Domestic electric circuit

Q. 1     Name the types of wires or cables provided by state electricity board for houses & factories in electric power supply.

Ans.    The wires or cables used in the electric power supply provided by state Electricity Board are of three types 
         (i) Phase wire (or live wire which carries electric current)

         (ii) Neutral wire (iii) The earth wire.

Q. 2     In a domestic electric supply in India, what is the potential difference between the live wire & the neutral wire.

Ans.   In a domestic electric supply in India, the potential difference between the live wire & the neutral wire is 220V-250V.

Q. 3     Name the type of wire to which the main fuse is connected.

Ans.     The main fuse is connected to the live wire (phase wire).

Q. 4     What does the electricity meter measures ?

Ans.   The electricity meter measures electric energy consumption. It is expressed in ‘Units’, where 1 unit means 1 kilowatt hour (= 3.6 x 10⁶ Joules)

Q. 5     Name the types of wires across which an electric appliance is connected.

Ans.     An electric appliance is connected across the live wire (phase wire) & the neutral wire.

Q. 6     Write short notes :

I.          Earthing OR What is Earthing? Explain its importance.

Ans.     The system of connecting the metal casing of an electrical appliance to a copper plate. Buried   deep inside the earth is called earthing.

           Many appliances such as electric heater, a toaster, an oven, a refrigerator etc. have a metallic body (casing). If by chance the insulation of the wire or the cable melts, the live wire may touch the metal casing. In case, if we touch the casing carrying a current, we may receive a severe shock which may cause death. To avoid this metal casing of all electrical appliances are earthed. One end of a thick copper wire is connected to the metal casing of the appliance & the other end is connected to a copper plate buried deep inside the earth. The current through the metal caring then flows to the earth & the person touching the casing is saved.

II.        Safety measures in using electricity.

Ans. i) Electric switchboards, sockets & appliances should not be within the reach of very small children.

ii)     Never unplug by pulling the cord or the wire connected to the plug. Always pull it by properly holding the plug.

iii)    Before cleaning electric devices such as refrigerators, fluorescent tubes, bulbs, etc. switch off the current & unplug the plugs of the devices so that there is no chance of getting electric shocks.

iv)    Use only dry hands to switch on or switch off electrical devices.

v)    Never open an electrical or electronic device when you do not know how it works.

vi)   Never play with electricity or electronic devices. This can prove to be dangerous.

vii)  Replace all defective wires & devices.

viii)  Use fuse wires of the appropriate rating.

ix)   Electrical appliances must be switched off when there is lightning, to prevent a fire.

x)    Electrical appliances must be properly earthed.

xi)   Many electrical appliances of high power rating should not be connected in the same circuit.

III.       Short circuiting.

i)      Often the insulation of wires gets worn out & it gets removed.

ii)    When this happens, there are chances of the live wire & the neutral wire coming very close to each other or touching each other.

iii)    When this happen known as short circuiting.

vi)   During a short circuit, the resistance in the circuit becomes very small & a large current flows through it.

v)     This produces a large amount of heat & a very high temperature.

vi)   This causing a fire in the circuit. This fire may spread very fast & engulf even a whole building.

IV.       Overloading Or What is overloading ? When does it occur ?

            What does it cause ? How can overloading be avoided ?

Ans. i) A flow of large amount of current in a circuit, beyond the permissible value of current, is called overloading.

ii)     It occurs when many electrical appliances of high power rating, such as geyser, a heater, an oven, a motor, etc. are switched on simultaneously. This causes fire.

iii)     Over loading can be avoided by not connecting many electrical appliances of high power rating in the same circuit.

Q.7      Give scientific reasons.

«1.     Wires carrying electricity should not be touched when base-footed.

Ans. i) Our body contains different fluids which contains various ions. The cells in our body also contain many ions.

ii)         Therefore, our body is a good conductor of electricity.

iii)        When we are bare- footed, our body is directly in contact with the earth.

iv)        When we touch wires carrying electricity, we may come in contact with a live wire. The current passes through our body to the earth & we get a nasty shock. Hence we should wear shoes with rubber soles (insulator) & not handle wires barefooted.

«2.     We must not use many electrical appliances simultaneously.

 Ans. i) Many of the electrical appliances that we use at home have a high rating e.g. geyser, oven, grinder etc.

ii)         When many such appliances are switched on simultaneously, a large amount of current flows through the main circuit & the current may exceed the permissible amount.

iii)        This causes overloading, which may cause a fire.

iv)        This can be avoided by not using many appliances simultaneously.

3.         Most electrical appliances require earthing.

Ans. i) Many of the electrical appliances such as electric iron, toaster, oven, mixture, geyser, etc. have metal bodies which may come into contact with our body.

ii)         Due to damaged insulation or a defect in the appliances the live wire may come in contact with the metal body, or due to some other problems, some current may leak to the metal body.

iii)        In such cases, the person making a contact with the metal body of the appliance may get an electric shock as our body is a fairly good conductor of electric current.

iv)        If the appliance is properly earthed, there is no danger of an electrical shock as the earthing wire conducts the leakage current to the earth & then the current passing through the person’s body is extremely small. Hence most electrical appliances need earthing.

4.         Water must not be used to extinguish fire caused by short circuit.

Ans. i) Generally, water contains a number of salts & other impurities & therefore, it conducts electricity.

ii)         Hence, if water is used to extinguish the fire caused by a short circuit, electricity is conducted through it & the fire spread. Therefore water must not be used to extinguish fire caused by a short circuit.

5. Electric circuit should be switched off when there is lightning.

Ans. i) When there is a lightning, the cloud is at a very high potential & the earth is at zero potential.

ii)         Due to the low resistance, a very high current passes between the cloud & the earth.

iii)        This causes an enormous amount of heat & a very high temperature.

iv)        Due to this high temperature, the wires in the appliances can get burnt & the appliances can catch fire. This can be avoided by not switching on electrical appliances where there is lightning.

6.         Household wiring must be inspected periodically, & replaced, if found to be defective.

Ans. i) Due to the exposure of insulated wires to heat, light, chemical fumes, variation in temperature, etc. the insulation gets damaged over a long period of time.

ii)         Sometimes rats, mice, cockroaches & fungal growth may damage the insulations.

iii)        Damaged insulation, exposed or bare parts of the wires, can cause short circuits, fire & give electric shocks. Electric consumption can also increase due to leakage of current.

iv)        By inspecting the insulation of all the wires once a year & replacing the damaged ones, is the best way to maintain electrical safety in the house.

7.         In rainy season, we should not touch a wall of a building.

Ans. i) If a bare wire (live wire) comes in contact with a wet wall, an electric current begins to flow through the wall.

ii)         A person touching such a wall gets a severe shock. Hence, in rainy season, we should not touch a wall of a building.

magnetic field due to the coil,magnetic lines of flux current carrying conductor,factor on which tge strength of a magnetic field at a point due to ,current carrying cunductor depends,state 4 magnetic lines of force, magnetic field, magnetic current, the factors on which the magnetic field due to the current carrying in the circular loop depends, magnetic coil, current conductor, Right hand thumb rule, Left hand thumb rule, solenoid, magnetic lines of force, magnetic field lines, due to a current carrying solenoid,  Bar magnet, Electromagnet, magnets  domestic electric supply, types of wires, fuse, main fuse , Earthing, Short circuiting, Overloading, Wires carrying electricity, wiring