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Pratical electricity

1) The document discusses the safe use of electricity in the home. It describes common electrical appliances like lighting, heating, and motors. 2) It outlines electrical hazards such as damaged insulation, overheating of cables, damp conditions, and carelessness that can cause electric shock. 3) The document provides guidance on safely using electricity through the use of fuses, circuit breakers, earthing of appliances, and double insulation to protect against electric shock.

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PRACTICAL ELECTRICITY Uses of electricity Dangers of electricity Safe use of electricity at home
Introduction  Electricity is widely used in the modern world.  In this section, we will be looking at some common household appliances that use electricity , the major hazards and safe use of electricity.
Uses of Electricity  Electricity is most commonly used in electric heating, lighting and motors.
Electrical lighting  When the switch is closed, current flows through one wire to the lamp, lights it up, and flows back through the other wire. This completes the circuit.
Electrical heating  When the switch at the socket is on, current flows through one wire in the cable to the kettle. The current goes into the kettle and heats up the water. The current then leaves, goes through a different wire in the cable, and return to the other contact point on mains socket.
Electrical Motors  A motor is used in the electric fan. The electric fan normally has a cable that plugs into the mains socket on the wall. When the switch on the mains socket is on, current flows through one wire in the cable, and goes into the motor in the fan. The motor then rotates the fan.
Electrical calculation  POWER Electrical power of an appliance is given by the formula power = current × voltage, unit of power= watt(W) VIP
Electrical calculation  ENERGY Electrical Energy of an appliance is given by the formula energy = power x time = current x voltage x time unit of energy: Joule (J) tVIE
Electrical cost calculation Our daily household energy consumption is not a free service, that is we have to pay a monthly bill for the electricity we used in our houses. In order to calculate the cost of this energy consumption, we have to sum all the energy we used and then multiply it to the value for each unit of electrical energy we use. The total amount of energy consumed is recorded in the electricity meter found in all household that has electricity. Note: The energy consumption is recorded in kilowatt-hour (KWh) CALCULATION of energy consumption: Energy(E) = Power (P) x Time(t) (kWh) (kW) (h) CALCULATION of cost: Cost = Energy(E) x cost of 1KWh (Rs/$) (KWh) (Rs/$)
Exercises 1. A light bulb is connected to a 240 V supply. The current that flows through it is 0.1 A. What is the rate at which light and heat is emitted by the light bulb? 2. The sticker on a compact disc player says that it draws 288 mA of current when powered by a 9 Volt battery. What is the power (in Watts) of the CD player? Calculate the energy used if it is put on for 2h? 3. A color TV has a current of 1.99 Amps when connected to a 120-Volt household circuit. What is the resistance (in ohms) of the TV set and calculate its power? 4. A hairdryer has a power-rating of 750W. If a unit of electricity costs rs21, how much does it cost to run the appliance for a year if it is switched on for 10 minutes each day? 5. A cooker has a power-rating of 3kW. If a unit of electricity costs rs17, how much does it cost to run the appliance for 3 hours?
Hazards of electricity Damaged insulation Overheating of electrical cables Hazards in damp conditions direct contact(carelessness)
Hazards of electricity  Damaged Insulation The wires in each cable are insulated from one another, and the whole cable has more protective insulation around the outside. If this insulation is damaged, there is a chance that the user will touch the bare wire and get an electric shock. There is also a chance that current will flow between two bare wires, or from one bare wire and any piece of metal it comes in to contact with.  Overheating of cables Some times another hazard can arise if an excessive current flows in the wires. They will heat up and the insulation may melt, causing it to emit poisonous fumes or even catch fire. Thus it is vital avoid using appliances that draw too much current from the supply.
Hazards of electricity  Damp conditions When using electricity, it is important to avoid damp or wet conditions. Because water is an electrical conductor. So if your hands are wet when you touch an electrical appliance, the water may provide a conductive path for current to flow from a live wire through you to earth. That could prove fatal.  Carelessness sometimes, people tend to be very careless when handling electrical cables and appliances. As metal appliances which are not earthed are great dangers to people. Low electrical sockets can be hazardous to small children as they may take metal objects and play with these sockets thus endangering themselves.
Safe use of electricity  Fuses Fuses are included in circuits to stop excessive currents from flowing. if the current gets too high, cables can burn out and fire can start. A fuse contains a thin section of wire, designed to melt and break if the current gets above a certain valueuses It is important to choose a fuse of the correct value in order to protect an appliance. The current rating of the fuse should be just above the value of the current that flows when the appliance is operating normally. Maximum current allowed = 3 A Fuses rating = 3.1-3.5A THE FUSE IS A DEVICE USED TO PROTECT EQUIPMENT AND WIRING FROM EXCESSIVE CURRENT FLOW.
Safe use of electricity  Circuit breaker A circuit breaker is an automatic switch which cuts off the current in a circuit if this rises above a specified value. It has the same effect as a fuse but, unlike a fuse, can be reset (turned ON again) after it has tripped (turned OFF). When the live wire carries the usual operating current, the electromagnet is not strong enough to separate the contacts. If something goes wrong with the appliance and a large current flows, the electromagnet will pull hard enough to separate the contacts and break the circuit. The spring then keeps the contacts apart. After the fault is repaired, the contacts can be pushed back together by lifting a switch on the outside of the circuit breaker.
Safe use of electricity  Earthing Sometimes, even the fuse cannot capture the high currents coming from the live wire into the household appliance, earthing further protects the user of the appliance from electric shock by connecting the metal casing of the appliance to earth (a wired connection to the bare ground). In the event that the metal casing of the appliance becomes live, earthing diverts large currents into the earth by providing an alternate path to the large current flow via the earth wire, rather than through the user’s body.
Safe use of electricity  Double Insulation Alternatively, instead of earthing, appliance can be made with double insulation. Double insulation protects the user of the appliance from an electrical shock by preventing any possibility of the external casing becoming live, thus eliminating the need for an earth connection. First insulation: Insulating electrical cable from the internal component of the appliance. Second insulation: Insulating internal metal part which could become live from the external casing. Symbol of double insulation
Live, Neutral and Earth wires  Live wire carries electric current to the appliances.  Neutral wire completes the circuit by forming a path for the current back to the mains. It is usually at zero volts.  Earth wire has very low resistance and is usually connected to the metal casing of the appliances. It forms a safety outlet for current in case the appliance becomes live.
How to wire a mains plug?  The LIVE wire is BROWN. This is connected to a fuse on the live pin. The electric current uses the live wire as its route in.  The NEUTRAL wire is BLUE. This is the route the electric current takes when it exits an appliance; it is for this reason the neutral wire has a voltage close to zero.  The EARTH wire is GREEN & YELLOW and connected to the earth pin. This is used when the appliance has a metal casing to take any current away if the live wire comes in contact with the casing.
Why should fuses and circuit breakers be connected to live wires?  As mentioned above, live wire is the one that carries current to the appliances. If ever there is a too bog current that is being carried to the appliance, then it may get damaged.  In order to avoid this problem, a fuse or a circuit breaker should be connected to the live wire, that will cause the circuit to break if ever the current is too large.