Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Electric current
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Electric current
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Subject: Basic Electronics
Class: Senior Secondary 1
Term: 1st Term
Week: 5
Theme: Electrical Quantities
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Explain the structure of at om. Define conductors and in sulators State uses of conductors and in sulators. Distinguish between direct and alternating current. Explain the sources of direct and alternating current.
All matter, including the materials used in electronics, is composed of tiny particles called atoms. An atom is the smallest unit of an element that retains the chemical properties of that element.
Components of an Atom: An atom consists of a central nucleus and electrons orbiting this nucleus.
Nucleus: The dense, central part of an atom. It contains two types of subatomic particles: Protons: Positively charged particles. The number of protons determines the atomic number of an element.
Neutrons: Electrically neutral particles (no charge). Neutrons add mass to the atom. The nucleus, therefore, carries a net positive charge.
Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells, much like planets orbiting the sun. Electrons are much lighter than protons and neutrons. In a neutral atom, the number of electrons is equal to the number of protons, making the atom electrically neutral overall.
Electron Shells and Valence Electrons: Electrons occupy distinct energy levels or "shells" around the nucleus. Each shell can hold a specific maximum number of electrons. The outermost shell is called the valence shell, and the electrons in this shell are called valence electrons.
Significance of Valence Electrons: Valence electrons are crucial for understanding electrical conductivity. They are the electrons involved in chemical bonding and, more importantly for electronics, in the flow of electric current. Materials with very few valence electrons (typically 1-3) that are loosely bound to the nucleus can easily lose these electrons. These are called free electrons and are responsible for electrical conductivity. Materials with many tightly bound valence electrons (typically 5-8) do not easily release them. The ability of a material to allow electric current to flow through it depends on its atomic structure, specifically the availability of free electrons.
Conductors: Definition: Conductors are materials that allow electric current (the flow of electric charge) to pass through them easily.
Explanation: They have a large number of free electrons in their outermost shells that are loosely bound to the nucleus. These free electrons can move easily from one atom to another under the influence of an electric field, creating an electric current.
Properties: Offer very low resistance to the flow of electricity.
Examples relevant to Nigeria: Metals: Copper (most common for electrical wiring in homes, offices, and power cables in Nigeria due to its excellent conductivity and relative affordability), Aluminium (used for overhead power transmission lines, e.g., PHCN/DISCOs, due to its lighter weight and lower cost than copper, though less conductive), Silver (best conductor but too expensive for general use), Gold (used in high-quality connectors due to corrosion resistance).
Water (impure/tap water): Tap water in Nigeria often contains dissolved minerals and salts, which provide ions (charged particles) that can conduct electricity. Pure water (distilled water) is a poor conductor.
Human Body: Contains fluids with dissolved salts, making it a good conductor and susceptible to electric shock.
Uses in Nigeria: Electrical wiring (copper cables from mains to appliances), overhead transmission lines (aluminium), electronic circuit boards, heating elements (e.g., in electric kettles, pressing irons).
Insulators: Definition: Insulators are materials that strongly resist the flow of electric current.
Explanation: They have very few or no free electrons. Their valence electrons are tightly bound to the atomic nucleus and require a very strong external force to be dislodged.
Properties: Offer very high resistance to the flow of electricity.
Examples relevant to Nigeria: Plastics: PVC (Polyvinyl Chloride) and rubber are commonly used as outer sheathing for electrical cables and wires (e.g., Legrand switches, electrical tape).
Glass: Used in some electrical components, older light bulbs, and insulators on power poles (though porcelain is more common now).
Wood (dry): Dry wood is a fair insulator; however, wet wood can conduct electricity.
Air: A good insulator under normal conditions, preventing sparks from jumping large distances.
Porcelain/Ceramic: Widely used as insulators on power transmission poles and for electrical fittings (e.g., fuse holders, lamp holders).
Mica: Used in high-temperature applications due to its excellent insulating properties (e.g., in pressing irons, toasters).
Uses in Nigeria: Cable sheathing, electrical switches and sockets, fuse casings, insulation on power lines, handles of electrical tools (screwdrivers, pliers), protective gloves for electricians. Electric current can be classified into two main types based on its direction of flow.
Direct Current (DC): Definition: Direct Current is an electric current that flows in only one direction through a circuit. The magnitude of the current can be constant or vary over time, but its direction remains unchanged.
Explanation: Electrons flow from the negative terminal to the positive terminal of the power source in a continuous, unidirectional path.
Waveform: Often represented as a straight line on a voltage-time graph, indicating constant voltage and current, or a pulsating line if unfiltered (e.g., from a rectifier).
Sources of DC in Nigeria: Batteries: Dry cells (e.g., AA, AAA batteries for remote controls, flashlights), car batteries (12V, for vehicle electrical systems), rechargeable batteries (for mobile phones, laptops, power banks).
Solar Panels (Photovoltaic cells): Directly convert sunlight into DC electricity, increasingly popular in Nigeria for homes and businesses.
DC Generators (Dynamos): Produce DC, often found in older vehicles or specific industrial applications.
Rectified AC: AC is converted to DC using electronic circuits called rectifiers (e.g., in phone chargers, computer power supplies).
Uses in Nigeria: Powering portable electronic devices (phones, laptops, radios), automobiles, LED lights, charging systems, solar home systems.
Alternating Current (AC): Definition: Alternating Current is an electric current that periodically reverses its direction of flow. It also continuously changes its magnitude with time, typically in a sinusoidal pattern.
Explanation: Electrons do not flow continuously in one direction but oscillate back and forth within the conductor. The voltage and current rise to a maximum in one direction, fall to zero, then rise to a maximum in the opposite direction, and fall back to zero, completing a cycle.
Frequency: In Nigeria, the standard frequency for AC is 50 Hertz (Hz), meaning the current reverses direction 50 times per second.
Waveform: Typically represented as a sine wave on a voltage-time graph.
Sources of AC in Nigeria: AC Generators (Alternators): Large-scale power generation in power plants (hydro, thermal, gas plants that supply the national grid managed by the Transmission Company of Nigeria (TCN) and distributed by DISCOs).
Mains Electricity (National Grid): The primary source of electricity supplied to homes, offices, and industries throughout Nigeria (e.g., PHCN/DISCOs supply).
Inverters: Convert DC from batteries (e.g., solar battery banks) into AC to power household appliances when mains electricity is unavailable.
Portable Generators: Commonly used in Nigeria to provide supplementary power during outages.
Uses in Nigeria: Powering homes and industries (lights, refrigerators, air conditioners, fans, industrial machinery), long-distance power transmission (more efficient than DC for long distances), induction cooking. | Feature | Direct Current (DC) | Alternating Current (AC) | | :------------------ | :-------------------------------------------------- | :--------------------------------------------------------- | | Direction of Flow | Flows in one constant direction. | Periodically reverses its direction of flow. | | Magnitude | Usually constant (steady voltage/current). Can be pulsating. | Continuously changes in magnitude from zero to maximum in one direction, then to zero, then to maximum in the opposite direction. | | Polarity | Has definite positive (+) and negative (-) terminals. | Polarity reverses periodically; no fixed positive/negative terminals in an AC circuit. | | Sources | Batteries, solar cells, DC generators, rectified AC. | AC generators (alternators), mains electricity (National Grid/DISCOs), inverters, portable generators. | | Transmission | Difficult to transmit efficiently over long distances due to voltage drop. | Can be transmitted efficiently over long distances using transformers to step up/down voltage. | | Frequency | Zero frequency (0 Hz). | Has a specific frequency (e.g., 50 Hz in Nigeria). | | Applications | Portable electronics, charging, automotive systems, LED lighting, electronic circuits. | Homes, offices, industrial power, large motors, heating appliances, national power grids. |
This topic has profound relevance to the daily lives of Nigerians and integrates with several aspects of their community, environment, and economy.
Electrical Safety and Infrastructure: Application: Understanding conductors and insulators is critical for electrical safety in homes and workplaces. The rubber or plastic insulation around electrical wires (e.g., those from the national grid or generators) prevents short circuits and electric shocks. Electricians use tools with insulated handles (e.g., rubber-coated pliers, screwdrivers) to protect themselves while working on live circuits.
Integration: Students learn to appreciate the design of Nigeria's electrical infrastructure, from the high-tension lines (aluminium conductors, porcelain insulators) that transmit power across states (e.g., from Egbin Power Plant to Lagos) to the copper wiring within their homes. This knowledge informs responsible usage and maintenance of electrical systems, reducing accidents prevalent in areas with informal electrical connections. Powering Homes and Businesses (AC vs.
DC): Application: Nigerians constantly interact with both AC and DC. The mains electricity supplied by DISCOs (e.g., Eko Electricity Distribution Company, Abuja Electricity Distribution Company) to power homes, schools, and offices is AC, enabling the operation of heavy appliances like refrigerators, air conditioners, and industrial machinery. Conversely, portable devices like mobile phones, laptops, and torchlights rely on DC from batteries or solar panels.
Integration: This distinction is crucial for understanding the widespread use of generators and inverters in Nigeria due to inconsistent grid supply. Generators produce AC, while solar panels produce DC, which often needs to be converted to AC by an inverter to power standard household appliances. Students can appreciate the energy choices made by families and businesses for reliability and efficiency.
Renewable Energy and Sustainability: Application: The knowledge of DC is foundational for understanding solar power systems, which are increasingly adopted in Nigeria as a sustainable energy alternative. Solar panels directly generate DC, which can be stored in batteries (DC) and then, if needed, converted to AC by an inverter for domestic use.
Integration: This connects the topic to environmental awareness and economic sustainability. Students can explore how communities in remote, off-grid areas of Nigeria leverage DC-generating solar technology to power essential services like lighting, water pumps, and small businesses, reducing reliance on fossil fuels and promoting energy independence.