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The fuse is placed in the live wire just after the ‘electricity meter’ of the consumer. Fuse wires are generally made of an alloy of tin and lead and have a relatively low melting point.

The three main characteristics of an heating element are: 

(i) It should have a high resistance so that a major amount of electric energy is converted into heat energy. 

(ii) It should not get oxidised easily up to a temperature of 1000°C. 

(iii) It should have a high melting point and a low thermal Expansion so that it does not get loosened on getting heated.

Dual switches are double pole type switches. With such switches an appliance, e.g., and electric bulb can be switched off or on from two different places. They are generally used in staircases, long corridors etc.

 (i) They are used in light houses. 

(ii) They are used in search lights and cinema projection appliances. 

(iii) They are used in electric furnace and electric welding. 

Nichrome and manganin are the common alloys that are mostly used for making heating elements. 

Nichrome is: 60% nickel + 25% iron + 15% chromium. 

Manganin is: 83% manganese + 13% copper + 4% nickel.

The concave reflector, reflects the heat radiations in the forward direction. Thus, large amount of heat radiations are available in one particular direction.

In this position, when current passes through the nichrome wire, it becomes red hot and the concave reflector helps in spreading the heat radiation in the room because it forms a divergent beam on account of the heating element being placed between the pole and the principal focus of the reflector. 

In an electric oven, the china clay plate is provided either with lateral grooves or grooves in the form of a spiral helix. This type of spiral winding reduces the area of spread of nichrome wire and helps to concentrate heat in a small region.

This reduces the area over which element of the heater is spread. As heat is produced over smaller area, therefore temperature of its element rises to about 1000°C.

This reduces the area over which element of heater is spread. As heat is produced over smaller area, therefore temperature of its element rises to about 1000°C.

The metallic wire gets heated up on passing an electric current through it due to collisions of free electrons and energy is transferred to the positive ions which begin to vibrate more violently, causing to produce heat. It is possible to melt the wire by passing a heavy current. The wire will melt when its temperature due to heating reaches its melting point.

From the relation   

Q = vit joule

Applying ohm's law, V = iR

or i = V/R

Substituting the value of i, we get

Q = V.(V/R)t = V²t/Rjoule.

When an electric current passes through a metallic wire, the wire becomes hot and the whole of electric energy is converted into heat energy.

(i) The heat produced is proportional to the square of current passed in the wire. 

(ii) The heat produced is proportional to the resistance of the wire. 

(iii) The heat produced is proportional to the time of passage of current in the wire.

The split ring atts as a commutator in a d.c. motor. With the split ring, the direction of current through the coil is reversed after every half rotation of coil and thus the direction of couple rotating the coil remains unchanged and the coil continues to rotate in the same direction.

The electric power from the generating station is transmitted at high voltage to minimise the loss of energy in the live wires.

At the generating station the electric power is generated at 11,000 volt. This voltage is alternating of frequency 50Hz. To transmit this power to our house the alternating voltage generated at the generating station is first stepped up from 11,000V to 1,32,000V. It is then transmitted to the main sub-station through the high-tension line wires, where it is stepped down to 3,300V and then transmitted to the city sub-station. At the city sub-station, the voltage is further stepped down to 220V for supply to the houses through the overhead line wires.

The earth pin being thicker can never enter live or neutral sockets thus a given electric appliance gets connected only in one proper electrical position, where the live wire, neutral and earthings are connected correctly. 

The earth pins being longer, get connected to earth terminal first, thus ensuring that user will not get electric shock, because the current will melt the fuse in case the electrical appliance is short circuited.

If switch is connected in the neutral wire, an electric appliance, e.g., an electric iron will remain connected to the live wire even when the switch is off and so if any one happens to touch the appliances; he of she will get a shock which is sometimes fatal.

A switch is an on-off device for current flowing in a circuit or in an electric appliance. The switch should always be connected in the live wire. Its main function is either to connect or disconnect an electric appliance in an electric circuit.

switch should not be touched with wet hands because the water forms a conducting layer between the live wire of the switch and the hand and so we may get a fatal shock when the current passes from the ‘live’ wire to the hand. 

Current flowing in bulb = i = P/V = 100/230 = 10/23A = 0.435A

This statement means that the bulb is operated at 230 volt and consumes 100 watt of power.

If an electric bulb is rated as 100W – 230V, it means that the bulb is lighted on a 230V supply, it consumes 100W electric power (i.e., 100J of energy per sec.). 

Rating of an electric appliance indicates energy consumed per second or watt when connected to a supply of given voltage.

Thoriated tungsten (tungsten coated with carbon and thorium) is used as an electron emitter. Thoriated tungsten is used since it has a work function of only 2-6eV and it needs to be heated to only 2000K to emit electrons.

Copper. It is good conductor of heat.

Kilowatt hour is a commercial unit of electric energy consumed. It is also called B.O.T. (Board of Trade) unit and is used throughout the world in calculating the amount of electric energy consumed. kWh is defined as the amount of electric energy consumed by an electric appliance of power 1kW for one hour.

 Energy consumed in Is is 100J. 

∴ Energy consumed in hour = 100 × 60 × 60J = 360000J. 

Watt hour is a smaller commercial unit of electric energy, which is spend by an electric appliance of 

1 watt power in 1 hour, i.e. 

1 watt hour = 1 watt × hour = 1 watt × (60 × 60)s = 3600 joule.

The unit kilowatt hour measures the electrical energy. 1kWh is the electrical energy consumed by an electric appliance of power 1kW when it is used for 1 hour.

The three main disadvantages are: 

(i) Longer length of wire is required for wiring different rooms in a house. Since all circuits start from the main distribution board and so it is comparatively more Expensive. 

(ii) If fuse blows off in any part of the building, it disconnects all the appliances in the circuit.

The two main systems of wiring are: (i) the tree system, and (ii) the ring system. Out of these systems, the ring system is better. The reason is that this system of wiring is cheaper because a low rating wire can be used for connection of appliances.

(i) The statement means that the heater should be connected to 220V Supply and that it consumes 550W power.

(ii) Energy consumed in 3hrs = (550 x 3)/1000 = 1.65Kwh = 1.65 x 3600 = 5940KJ.

(iii) The energy consumed in a resistor when the potential difference is 1V and 1A current flows for 1000 hrs.

The arrangement shown in the figure (i) is a series arrangement.The arrangement in figure (ii) is the parallel arrangement. 

We prefer the parallel arrangement. 

The reasons are: 

(i) In series arrangement if one of the bulb is fused, the other bulbs also cease to glow. But in parallel arrangement, if one bulb fuses, the other bulbs continue to glow. 

(ii) In series arrangement, while one bulb glows if the other bulb is switched on, the resistance of the circuit increases and hence the bulbs glow less bright. But in parallel arrangement, each bulb glows at the same voltage, therefore the glow of a bulb is unaffected if another bulb is switched on. 

In set A, the bulbs are joined in series so there is only one path of current for each bulb. But in set B, the bulbs are joined in parallel so there is separate path of current for each bulb.

No. The wire used in set B must be thicker and of better insulation than that used in set A. The reason is that in set B, the appliances will draw heavy current (= 15A) when they are used, whereas in set A, the appliances will draw ordinary current (= 5A) when they are in use. Therefore, the resistance of wire used in set B must be less than that of wire used in set A. A thick wire has less resistance than a thin wire.

The reason can be that the metallic case of the electric hot plate is not earthed and the live wire of hot plate have come in contact with its case.

Local earthing provides us safety from electric shocking in the case of short circuiting. When excessive current flows through the live wire, it will pass to the earth through the earth wire. In the absence of local earthing, it may causes fire due to over heating of the live wire. 

In the case of an electronic appliance, if its outer metallic body is earthed and by chance, if it happens to touch live wire, then metallic casing acquires the potential of the live wire and so any person touching it is likely to get a total shock. But if earthed, a heavy current flows and the fuse connected to the appliances blows off. Thus the person touching it does not get any shock.

 Earthing of an electrical appliance meant the outer metallic case of appliance is connected with earth, wire which is welded to the end of a copper rod and it is burned in the ground. It save the appliance during short circuiting by passing Excessive current to earth.

(i) The inert gas is filled at very low pressure to prevent oxidation as well as evaporation and thus increases its life. 

(ii) While bulb is working, a convection current is set-up within it which carries the spurting particles of tungsten upward towards the cap and hence the blackening of the lower part (transparent portion) of the bulb is avoided.

The appliances, connected to the light circuit, are supposed to draw currents of the order of 10A to 5A. 

Neutral wire and Earth wire are at same potential and the switch be connected to live wire. 

20A wire is thick as it carries large current and so its area of cross-section will be large.

The current flowing through geyser

= (3 x 1000)/220 = 13.63A = 14A.

The rating of fuse should be just matching with the maximum current carried by the circuit. So the fuse rating should be of 15A.