5. C h p t e r t G l n c e When electric current is pssed through conductor, it produces mgnetic field round it. The first discovery of the connection between electricity nd mgnetism ws mde by H. C. Oersted. The region round mgnet in which the force of ttrction nd repulsion exists is clled s mgnetic field nd it is represented by mgnetic lines of force or mgnetic field lines. Mgnetic lines of force re crowded where the mgnetic field is strong nd fr from ech other where the field is wek. Mgnitude of the field produced t given point is directly proportionl to the mgnitude of the current pssing in the conductor. Direction of the mgnetic field due to current crrying conductor is specified by Right hnd thumb rule. A coil of mny turns of insulted copper wire wrpped in the shpe of cylinder is clled solenoid. A solenoid hs ll the properties of the field produced by br mgnet. With the help of solenoid we cn mgnetise piece of rod of given mteril. If the rod is hrd steel nd if the mgnetic field is strong enough, permnent mgnet cn be produced. French scientist Ampere demonstrted tht current crrying conductor plced in mgnetic field will experience force nd the direction of this force will be given by Fleming's left hnd rule. Electric motor works on the principle tht current crrying conductor plced in mgnetic field experiences force. Michel Frdy mde n importnt discovery tht motion of mgnet with respect to coil or chnging mgnetic field cn induce n e.m.f. nd produce n induced current in the circuit. This is known s electromgnetic induction nd the direction of the induced current is given by Fleming's right hnd rule. Electric genertor works on the principle of electromgnetic induction. AC genertor produces lternting current nd DC genertor or dynmo produces direct current. In our houses we receive AC electric power of 220 V 250 V with frequency of 50 Hz. One of the wires in the domestic electric circuit is live wire with red insultion nd the other is neutrl wire with blck insultion. The third is the erth wire with green insultion which is connected to copper plte nd buried deep inside the erth. Erthing is used s sfety mesure to ensure tht ny lekge of current to metllic body does not give ny severe shock to user. An electric fuse is sfety device used for protecting the circuits nd electricl pplinces due to short circuiting or over loding.
SCIENCE & TECHNOLOGY - S.S.C. 8 9 MULTIPLE CHOICE QUESTIONS (MCQ's) (Ech question crries one mrk) MCQ's BASED ON CHAPTER Moderte Level 1. Mgnetic lines of force is the pth long which the unit : south pole moves in mgnetic field c south pole moves wy from the mgnetic field d north nd south poles move in mgnetic field 2. Like mgnetic poles : repel ech other b north pole moves in mgnetic field b ttrct ech other c neither ttrct nor repel d repel nd then ttrct 3. The reltion between electricity nd mgnetism ws first estblished by : Joule b Ohm c Oersted d Fleming 4. The direction of the mgnetic field round stright conductor crrying current is given by : Fleming's right hnd rule b Fleming's left hnd rule c right hnd thumb rule d none of these 5. Wht is the frequency of AC in Indi? 150 Hz b 100 Hz c 1000 Hz d 50 Hz 6. A coil of mny circulr turns of wire wrpped in the shpe of cylinder forms : conductor b solenoid c insultor d toroid 7. Which french scientist demonstrted the force on current crrying conductor in mgnetic field? Andre Mrie Ampere b Michel Frdy c Hns Oersted d George Ohm 8. The director of force on current crrying conductor in mgnetic field is given by : right hnd thumb rule b Fleming's left hnd rule c Fleming's right hnd rule d none of these 9. Which of the following is the lloy of luminium, nickel nd coblt? steel b nipermg c lnico d durlumin 10. Electromgnetic induction ws first studied by : Michel Frdy b C. V. Rmn c Hns Oersted d Andre Ampere 11. The direction of induced current by the mgnetic field in conductor is given by : Fleming's right hnd rule b Fleming's left hnd rule c right hnd thumb rule d none of these 12. Wht is the PD in domestic electric circuit between the live wire nd neutrl wire? 100 V 120 V b 150 V 200 V c 250 V 300 V d 220 V 250 V
90 Unique MCQ's Elementry Level 1. Which of the following doesn't work on electromgnetism? electric door bell b genertor c microphone d electric Oven 2. In br mgnet, mgnetic field lines strt from : north pole b south pole c centre of the mgnet d both the poles 3. Which of the following is n incorrect sttement? mgnetic field is strong t poles b mgnetic lines of force re closed curves c mgnetic lines of force intersect ech other d the tngent to the mgnetic lines of force gives the direction of the mgnetic field 4. The mgnetic lines of force due to stright conductor re : closed curves b semi circles c concentric circles d stright lines 5. The mgnetic field produced due to current through circulr loop depends directly on : resistnce of the wire b rdius of the loop c current pssing through it d thickness of the wire 6. The mgnetic field produced by given current in the conductor decreses s the distnce from the conductor : increses b decreses c doubles d remins sme 7. Which of the following is device used for producing current? voltmeter b mmeter c glvnometer d genertor 8. At the time of short circuit, the current in the circuit : increses b increses in steps c remin sme d decreses 9. The direction of current in the rmture coil of electric motor is reversed by : brushes b bttery c mgnet d commuttor 10. The device used for converting electric energy to mechnicl energy is : genertor b motor c glvnometer d voltmeter 11. The presence of current in circuit is detected using : glvnometer b mmeter c voltmeter d genertor 12. On which principle does the Electric genertors work? Joule's lw b heting effect of current c electromgnetic induction d force on current crrying conductor in mgnetic field 13. Which re the two min orgns in the humn body where the mgnetic field produced is significnt? liver nd pncres b lungs nd stomch c kidney nd intestine d hert nd brin 14. Which of the following doesn't belong to the group? direct current b commuttor c brushes d rmture coil 15. Which of the following is not sfety mesure in using electricity? electric fuse b solenoid c insulting mteril d rubber shoes
SCIENCE & TECHNOLOGY - S.S.C. 9 1 Complex Level 1. A compss needle gets deflected when brought ner br mgnet becuse: it hs pointed ends b it is tiny br mgnet c it is mde of iron d it is suspended freely 2. Motion of the conductor is mximum when the direction of the current is: t 90º to the mgnetic field b sme to the mgnetic field c t 180º to the mgnetic field d just opposite to the mgnetic field 3. The direction of induced current in n AC genertor chnges once in ech: two revolutions b one revolution c hlf revolution d one fourth revolution 4. The lloy of iron, nickel, luminium nd titnium; durlumin b steel c lnico d nipermg 5. The technique of obtining imges of humn orgns using mgnetism is clled: PET scn b MRI c USG d CT scn 6. Wht is required for the production of current by electromgnetic induction? both coil nd mgnet must be sttionry b coil nd mgnet must be in reltive motion c mgnetic field should be constnt d glvnometer should be deflected 7. The phenomenon of electromgnetic induction is the process of : chrging body b generting mgnetic field c generting electric current d exerting force on the conductor 8. Wht is the frequency of direct current (DC)? 50 Hz b 150 Hz c 0 Hz d 100 Hz 9. Which of the following is not component of DC genertor? rmture coil b strong mgnets c slip rings d brushes 10. Phse wire is lso known s : insulted wire b live wire c neutrl wire d erth wire Mysterious Level 1. Which of the following work on electromgnetism? thermometer b mmeter c geyser d electric iron 2. During short circuit, the resistnce of the circuit becomes : zero b very smll c very lrge d constnt 3. The mgnetic field produced t the centre of circulr loop is inversely proportionl to : resistnce of the wire b mgnitude of the current c rdius of the loop d time for which the current psses 4. The field lines inside solenoid re in the form of : prllel stright lines b closed curves c concentric circles d semicircles
92 Unique MCQ's 5. If there is circulr coil of 'n' turns nd the mgnetic field produced by single turn is 'x', wht is the totl field produced? n x b n x c n + x d x n 6. An electron enters mgnetic field t right ngles to it s shown in the figure. Wht will be the direction of force cting on the electron? Mgnetic field to the right b to the left c out of the pge d into the pge 7. In stright wire B, current is flowing in the verticlly downwrd direction. Wht will be the direction of mgnetic field lines round it? upwrd b downwrd c clockwise d nti clockwise MCQ's BASED ON CHAPTER Moderte Level Elementry Level Complex Level Mysterious Level Answers 1 - b 2-3 - c 4 - c 5 - d 6 - b 7-8 - b 9 - c 10-11 - 12 - d 1 - d 2-3 - c 4 - c 5 - c 6-7 - d 8-9 - d 10 - b 11-12 - c 13 - d 14-15 - b 1 - b 2-3 - c 4 - d 5 - b 6 - b 7 - c 8 - c 9 - c 10 - b 1 - b 2 - b 3 - c 4-5 - b 6 - d 7 - c Electron