Chapter 20: Electrodynamics

Electric Current (I)

The movement of charge through a conductor due to a potential difference. Measured in amperes (A).

Electrodynamics

The study of the causes and effects of current electricity.

Electric Circuit

A collection of components connected in a way that allows electric current to do work.

Potential Difference (V)

The work done to move a charge from one point to another, measured in volts (V).

Resistance (R)

The opposition to current flow, dependent on material and temperature, measured in ohms (Ω).

Current and Voltage

• Conventional current flows in the direction of positive charges, opposite the flow of electrons.
• Direct Current (DC): Flows in one direction.
• Alternating Current (AC): Periodically reverses direction.
• Sources of potential difference:
  • Batteries: Convert chemical energy into electrical energy.
  • Photovoltaic cells: Convert light energy into electrical energy.
  • Generators: Convert mechanical energy into electrical energy.

Ohm's Law

Formula

$V=IR$

Key Points

• Relates voltage (V), current (I), and resistance (R).
• Not all materials obey Ohm's law (e.g., diodes).

Electrical Power

Formula

$P=VI$, where P is power in watts (W).

Alternate Formulas

Using Ohm's Law:

• $P=I^{2}R$
• $P=\frac{V^2}{R}$

Applications

• Power Rating: Devices like toasters and TVs have power ratings to indicate energy use.
• Energy Cost: Calculated using power and time (e.g., kW⋅h).
• Resistors: Used to control current and voltage in circuits.

Questions for Students

1. Define electric current and its unit.
2. Explain the difference between DC and AC.
3. State and apply Ohm's law to calculate resistance in a circuit.
4. Calculate the power consumed by a 120.0 V toaster with a resistance of 15.0 Ω.
5. Explain how potential difference is created in batteries and generators.