Class 8 ICSE Physics Electricity Notes PDF

Class 8 Physics ICSE | Electricity | Notes Electricity Class-8 Household Electricity Household electricity refers to the electrical power supplied to homes for various domestic purposes, such as...

Class 8 Physics ICSE | Electricity | Notes Electricity Class-8 Household Electricity Household electricity refers to the electrical power supplied to homes for various domestic purposes, such as lighting, heating, cooling, cooking, and powering appliances. It is typically delivered as alternating current (AC) via a distribution network connected to a power grid. Types of Current 1. Direct Current (D.C.) Current remains constant with time E.g. cell or battery 2. Alternating Current (A.C.) Magnitude and polarity changes with time E.g. Mains & Electric generator Sources of Electricity The electric cell and battery The mains (electricity supplied by local electricity board) The generator (or dynamo) The solar cells Class 8 Physics ICSE | Electricity | Notes Electrical Energy and Power Consumed in a Circuit In an electrical circuit, electrical energy is the energy transferred by electric current from a power source to a device. The amount of electrical energy consumed depends on the voltage, current, and the time for which the device operates. It is measured in joules (J) or kilowatt-hours (kWh). Suppose current I is flowing through a resistance R. Colour Coding of Wires Live (or Phase) Wire: This wire carries the current from the power source to the appliance. It is typically red or brown. Neutral Wire: This wire completes the circuit by carrying the current back to the power source. It is usually black or blue. Earth (or Ground) Wire: This wire provides safety by connecting the appliance to the ground, preventing electric shocks. It is green or yellow-green striped. Commercial Unit of Electrical Energy The commercial unit of electrical energy is known as the kilowatt-hour (kWh). It is commonly used by electricity providers to measure and bill consumers for their energy consumption. Class 8 Physics ICSE | Electricity | Notes One kilowatt-hour represents the amount of energy consumed when a device with a power rating of one kilowatt (1 kW) operates for one hour. The energy consumed in kilowatt-hours can be calculated using the formula: Energy (kWh) = Power (kW) × Time (h) For example, if a 100-watt bulb is used for 10 hours, the energy consumed is: Energy = 0.1 kW × 10 h = 1 kWh Electric meter An electric meter, also known as a utility meter or energy meter, is a device used to measure the amount of electrical energy consumed by a household or business. It plays a crucial role in tracking electricity usage for billing purposes. There are mainly two types of electric meters: Analog Meters: Digital Meters: Electric Fuse (A Safety Device) An electric fuse is a safety device used in electrical circuits to protect against excessive current flow, which can cause overheating and potentially lead to fires or damage to appliances. It is an essential component in ensuring electrical safety in homes and industries. Characteristics of a Fuse: Short wire with a low melting point Fuse wire is connected in series with live wire. Thickness of fuse wire depends on its current rating. Class 8 Physics ICSE | Electricity | Notes Miniature Circuit Breaker A Miniature Circuit Breaker (MCB) is an automatic electrical switch designed to protect electrical circuits from overloads and short circuits. Household Electrical Circuits Household electrical circuits are the networks of wires, switches, outlets, and appliances that deliver electricity to various parts of a home. Types of Circuits: Series Circuits: In these circuits, components are connected one after another. If one component fails, the entire circuit stops working. Parallel Circuits: In these circuits, components are connected alongside each other. This allows each device to operate independently; if one device fails, the others continue to work. Hazards of Electricity House circuit overloaded may cause short circuit. Poor insulation can cause short circuit or excess flow of current. Electric shock to a person coming in contact with live wire. Precautions to taken Do not touch switch with wet hands. Connecting wires to the plugs, sockets and switches should be tightly joined. Appliances should be properly earthed. Do not repair appliance while in use. Class 8 Physics ICSE | Electricity | Notes Ensure that MCB or fuse is connected to live wire. Proper insulation of wires. Ordinary copper wire not to be used as fuse wire. Switching off the gadgets by taking out socket from plug. Static Electricity Static electricity refers to the accumulation of electric charge on the surface of objects. Unlike current electricity, which involves the flow of electric charge through conductors, static electricity occurs when there is an imbalance of charges within or on the surface of a material. This can happen due to processes conduction, or induction. Object can be charged by rubbing. Two charged objects having like charges repel each other while two charged objects having unlike charges always attract each other. Kinds of Electric Charges Positive charges Negative charges Like charges repel and unlike charges attract each other. Conservation of Charge Before rubbing, both the objects are uncharged. On rubbing both the objects get equal and opposite charge. Class 8 Physics ICSE | Electricity | Notes Conductors and Insulators Conductors Conductors are materials that allow electric current to flow through them easily. This is due to the presence of free electrons that can move throughout the material. Insulators Insulators are materials that do not allow electric current to flow easily. They have very few free electrons, which restricts the movement of electric charge. Common insulators include rubber, glass, plastic, and wood. Methods of Charging a Conductor Charging a conductor involves creating an imbalance of electric charge on its surface. There are two methods to charge a conductor: by conduction, and by induction. Charging by Conduction In this method, a charged object is brought into contact with a neutral conductor. The excess charge from the charged object spreads over the surface of the conductor, resulting in the conductor becoming charged. Class 8 Physics ICSE | Electricity | Notes Charging by Induction Is a method of transferring electrical energy or charge without direct contact between objects. Electroscope An electroscope is a simple device used to detect the presence and magnitude of electric charge on an object. It is an essential tool in the study of electrostatics and helps demonstrate fundamental concepts of electric charge. Gold leaf electroscope A gold leaf electroscope is an electrostatic device used to detect and measure electric charge. It is a more advanced version of the electroscope and provides a visual indication of the presence and magnitude of electric charge. When a charged object is brought close to the metal rod, it induces a charge in the gold leaves. If the object is positively charged, it attracts electrons from the leaves, making them positively charged. If the object is negatively charged, it repels electrons, resulting in negatively charged leaves. As the gold leaves acquire the same type of charge (either both positive or both negative), they repel each other and spread apart. Class 8 Physics ICSE | Electricity | Notes Lightning Lightning is a powerful and spectacular natural phenomenon that occurs during thunderstorms. It is a sudden electrostatic discharge that creates a bright flash of light and is accompanied by thunder. Safety Measures to be taken: Do not stand under a tree or near a tall building. Rush to a safe place such as low house/building. Sit inside a car/bus and keep windows/doors closed. Do not carry an umbrella. Take out plugs of TV, computer, etc. Do not use wired phone. Lightning Conductor A device which is used to protect buildings from being damaged due to lightning. When lightning strikes a building, the lightning conductor provides a direct path for the electrical charge to travel safely to the ground. This prevents the electrical current from passing through the building's structure, which could cause fires, explosions, or electrical failures.