Umair Gaines
In the context of electricity, 'k' often refers to Coulomb's constant, also known as the Coulomb constant, which is used in Coulomb's law. Coulomb's law, published in 1785 by French physicist Charles-Augustin de Coulomb, is an experimental law of physics that calculates the amount of force between two electrically charged particles at rest. Coulomb's constant, denoted as 'k' or 'ke', is a proportionality constant that relates the force between two charged objects to the product of their charges and the square of the distance between them. The value of Coulomb's constant is dependent on the units used for force, charge, and distance, with the SI units redefined in 2019.
| Characteristics | Values |
|---|---|
| K in Electricity | Coulomb's Constant (K) |
| Other Names | Coulomb's Law, Ke |
| Purpose | Unit conversion in Coulomb's Law |
| Units | N m2/C2 (newtons, meters, coulombs) |
| Definition of Coulomb | The amount of charge on a certain number of electrons |
| Definition of Newton | Defined in terms of the kilogram, meter, and second |
| Definition of Meter | Defined in terms of the speed of light and the second |
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What You'll Learn
Coulomb's law and Coulomb's constant
Coulomb's law, first published in 1785 by French physicist Charles-Augustin de Coulomb, is an experimental law of physics that calculates the amount of force between two electrically charged particles at rest. This electric force is conventionally called the electrostatic force or Coulomb force. Coulomb's law was essential to the development of the theory of electromagnetism and maybe even its starting point, as it allowed meaningful discussions of the amount of electric charge in a particle.
Coulomb's law states that the magnitude, or absolute value, of the attractive or repulsive electrostatic force between two point charges is directly proportional to the product of the magnitudes of their charges and inversely proportional to the square of the distance between them. Two charges can be approximated as point charges if their sizes are small compared to the distance between them. Coulomb discovered that bodies with like electrical charges repel, and oppositely charged bodies attract according to an inverse-square law.
The equation is known as Coulomb's law and describes the electrostatic force between charged objects. The constant of proportionality k in the equation is called Coulomb's constant. In SI units, the constant k has a value that determines the direction of the force along the line joining the centres of the two objects. If the two charges are of opposite signs, Coulomb's law gives a negative result, indicating an attractive force between the particles. On the other hand, if the two charges have the same sign, Coulomb's law yields a positive result, signifying a repulsive force between the particles.
Coulomb's law can be proven from Gauss's law under the assumption that the electric field from a point charge is spherically symmetric. This assumption holds exactly true if the charge is stationary and approximately true if the charge is in motion. By assuming spherical symmetry, the integrand becomes a constant that can be factored out of the integral. This constant plays a crucial role in Coulomb's law, facilitating calculations involving electric charges and providing a foundation for understanding and predicting the behaviour of electrically charged particles.
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Inverse-square law
Coulomb's law, also known as Coulomb's inverse-square law, is an experimental law of physics that calculates the amount of force between two electrically charged particles at rest. It was first published in 1785 by French physicist Charles-Augustin de Coulomb. Coulomb's law states that the magnitude or absolute value of the attractive or repulsive electrostatic force between two point charges is directly proportional to the product of the magnitudes of their charges and inversely proportional to the square of the distance between them.
The inverse-square law, in general, applies when some force, energy, or other conserved quantities are evenly radiated outward from a point source in three-dimensional space. The law states that the observed "intensity" of a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. In other words, as the distance from the source increases, the intensity decreases by the ratio of 1/r^2. This relationship is similar to that seen in gravity, magnetism, and light intensity, where the surface area of a sphere (4πr^2) is proportional to the square of the radius.
In the context of Coulomb's law, the inverse-square law describes the relationship between the force of attraction or repulsion between two electrically charged particles and the distance between them. The force is directly proportional to the product of the electric charges and inversely proportional to the square of the distance between the charges. This means that as the distance between the charges increases, the force between them decreases, following the inverse-square relationship.
The inverse-square law is also applied in various fields, such as photography and stage lighting, to determine the "fall off" or difference in illumination on a subject as it moves closer to or farther from the light source. For example, doubling the distance from the light source reduces the illumination to one-quarter of its original value. This relationship can be useful for quick approximations when calculating illumination in lighting setups.
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Electrostatic force
Coulomb's Law, an experimental law of physics, calculates the amount of force between two electrically charged particles. This law states that the magnitude or absolute value of the attractive or repulsive electrostatic force between two point charges is directly proportional to the product of the magnitudes of their charges and inversely proportional to the square of the distance between them. In other words, the force between two charged particles increases as the magnitude of their charges increases, and decreases as the distance between them increases.
The electrostatic force can be quantified using Coulomb's Law, which is expressed by the equation:
F=k\*\|(q1\*q2)/r^2\|
Where F represents the electrostatic force, k is Coulomb's constant (approximately 8.99 x 10^9 Nm^2/C^2), q1 and q2 are the magnitudes of the charges, and r is the distance between them.
The direction of the electrostatic force depends on the charges of the particles. Like charges repel each other, meaning that if both charges are positive or both are negative, the force acts away from each other. Opposite charges attract, so if one charge is positive and the other is negative, the force acts towards each other. The force always acts along the straight line connecting the two charges.
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Electric field
An electric field (sometimes called an E-field) is a physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) describes their capacity to exert attractive or repulsive forces on another charged object. Charged particles exert attractive forces on each other when the sign of their charges is opposite (one being positive and the other negative) and repel each other when the signs of the charges are the same.
The SI unit for the electric field is the volt per meter (V/m), which is equal to the newton per coulomb (N/C). The electric field is defined at each point in space as the force that would be experienced by an infinitesimally small stationary test charge at that point divided by the charge. The electric field is defined in terms of force, and force is a vector (having both magnitude and direction), so an electric field may be described by a vector field. The electric field acts between two charges similarly to the way that the gravitational field acts between two masses, as they both obey an inverse-square law with distance. This is the basis for Coulomb's law, which states that, for stationary charges, the electric field varies with the source charge and varies inversely with the square of the distance from the source.
The magnitude of the electric field around an electric charge depends on how the charge is distributed in space. For a charge concentrated at a point, the electric field is directly proportional to the amount of charge and inversely proportional to the square of the distance from the centre of the source charge. The presence of a material medium always diminishes the electric field below the value it has in a vacuum. The study of electric fields created by stationary charges is called electrostatics. Faraday's law describes the relationship between a time-varying magnetic field and the electric field.
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Newton's third law
It is important to note that collections of charged bodies do not always obey Newton's third law. For example, there can be a change in the momentum of one body without a corresponding change in the momentum of another. This discrepancy can be explained by the momentum carried by the electromagnetic field itself.
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Frequently asked questions
Coulomb's Law is an experimental law of physics that calculates the amount of force between two electrically charged particles at rest.
K, or ke, is a constant in Coulomb's Law. It must have units N m^2 / C^2.
The units in Coulomb's Law are newtons, coulombs, and meters.
K is derived from the quantities of each charge (q1 and q2) and the distance between them (r).
