14and its Effects Electric Current

1 SCIENCE160 Electric Currentand its Effects14 You might have tried the game How steady is your hand? suggested in Chapter 12 ofClass VI. If not, you may try it out and Boojho had also set up thegame by connecting an Electric circuitas suggested in Class VI. They had lotsof fun trying it out with their familiesand friends. They enjoyed it so muchthat they decided to suggest it to acousin of theirs who stayed in adifferent town. So, Paheli made a neatdrawing showing how the variouselectric components were to beconnected ( ).Fig. Setup to check how steadyyour hand isCan you draw this circuitconveniently? It made Boojho wonder ifthere was an easier way to representthese Electric SYMBOLS OF ELECTRICCOMPONENTSSome common Electric components canbe represented by symbols.

2 In Table ,some Electric components and theirsymbols are shown. You may comeacross different symbols for thesecomponents in different books. However,in this book, we shall be using thesymbols shown at the symbols carefully. In thesymbol for the Electric cell, notice thatthere is a longer line and a shorter butthicker parallel line. Do you recall thatan Electric cell has a positive terminaland a negative terminal? In the symbolof the Electric cell, the longer linerepresents the positive terminal and thethicker, shorter line represents thenegative a switch the ON position andthe OFF position are represented by thesymbols as shown. The wires used toconnect the various components in acircuit are represented by Table , a battery and itssymbol are also shown.

3 Do you knowwhat a battery is? Look at the symbol ofa battery. Can you make out what abattery could be? For some of theactivities we may need more than onecell. So, we connect two or more cellstogether as shown in Notice2022-23 Electric Current AND ITS EFFECTS161 Many devices such as torches,transistors, toys, TV remote controls, usebatteries. However, in some of thesedevices the Electric cells are not alwaysplaced one after the other as shown inFig. Sometimes the cells are placedside by side. Then how are the terminalsof the cells connected? Look carefullyinside the battery compartment of anydevice. There is usually a thick wire ora metal strip connecting the positiveterminal of one cell to the negativeterminal of the next cell ( ). Inorder to help you to place the cellscorrectly in the battery compartment, + and symbols are usually can we connect the cells toprepare batteries for our activities?

4 Youmay make a cell holder, as shown , using a wooden block, two ironstrips and rubber bands. It is necessaryFig. Connecting two cells together to makea batteryFig. (a) A battery of two cells(b) A battery of four cells(a)(b)Table Symbols for someelectric circuit in ON in OFF the positive terminal of one cell isconnected to the negative terminal of thenext cell. Such a combination of two ormore cells is called a the rubber bands hold the metalstrips could also buy cell holders fromthe market for making batteries of twoor more Electric cells. Place the cells inthem properly, such that the positiveterminal of one cell is connected to thenegative terminal of the next a piece of wire each to the twometal clips on the cell holder as shownin Your battery is ready symbol used for representing abattery is shown in us now draw a circuit diagram ofan Electric circuit using symbols shownin Table the Electric circuit shown inFig.

5 You used a similar circuit inClass VI to make an Electric bulb you remember that the bulb glowsonly when the switch is in the ON position? The bulb glows as soon asthe switch is moved to the ON position. Copy this Electric circuit in yournotebook. Make also a circuit diagramof this circuit using symbols for thevarious Electric your diagram similar to the oneshown in Fig. is much easier to draw a circuitdiagram using symbols. Therefore, wegenerally represent an Electric circuit byits circuit shows another circuitdiagram. Is it identical to the circuitdiagram shown in In whichway is it different?Would the bulb glow in this electriccircuit? Recall that the bulb glows onlywhen the switch is in the ON positionand the Electric circuit is A cell holderFig.

6 Another type of cell holderPaheli and Boojho wonder whetherthe batteries used in tractors, trucksand inverters are also made from why is it called a battery? Canyou help them to find the answer tothis question? Fig. Truck battery and its cutout2022-23 Electric Current AND ITS EFFECTS163electric Current passes through it. Whenthe bulb gets fused, its filament Circuit diagram of Electric circuitshown in Fig. Another circuit diagramIf the filament of the bulb is broken,would the circuit be complete? Wouldthe bulb still glow?You might have noticed that aglowing Electric bulb become warm. Doyou know why? HEATING EFFECT OF ELECTRICCURRENTA ctivity an Electric cell, a bulb, a switchand connecting wires. Make an electriccircuit as shown in Thisactivity has to be done using only onecell.

7 Keep the switch in the OFF Fig. An Electric circuitIn the bulb there is a thin wire, calledthe filament, which glows when anCAUTIONN ever touch a lighted Electric bulbconnected to the mains. It may be veryhot and your hand may get burntbadly. Do not experiment with theelectric supply from the mains or agenerator or an inverter. You may getan Electric shock, which may bedangerous. Use only Electric cells forall the activities suggested here. Notice that the key or switch canbe placed anywhere in the circuit. When the switch is in the ON position, the circuit from thepositive terminal of the battery tothe negative terminal is circuit is then said to be closedand the Current flows throughoutthe circuit instantly. When the switch is in the OFF position, the circuit is is said to be open.

8 No currentflows through any part of Does the bulb glow? Touchthe bulb. Now move the Electric switchto the ON position and let the bulb glowfor a minute or so. Again touch the you feel any difference? After movingthe switch back to the OFF position,touch the bulb a circuit as shown in about 10 cm long piece of nichromewire and tie it between the nails. (Youcan get nichrome wire from an electricrepair shop or you can use a piece ofdiscarded coil of an Electric heater.)Touch the wire. Now switch on thecurrent in the circuit by moving theswitch to the ON position. After a fewThe wire gets hot when an electriccurrent passes through it. This is theheating effect of the Electric you think of any Electric appliancewhere the heating effect of the electriccurrent is used?

9 Make a list of touch the wire. (Do not hold itfor a long time.) Switch off the the wire again after a might have seen an electricroom heater or an Electric heater usedfor cooking. All these contain a coil ofwire. This coil of wire is called anelement. You may have noticed thatwhen these appliances are switched onCAUTIONDo not keep the switch in the ON position for a long time, otherwise thecell may become weak very could not see element in anelectric iron. Paheli told him thatelectrical appliances, such asimmersion heaters, hotplates, irons,geysers, Electric kettles, hair dryers,have elements inside them. Have youever seen the element in anyappliance?Fig. Element of Electric iron2022-23 Electric Current AND ITS EFFECTS165after connecting to the Electric supply,their elements become red hot and giveout amount of heat produced in awire depends on its material, lengthand thickness.

10 Thus, for differentrequirements, the wires of differentmaterials and different lengths andthicknesses are wires used for making electriccircuits do not normally become hot. Onthe other hand, the elements of someelectric appliances become so hot thatthey are easily visible. The filament ofFig. Glowing filament of an Electric bulb(incandescent)Incandescent Electric bulbs (Fig. ) are often used for lighting but they alsogive heat. It means that a part of electricity consumed is used in producingheat. This is not desirable as it results in the wastage of electricity. The fluorescenttube-lights and compact fluorescent lamps (CFLs) are better electricity efficientlighting sources. Nowadays, the use of light emitting diode (LED) bulbs isincreasing. For producing a given intensity of light, LED bulbs consume lesselectricity as compared to incandescent bulbs or fluorescent tubes or bulbs are much electricity efficient and therefore being Electric bulb, tube-light, CFL and LEDIt is advised to use electrical appliances and gadgets, which are electricity of Indian Standards, New Delhi assigns a Standard Mark on products,called ISI mark which is an assurance of conformity to the specificationsgiven on the products.