Glossary
Change in Electric Potential Energy
The change in energy of a charged object when it moves between two points with different electric potentials, calculated as $\Delta U_E = q \Delta V$.
Example:
When an electron moves across a 9V battery from the negative to the positive terminal, its change in electric potential energy is negative, meaning it loses potential energy.
Charge
A fundamental property of matter that experiences a force when placed in an electromagnetic field. It can be positive or negative and is measured in Coulombs.
Example:
An electron has a negative elementary charge of approximately Coulombs.
Conservation of Energy
A fundamental principle stating that the total energy of an isolated system remains constant. Energy can transform between different forms (like potential and kinetic) but is neither created nor destroyed.
Example:
As a charged particle accelerates 'downhill' in an electric field, its decreasing electric potential energy is converted into increasing kinetic energy, demonstrating the conservation of energy.
Coulomb (C)
The SI unit of electric charge. One Coulomb is approximately the charge of $6.24 \times 10^{18}$ protons.
Example:
A lightning bolt can transfer many Coulombs of charge between the cloud and the ground in a very short time.
Electric Field
A region around a charged particle or object within which a force would be exerted on other charged particles. It is represented by field lines that point in the direction a positive test charge would move.
Example:
The space between the plates of a charged capacitor contains a uniform electric field that can accelerate charged particles.
Electric Potential Difference
The work done per unit charge to move a charge between two points in an electric field, representing the 'electric height' difference. It is measured in Volts.
Example:
A 12V car battery creates an electric potential difference of 12 volts between its terminals, driving current through the car's electrical system.
Electric Potential Energy
The energy a charged object possesses due to its position within an electric field. It is a scalar quantity and is measured in Joules.
Example:
A positive charge held near another positive charge has high electric potential energy, similar to a compressed spring ready to release energy.
Equipotential Lines
Lines or surfaces in an electric field where all points have the same electric potential. No work is done by the electric field when a charge moves along an equipotential line.
Example:
In the vicinity of a point charge, equipotential lines are concentric circles, perpendicular to the radial electric field lines.
Joule (J)
The SI unit of energy and work. It represents the energy transferred when a force of one Newton acts over a distance of one meter.
Example:
If a charge gains Joules of kinetic energy, it means that amount of work was done on it by the electric field.
Kinetic Energy
The energy an object possesses due to its motion. For a particle, it is calculated as $1/2 mv^2$.
Example:
A proton speeding up as it moves from a high potential to a low potential in an electric field gains kinetic energy.
Volt (V)
The SI unit of electric potential difference, defined as one Joule per Coulomb (J/C).
Example:
A standard AA battery provides about 1.5 Volts of potential difference, meaning 1.5 Joules of energy are available per Coulomb of charge.