Electricity In The Home Science Notes JC-Learn JC-Learn

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Electricity In the Homeand ElectronicsScience NotesJC-LearnScience NotesElectricity in the Home andElectronics1 PageJC-Learn

Electricity In the Homeand ElectronicsScience NotesJC-LearnElectricity in the Home andElectronicsMains supply and safetyThe mains supply to the sockets in your house or school is at 230 Va.c. This voltage could push a big enough current through your bodyto kill you. There are two cables from mains supply to your home orschool. One is called the live. The other is the neutral.The Set-up1. The main fuse is on live wire as it comes into homes2. Then, both wires pass through electricity meter, which recordsnumber of units used.3. Both wires then pass to distribution box/ fuse box.Fuses and circuit breakers are safety components in electric circuits.Both cut off current in circuit if current becomes too big. Fuses workusing heating effect of electric current. Circuit breakers use themagnetic effect of an electric current. Fuses of various ratings are available (1 A, 3 A etc.). A fuse, forexample, will melt if a current of more than 5 A flows throughit. When a fuse melts like this, it cannot be used again. Circuit breakers simply ‘trip’ off if the current goes above acertain value. The switch needs only to be closed again whenthe fault in the circuit has been corrected. The circuit breakerdoes not have to be replaced. A circuit breaker also actsquicker than a fuse.Most appliances are connected to an electricity supply by pushing aplug into a wall socket. Most plugs have three terminals – live (brownin colour), neutral (blue) and earth (green/yellow). The earthterminal is connected to a metal plate buried in the earth. It is therepurely as a safety device to protect the user of an appliance.2 Page

Electricity In the Homeand ElectronicsScience NotesJC-LearnThe cost of electricityPower can be defined as the energy used per unit time. The unit ofpower is the watt. The ESB sell electricity in amounts, which they call‘units’. The normal unit of energy is the joule but is too small forcosting purposes. So, the ESB use the kilowatt-hour (kW h). A kilowatt-hour is the electrical energy converted by a 1 kWappliance running for 1 hour.If a power rating of an appliance is in watts (W), convert it tokilowatts (kW h) by dividing by 1000. Number of kilowatt-hours (or ‘units’) used number ofkilowatts number of hours Cost (number of kilowatt-hours used) (price per kilowatthour)ElectronicsThe key to most of the development in electronics was the microchip.Each circuit may have several electrical components or parts withvarious functions. Some of the components include the diode, theLED and the LDR.1. The Diode – a diode is a device that allows current to pass throughit in one direction only. One end of the diode is the cathode (-) andthe other end is the anode ( ).3 Page

Electricity In the Homeand ElectronicsScience NotesJC-Learn If the cathode is connected to the negative terminal of thebattery and the anode is connected to the positive terminal, thediode will conduct a current and is forward biased. If the cathode is connected to the positive of the battery andthe anode is connected to the negative terminal, then the diodeis reverse biased and will not conduct a current. Uses of a diode include a rectifier (changes alternating currentsto direct currents) or to protect appliances that use directcurrent.2. The Light Emitting Diode (LED) – An LED is a special diode, whichgives out light when current passes through it. A lens at top of LEDhelps to focus the emitted light. The shorter cathode lead is near theflat edge at base of LED. A LED is a diode, so current will only flow through it when it isforward biased.4 Page

Electricity In the Homeand ElectronicsScience NotesJC-Learn A LED requires only a very small current, especially whencompared to an ordinary bulb. Uses of LEDs make useful indicator lamps and many clocks useLEDs as digital displays.3. The Light Dependent Resistor – The LDR is a special type ofvariable resistor. Its resistance varies with the amount of lightshining on it. In dim light, the LDR has high resistance and allows littlecurrent through. In bright light, the resistance of the LDR is low, and it allowsmuch more current through. Uses of LDRs include cameras and burglar alarms.5 Page

Electricity In the Home Science Notes JC-Learn and Electronics 3 P a g e The cost of electricity Power can be defined as the energy used per unit time. The unit of power is the watt. The ESB sell electricity in amounts, which they call ‘units’. The normal unit of e

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