Circuit Basics and Electrical Concepts

Definition: Components in a series circuit are connected along a single, continuous path.
Current Flow: The same electrical current flows through all components within the circuit.
Component Removal Consequence:
- If any component is removed from a series circuit, the electrical current can no longer flow.
- The circuit becomes "open," effectively deactivating all other components.
Example: A series circuit containing three indicator lights (1, 2, and 3).
- The source current ( $I_s$ ) flows through all three lights.
- Removing indicator light 3 prevents current flow to the entire circuit, thus turning off indicator lights 1 and 2 as well.

Electricity: Fundamentally, electricity is defined as the flow of electrons through a conductor.
Requirement for Flow: For electrons to flow, a force must act upon them.
Nomenclature: This force is known as electromotive force (EMF) or, more commonly, voltage.
Intensity of Force: The voltage across a conductor quantifies the intensity of this driving force.
- A higher voltage indicates a greater force compelling electrons to flow.
Measurement Unit: Voltage is measured in volts ( $V$ ).
- The unit is named after the Italian physicist Alessandro Volta, who invented the first chemical battery.
Symbolic Representation: In this course, voltage is denoted by $E$ . It is also frequently represented by $V$ or $U$ in other contexts.

Simultaneous Control: When a toggle switch is placed in a series circuit, it controls all components within that circuit simultaneously.
Example: A series circuit featuring an indicator light and a buzzer.
- Open Switch: If the toggle switch is open, no current flows, and consequently, both the indicator light and the buzzer remain off.
- Closed Switch: Conversely, when the toggle switch is closed, current flows, activating both the indicator light and the buzzer.
Limitation: A critical implication of this configuration is that independent control of different components within a series circuit is impossible.

Illustrative Purpose: This analogy helps to visualize the relationship between voltage and current.
Analogy Setup: Consider a water tank with a discharge tube at its base, where gravity causes water to flow out.
Key Relationships in Water System:
- Water Quantity: The amount of water in the tank directly corresponds to the water pressure.
- Water Pressure: A higher quantity of water leads to higher pressure at the outlet.
- Water Flow: Greater pressure at the outlet results in a larger flow of water.
Electrical Parallel:
- Voltage as Pressure: Higher voltage creates greater "pressure" on the electrons.
- Current as Flow: This increased pressure drives a larger flow of electrical current.
Visual Representation:
- (a) Filled water tank: Represents high voltage, characterized by high water pressure and resulting in high water flow.
- (b) Depleted water tank: Represents low voltage, characterized by low water pressure and resulting in low water flow.

There are two primary conventions for representing current direction in a circuit:

Electron Flow Direction:
- Description: This method depicts current flowing from the negative terminal to the positive terminal of a power source.
- Basis: It follows the actual physical movement of electrons.
- Usage: Illustrated by a red arrow (as in diagram (a)), this method is rarely used in practical applications and will not be followed in this course.
Conventional Current Direction:
- Description: This method depicts current flowing from the positive terminal to the negative terminal of a power source.
- Basis: It is based on the historical assumption that current is carried by positive charges, even though electrons are the actual charge carriers.
- Usage: Shown by a blue arrow (as in diagram (b)), this is the standard representation and will be used throughout this course.