University:
The University Of Western Ontario
Course:
Physics 3400B | Introduction to Thermal Physics
Academic year:

2024
Views:

341

Pages:

2
Author:

Kyuwon J.

1 Potential Energy (General Concept) • Definition: Potential energy is stored energy due to an object’s position or configuration. • Exists in different forms: – Gravitational Potential Energy: Stored energy due to height in a gravitational field. – Elastic Potential Energy: Stored energy in a stretched or compressed object (e.g., spring, rubber band). – Electrical Potential Energy: Stored energy due to charge positions in an electric field. • General rule: Potential energy increases when work is done against a force field, and decreases when moving naturally within the field. 2 Electrical Potential Energy (U ) • Definition: The energy stored in a charge due to its position in an electric field. • Formula: U =k q1 q2 r – k = 9.0 × 109 Nm2 /C2 (Coulomb’s constant). – q1 , q2 = charges involved. – r = distance between the charges. • How it changes: – Like charges (+,+) or (-,-) → More energy when closer (work is required to push them together). – Opposite charges (+,-) → More energy when farther apart (work is required to separate them). – If a charge moves naturally in a field, it loses potential energy. – If a charge is pushed against the field, it gains potential energy. 3 Voltage (Electric Potential, V ) • Definition: Voltage is the amount of energy per unit charge. • Formula: V = 1 U q – V = Electric potential (Volts). – U = Electrical potential energy (Joules). – q = Charge (Coulombs). • Key Idea: – Voltage is NOT total energy—it measures how much energy each charge has. – Higher voltage means more energy per charge. – Charges move from high voltage to low voltage, just like water flows downhill. 4 Difference Between Potential Energy, Electrical Potential Energy, and Voltage • Potential Energy: Any stored energy due to position. • Electrical Potential Energy: Stored energy in charges due to electric fields. • Voltage (Electric Potential): Energy per charge, measured in Volts. 5 Water Slide Analogy • Voltage is like the height of the slide. • Electrical potential energy is like the total energy of the water. • If the slide is higher (higher voltage), each drop of water (each charge) has more energy. 6 Equation for Electrical Potential Energy Change • When a charge moves, its energy changes: ∆U = q∆V – ∆U = Change in electrical potential energy. – q = Charge (Coulombs). – ∆V = Voltage difference. • Example: A 2C charge moves through a 5V difference: ∆U = (2C)(5V ) = 10J • If the charge moves naturally, it loses 10J. • If we push it against the field, it gains 10J. 2

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