Basic Electric Circuits, Conductors & Insulators

An electric circuit is a continuous, unbroken conducting pathway along which electric charges (electrons) can flow from the negative terminal of a power source to the positive terminal. • Essential Circuit Conditions: - There must be a source of electromotive force (cell or battery). - The circuit must be a CLOSED, unbroken loop. If there is a break or switch is open, it is an OPEN circuit and no current flows. • Standard Circuit Symbols (BECE Drawing Requirements): - Dry Cell: Two parallel vertical lines—one long thin line (+ positive) and one short thick line (- negative). - Battery: Two or more cells connected in series. - Switch (Key): Open switch (circuit broken) or Closed switch (circuit connected). - Connecting Wire: A straight line drawn with a ruler. - Bulb / Lamp: A circle with a cross (X) inside. - Resistor: A plain rectangle (or zig-zag line). - Ammeter: A circle with letter 'A' inside (measures electric current in Amperes, connected in series). - Voltmeter: A circle with letter 'V' inside (measures potential difference in Volts, connected in parallel). - Fuse: A rectangle with a straight wire passing through its center.

Materials differ in their ability to conduct electric current based on their atomic structure: • Electrical Conductors: - Materials that allow electric current to pass through them freely and easily. - Mechanism: Possess free, delocalized valence electrons that drift easily when a voltage is applied. - Examples: * Metals: Silver (best conductor), Copper (used in domestic electrical wiring), Aluminium (used in overhead high-voltage transmission lines because it is lightweight), Iron, Brass. * Non-Metal Exception: GRAPHITE (a form of carbon with free delocalized electrons, used in battery electrodes and pencil leads). * Liquid Conductors (Electrolytes): Saltwater (aqueous NaCl), dilute acids, molten salts. • Electrical Insulators: - Materials that offer extremely high resistance to the flow of electric current. - Mechanism: Electrons are tightly bound in covalent or ionic bonds with zero free electrons to conduct charge. - Examples: Rubber, Plastics (PVC), Dry wood, Glass, Ceramics, Pure distilled water, Air. - Applications: PVC plastic is coated over copper wires to prevent electric shocks and short circuits; electricians wear thick rubber boots and gloves.

Two primary ways of connecting circuit components: • Series Circuit: - Components are connected end-to-end along a SINGLE, continuous conducting pathway. - Characteristics: * The same electric current flows through all components (I_total = I₁ = I₂). * Total voltage is shared across components (V_total = V₁ + V₂). * If one bulb blows or is removed, the circuit is broken and ALL bulbs go out immediately! * Adding more bulbs increases total resistance, causing all bulbs to become dimmer. • Parallel Circuit: - Components are connected across multiple separate branches. - Characteristics: * Current divides along the different branches (I_total = I₁ + I₂). * Each branch receives the FULL source voltage (V_total = V₁ = V₂). * If one bulb blows or is switched off, the other branches continue working independently! * Adding more bulbs in parallel does not diminish the brightness of the existing bulbs. • Why Homes are Wired in Parallel: 1. Every electrical appliance operates independently with its own dedicated switch. 2. Each appliance receives the full mains supply voltage (230V in Ghana). • Electrical Safety Rules: - Never touch switches or electrical plugs with wet hands (water containing dissolved salts conducts electricity). - Use FUSES or Circuit Breakers: A fuse contains a thin wire with a low melting point that melts ("blows") and cuts off power when excessive current flows, preventing electrical fires. - Earth Wire (Yellow/Green): Safely conducts fault current from metal casings into the ground.