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ch 22 sec 1_Current_and_Circuits w 8 tr 2

Electric Current and Circuits

Understanding Electric Current

  • Definition: Electric current is the flow of electric charges through a conductor.

  • Flow of Charges: When two conductors touch, charges flow from the one at higher potential to the lower potential until equilibrium is reached.

Charges and Direction

  • Conventional Current: Defined as the direction a positive test charge would move, which is opposite to the true flow of electrons (negative charges).

Producing Electric Current

  • To maintain electric potential difference, charged particles are pumped from the lower potential back to the higher potential.

  • This requires an external energy source (e.g., batteries convert chemical energy or photovoltaic cells convert light energy into electric energy).

Electric Circuits

Definition of an Electric Circuit

  • Closed loop or conducting path that allows electric charges to flow.

  • Components of a Circuit: Includes a charge pump to increase potential energy and devices that utilize or reduce that energy, converting it into other forms of energy (light, heat, etc.).

Charge Conservation

  • Charge is conserved in a circuit; charges cannot be created or destroyed but can be separated.

  • The total charge remains constant throughout the circuit.

Energy Conservation

  • The change in electric energy is given by (\Delta E = q \Delta V) (q = charge, (\Delta V) = potential difference).

  • The net change in potential energy around a complete circuit must equal zero.

Rates of Charge Flow and Energy Transfer

Electric Current Formula

  • Electric current (I) is defined as the rate of flow of charge: (I = \frac{q}{t}), where q is charge and t is time.

  • Unit of Electric Current: The ampere (A), equivalent to one coulomb per second.

Energy and Power in Circuits

  • Energy carried by a current depends on charge transferred and the potential difference: (E = q \Delta V).

  • Power delivered to a device is calculated using (P = \frac{E}{t}), substituting energy and charge flow gives (P = I \Delta V).

Resistance and Ohm's Law

Resistance Defined

  • Resistance determines how much current flows in a circuit: (R = \frac{\Delta V}{I}).

  • Measured in ohms (Ω); 1Ω allows 1 A to flow with 1 V applied.

Ohm's Law

  • For conductors obeying Ohm's Law, resistance remains constant regardless of potential difference.

  • Most metallic conductors fit this model, while other components like transistors do not.

Resistors

  • Devices designed to maintain a specific resistance, can be made of materials like graphite, semiconductors, or thin wires.

  • A variable resistor (potentiometer) adjusts current within circuits.

Circuit Diagrams

Representing Circuits

  • Circuits can be described verbally, through photographs, or in schematic form.

  • Common circuit symbols are important for effective representation.

Parallel and Series Connections

Parallel Connections

  • In a parallel connection, components align alongside each other, allowing multiple paths for current flow.

  • The potential difference is equal across all components connected.

Series Connections

  • A series connection allows only one single path for current to flow.

  • Current through a component also travels through the ammeter, enabling measurement of current accurately.

Essential Vocabulary

  • Electric Potential Difference: The difference in electric potential energy per unit charge.

  • Conventional Current: Assumed flow of positive charge.

  • Ampere (A): Unit of electric current.

  • Resistance (R): Measure of opposition to current flow.

  • Series Connection: A single path for current flow.

  • Parallel Connection: Multiple paths available for current flow.