Using Electricity In The Home
Resumen
A torch and a table lamp both light up, and the supplies behind them could hardly be less alike. The torch cell pushes charge around its circuit one way and keeps pushing that way until it is flat. The lamp is fed by a supply that reverses itself a hundred times a second, is powerful enough to kill, and is trusted anyway because three wires, a strip of thin metal and a switch that flicks itself off stand between it and the person holding the plug.
This lesson is about telling those two supplies apart and about the arrangements that make the dangerous one safe to live with. You will learn to read a supply straight off a screen: how many volts the crest of a wave is worth, how long one cycle lasts, and how to turn that time into a frequency in your head. Then you will follow a single fault through a metal cased appliance, from the loose live wire that makes the case dangerous to the fuse that melts a fraction of a second later, and see why every one of those protective devices belongs in the same one of the wires. Every statement in this topic is set for both tiers, so nothing in it is somebody else's problem.
Objetivos
- Cells and batteries supply current that always passes in the same direction. This is called direct current (dc).
- An alternating current (ac) is one that is repeatedly changing direction. Students should be able to determine the period, and hence the frequency, of a supply from diagrams. They should be able to compare and calculate potential differences of dc supplies and the peak potential differences of ac supplies from diagrams.
- Mains electricity is an ac supply, which has a set frequency and voltage. Knowledge of root mean square (rms) measurements and values are not required.
- There are a number of safety features that can be incorporated in electrical systems and appliances. One of these is earthing: if the metal body of an appliance becomes live through a fault, the current is harmlessly conducted away.
- If an electrical fault causes too great a current to flow, a fuse or a circuit breaker in the live wire disconnects the circuit. The current will cause the fuse wire to overheat and melt or the circuit breaker to switch off (‘trip’). A circuit breaker operates much faster than a fuse and can be reset.
- Appliances with metal cases are usually earthed. If a fault develops a large current flows from the live wire to earth. This melts the fuse and disconnects the live wire. Students should be aware that some appliances are double insulated and therefore have no earth wire connection.
Mapa mental
Este tema esta esquematizado para ver como se conectan las ideas.
Abre el mapa mental en la app
Nota de la lección
Apunte completo disponible en la aplicacion Green Bridge
Instala la aplicacion Green Bridge CBT en tu movil u ordenador para acceder a toda la biblioteca IGCSE: examenes anteriores, criterios de correccion, mapas mentales, tarjetas de estudio y lecciones en audio.
Evaluación de la lección
Felicitaciones por completar la lección del Using Electricity In The Home. Ahora que has explorado el conceptos e ideas clave, es hora de poner a prueba tus conocimientos. Esta sección ofrece una variedad de prácticas Preguntas diseñadas para reforzar su comprensión y ayudarle a evaluar su comprensión del material.
Te encontrarás con una variedad de tipos de preguntas, incluyendo preguntas de opción múltiple, preguntas de respuesta corta y preguntas de ensayo. Cada pregunta está cuidadosamente diseñada para evaluar diferentes aspectos de tu conocimiento y habilidades de pensamiento crítico.
Utiliza esta sección de evaluación como una oportunidad para reforzar tu comprensión del tema e identificar cualquier área en la que puedas necesitar un estudio adicional. No te desanimes por los desafíos que encuentres; en su lugar, míralos como oportunidades para el crecimiento y la mejora.
- Which of these supplies a current that always passes in the same direction? A. A battery B. The mains supply C. A supply set to make a wave at 50 Hz D. A supply whose trace keeps crossing the zero line Answer: A
- One complete cycle of an alternating supply occupies 4 divisions on a screen. The time setting is 5 ms per division. What is the frequency of the supply? A. 20 Hz B. 50 Hz C. 200 Hz D. 250 Hz Answer: B
- In which wire of a mains circuit must a fuse or a circuit breaker be fitted? A. The live wire B. The neutral wire C. The earth wire D. Either the live wire or the neutral wire Answer: A
- Which statement gives an advantage of a circuit breaker over a fuse? A. It is cheaper to make B. It operates much faster and can be reset C. It allows a larger current to flow before acting D. It does not need to be connected to the live wire Answer: B
- Why does a double insulated appliance not need an earth wire connection? A. It is supplied with direct current B. It draws only a very small current C. Its casing does not conduct, so no part the user touches can become live D. Its fuse is fitted in the neutral wire instead Answer: C
Resuelve estas preguntas en la aplicacion
Resuelve estas preguntas en la aplicacion
Libros Recomendados
Practica preguntas simuladas
¿Quieres practicar preguntas simuladas sobre Using Electricity In The Home? Descarga la aplicación Green Bridge CBT para acceder a preguntas simuladas y evaluaciones completas sobre este tema.
Descarga la aplicación en Google Playstore.
Todo lo que necesitas para destacar en JAMB, WAEC y NECO.
