17 MAGNETIC EFFECT OF ELECTRIC CURRENT

1 NotesMODULE - 4 Energy 393 MAGNETIC EFFECT of ELECTRIC CurrentSCIENCE AND TECHNOLOGY17 MAGNETIC EFFECT OFELECTRIC CURRENTIn the earlier lesson you have learnt that, electricity is an important part in today sworld of industrialization. Our life is incomplete without it. Whether we work in anoffice or at home, every thing depends upon the availability of electricity. Applianceslike the ELECTRIC bulb, fan, television, refrigerator, washing machine, motor, radio,everything works due to ELECTRIC CURRENT passes through CURRENT carrying conductor or coil then amagnetic field is produced around it. The working of appliances like ELECTRIC bell isbased on this principle. As opposite to this if a continuous change in MAGNETIC fieldis produced then ELECTRIC CURRENT can be produced. This is how electricity andmagnetism have become synonymous today. Transmission of ELECTRIC CURRENT takesplace from the distant electricity generation stations through high tension wires,through transformers to homes.

2 This chapter deals with the meaning of safe use ofelectricity. Along with this the same concepts related to magnetism are explainedthrough simple activities that one can perform on their studying this lesson you will be able to: identify magnets and explain their properties; explain the concept of MAGNETIC field and state the properties of lines ofmagnetic force; infer that when electricity flows through a conductor, MAGNETIC field isproduced around it; describe electro-magnets and explain the working of ELECTRIC bells; explain the force experienced by a CURRENT carrying conductor placed in amagnetic field ;NotesSCIENCE AND TECHNOLOGYMODULE - 4 MAGNETIC EFFECT of ELECTRIC CurrentEnergy 394 describe electromagnetic induction and its importance in different aspectsof daily life; describe alternate CURRENT (AC) and direct CURRENT (DC) currents and listthe appliances that work on these currents; state the hazards involved in using electrical energy in industries and athome and describe safety measures necessary to minimize AND ITS PROPERTIESM agnet has always been a thing of awe use and attraction for humans.

3 Accordingto history, the use of magnets were discovered by the ancient Greeks during theperiod of Greek Natural magnetThey found stones which were able to attract iron and nickel like other naturally occurring stones (see Fig. ) which was discovered then is calledas lodestone . This is an oxide of iron (Fe3O4). The property of attraction of smallparticles of iron towards lodestone is called as magnetism . It has been often seenthat the MAGNETIC force of attraction of these natural magnets is much less and thus,these magnets cannot be use for practical purposes. Strong magnets made of iron,nickel and lead are made artificially and used for practical purposes. Those magnetsare also called as permannent magnet. So, a magnet is a material or object thatproduces a MAGNETIC field which is responsible for a force that pulls or attacts onother strong magnets can be made in various shapes and creats its own persistentmagnetic field . The magnets that are commonly available in different shapes are:(a) Bar magnet(b) Horseshoe magnet(c) Cylindrical magnet(d) Circular magnet(e) Rectangular magnetNotesMODULE - 4 Energy 395 MAGNETIC EFFECT of ELECTRIC CurrentSCIENCE AND TECHNOLOGYFig.

4 Magnets of different shapesHave you ever observe magnets of any of above shapes arround you? These magnetsof different shapes are used in various appliances used at home like tape recorder,radio, motor, door-bell, head phones etc. These magnets are used in variousappliances to either hold or separate, control, elevate (lift) substances, changingelectrical energy to mechanical energy (motors, loudspeakers) or mechanical toelectrical energy (generators and microphones).If a natural magnet is suspended freely with the help of a string, it always rests inthe north-south direction. If the magnet is slightly turned from this direction, it stillreturns to the same. The end that rests towards the north is named as North Pole while the one which ends at south is named as South Pole. They are representedas N and S .ACTIVITY one MAGNETIC needle, two bar magnets, some iron filling, an alpin and do theexperimental study of properties of step may followed:1. Tie a string at the middle of a bar magnet and hang it with the help of a bar always rests at the same direction.

5 With the help of the MAGNETIC needle,CircularMagnetCylindricalMagnetRe ctangularMagnetHorse ShoeMagnetBar MagnetNotesSCIENCE AND TECHNOLOGYMODULE - 4 MAGNETIC EFFECT of ELECTRIC CurrentEnergy 396find out the direction. By this you will be able to prove that a bar magnet alwaysrests in the north-south (i)2. Take iron fillings near the bar magnet. They stick to the magnet. Thus, magnetattracts iron. You would observe that the amount of iron fillings near the polesis maximum while at the middle is (ii)3. If you bring any pole of a bar magnet near the pole of a freely suspended barmagnet, then either it will attract or repel the same. Opposite poles of a magnetattract each other while like poles (north-north or south-south) repel each (iii)NotesMODULE - 4 Energy 397 MAGNETIC EFFECT of ELECTRIC CurrentSCIENCE AND TECHNOLOGY4. Take an iron alpin near a bar magnet leave it there for sometime. You will findthat the alpin has acquired MAGNETIC properties and iron fillings start sticking tothe ends of the alpin as (iv)5.

6 Break the bar magnet into smaller pieces. Now observe that MAGNETIC propertiesare retained in the pieces as well. Thus, the two poles of a magnet cannot (v) Properties of MagnetsThrough the activity we can list the properties of MAGNETIC as follows:1. Attracts iron towards Freely suspended magnet always rests at the north-south Like poles repel while unlike poles If iron pieces are brought near a strong magnet they also start behaving The poles of a magnet cannot be MAGNETIC FIELDKeep a small MAGNETIC needle near a bar magnet. The MAGNETIC needle rotates andstops in a particular direction only. This shows that a force acts on the MAGNETIC needlethat makes it rotate and rest in a particular direction only. This force is called region around the magnet where the force on the MAGNETIC needle occurs andthe needle stops at a specific direction, is called a MAGNETIC field . The directionof MAGNETIC field is represented by MAGNETIC line of forces. As shown in Fig.

7 (i),NotesSCIENCE AND TECHNOLOGYMODULE - 4 MAGNETIC EFFECT of ELECTRIC CurrentEnergy 398the direction of MAGNETIC needle changes continuously and it takes the curved pathwhile moving from north to south. This curved path is known as MAGNETIC line offorces. Tangent line draw at any point on MAGNETIC line of force, represent the directionof MAGNETIC field at that point. These MAGNETIC line of forces have following properties:1. MAGNETIC line of forces always start from north pole and end at south pole ofthe These line of forces never intersect each Near the poles MAGNETIC lines are very near to each other which shows thatmagnetic field at the poles is stronger as compare to other (i)Our Earth itslef acts as a giant magnet with south MAGNETIC pole somewhere in theArctic and north MAGNETIC pole in Antaractic. The Earth alsobehaves like a bar magnet. It s hot liquid centre core containsiron and as it moves, it creates an ELECTRIC CURRENT that causea MAGNETIC field around the Earth.

8 The Earth has a north andsouth MAGNETIC pole. These poles are not same with thegeographic north and south poles on a map and tilted at anangle of degree with repect to it. Due to this, if a magneticneedle is suspended freely, it rests in the north-south directionand is useful for can also detect the presence of MAGNETIC field . For doing this take two barmagnets, one scale and follow the given steps:Fig. (ii)NotesMODULE - 4 Energy 399 MAGNETIC EFFECT of ELECTRIC CurrentSCIENCE AND TECHNOLOGY1. Keep two bar magnets in such a way that they are laid on the same line andin same plane at a distance of 10 Bring the like poles slowly towards each other. Could you feel something?3. You will feel two poles are repelling each Change the orientation of one of the bar magnets so that opposite poles faceeach other. You would observe that the two magnets quickly come close togetherdue to force of attraction between this we can conclude that force acts between the magnets and the region aroundthe magnets in which this force may be experienced is called the MAGNETIC field .

9 Fig. QUESITONS Define magnet and list its properties?2. What happen, with the properties of magnet when it is broken into two pieces?3. Name the part of telephone where magnet is used?4. Hang the bar magnet with the string, it will always rest in which directions(i) East-west(ii) West-south(iii)North-south(iv)North-east 5. Do MAGNETIC field exist throughout space?6. The north pole, MAGNETIC needle points towards earth s(i) North pole(ii)South pole(iii)Centre(iv)None of the above7. What are MAGNETIC poles?NotesSCIENCE AND TECHNOLOGYMODULE - 4 MAGNETIC EFFECT of ELECTRIC CurrentEnergy field AROUND THE CURRENTCARRYING WIREIf an ELECTRIC CURRENT is made to flow in a wire, MAGNETIC field produce arround seeing this take a conducting wire (like copper). Now with the help of connectingwires attach this to the two ends of a battery. Keep a MAGNETIC needle parallel tothe conducting copper wire as shown in Fig. (a). When the circuit is completethe MAGNETIC needle shows deflection.

10 This shows that when ELECTRIC CURRENT flowsthrough a conductor, MAGNETIC field is produced around the conductor. If the currentis increased, there is greater amount of deflection. If the direction of flow of electriccurrent is changed (by reversing the end of the battery) the direction of deflectionin the MAGNETIC needle is also reversed. If the CURRENT flow is stopped the deflectionin the MAGNETIC needle also ceases. Thus MAGNETIC field is an EFFECT of flow of electriccurrent through conducting wire. In the year 1820 a scientist from Denmark Oersted observed this EFFECT for the first time.(a)(b)Fig. principle of the MAGNETIC EFFECT of ELECTRIC CURRENT used in many appliances likemotor ELECTROMAGNETAn electromagnet is a type of magnet in which MAGNETIC field is produced by theflow of elctric CURRENT . For making electromagnet take a piece of paper and givea cylindrical several turns of a copper wire over this from one end to the other. This iscalled solenoid a long thin loop of wire.