Glossary
Charge (q)
A fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. It can be positive or negative.
Example:
An electron carries a fundamental negative charge, which dictates how it interacts with electric fields and other charged particles.
Conservation of Energy
A fundamental principle stating that the total energy of an isolated system remains constant; energy can only be transformed from one form to another, not created or destroyed.
Example:
As a charged particle speeds up in an electric field, its kinetic energy increases, but this increase is perfectly balanced by a decrease in its electric potential energy, demonstrating the principle of conservation of energy.
Coulomb (C)
The SI unit of electric charge. One coulomb is approximately the charge of 6.24 x 10^18 protons.
Example:
A lightning bolt can transfer many coulombs of charge from a cloud to 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 points in the direction a positive test charge would accelerate.
Example:
The invisible electric field around a charged comb can attract small pieces of paper, even without direct contact.
Electric Potential Difference
The change in electric potential energy per unit charge between two points in an electric field. It is measured in volts (V).
Example:
If a 12V car battery has an electric potential difference of 12 volts between its terminals, it means 12 joules of energy are available for every coulomb of charge that moves between them.
Electric Potential Energy
The energy a charged object possesses due to its position in an electric field. Changes in this energy are related to work done by or against the electric field.
Example:
When you lift a balloon charged with static electricity closer to another charged object, you are increasing its electric potential energy, similar to lifting a ball higher off the ground.
Joule (J)
The SI unit of energy and work. In electric potential energy, it represents the amount of energy transferred.
Example:
If a charge gains 20 joules of electric potential energy, it means 20 J of work was done on it by an external force, or it lost 20 J of kinetic energy.
Kinetic Energy
The energy an object possesses due to its motion. In electric systems, electric potential energy can be converted into kinetic energy.
Example:
A proton accelerating in a particle accelerator gains significant kinetic energy as it moves through large electric potential differences.
Negative Charge Movement
Negative charges accelerate from lower electric potential to higher electric potential, moving opposite to the direction of the electric field lines.
Example:
An electron in a cathode ray tube is accelerated from a negative terminal (lower potential) towards a positive screen (higher potential), demonstrating typical negative charge movement.
Positive Charge Movement
Positive charges accelerate from higher electric potential to lower electric potential, moving in the same direction as the electric field lines.
Example:
A proton released in a uniform electric field will naturally move from a region of high potential towards a region of lower potential, much like a ball rolling downhill, exhibiting positive charge movement.
Volt (V)
The SI unit of electric potential difference, defined as one joule per coulomb (J/C).
Example:
A standard AA battery provides a voltage of 1.5 volts, meaning it can provide 1.5 joules of energy for every coulomb of charge that flows through it.
Work-Energy Theorem
States that the net work done on an object equals the change in its kinetic energy. In electric fields, the work done by the field changes the kinetic energy of a charged particle.
Example:
If an electron accelerates through a potential difference, the work-energy theorem allows you to calculate its final speed by relating the work done by the electric field to the change in its kinetic energy.