both sides. The field lines are parallel and equally spaced, indicating a uniform electric field. The field strength is constant on each side of the plane but may differ in magnitude if the plane is asymmetrically charged.
47. Can electric field lines ever form right angles with each other?
Electric field lines cannot form right angles with each other in free space. However, they can meet at right angles when they intersect a conducting surface. This is because the electric field must be perpendicular to the surface of a conductor in electrostatic equilibrium.
48. Can electric field lines ever be tangent to a conducting surface?
No, electric field lines cannot be tangent to a conducting surface in electrostatic equilibrium. They must always meet the surface at right angles. Any tangential component would cause charges to move along the surface, violating the condition of electrostatic equilibrium.
49. Can electric field lines ever intersect or touch each other?
No, electric field lines can never intersect or touch each other. If they did, it would mean that at the point of intersection, the electric field has two different directions simultaneously, which is physically impossible. Each point in space has a unique electric field vector associated with it.
50. How do electric field lines behave around a charged spherical shell?
For a charged spherical shell, the electric field lines are radial and extend outward from the surface if the shell is positively charged, or inward if negatively charged. Outside the shell, the field behaves as if all the charge were concentrated at the center. Inside the shell, there are no field lines, as the electric field is zero.
51. How do electric field lines behave around a system of many point charges?
For a system of many point charges, the electric field lines represent the superposition of fields from all charges. The lines start from positive charges and end on negative charges, or extend to infinity. The pattern can be complex, with lines clustering where fields add constructively and spreading where they partially cancel.
52. How do electric field lines behave in the presence of a dielectric material?
In the presence of a dielectric material, electric field lines are altered. They become more concentrated within the dielectric due to polarization effects. At the boundary between the dielectric and surrounding medium, the field lines bend due to the change in permittivity. This bending follows Snell's law for electric fields.
53. What does the curvature of electric field lines tell us about the field?
The curvature of electric field lines provides information about how the direction of the electric field changes in space. Straight lines indicate a uniform field direction, while curved lines show that the field direction is changing. The degree of curvature can indicate how rapidly the field direction is changing in a given region.
54. How do electric field lines represent the concept of electric field energy density?
The energy density of an electric field is related to the square of the field strength. In terms of field lines, regions with a higher density of lines have a higher energy density. This concept is important in understanding the energy stored in electric fields and its relevance in various electromagnetic phenomena.
55. Can electric field lines ever start or end on uncharged objects?
Electric field lines cannot start or end on truly uncharged objects. However, they can appear to do so on polarized objects or induced charge distributions. In these cases, the lines are actually starting and ending on the separated charges within the object, even though the object as a whole remains neutral.

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