Multiple choice questions (1) 1 Tesla = (c) NA -1 (d) NA -1 m -2

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1 Multiple chice questins (1) 1 Tesla = (a) N Am -1 (b) NA -1 m -1 NA -1 (d) NA -1 m - () Tw parallel straiht wires carryin currents in ppsite directin (a)repel each ther (b) attract each ther N effect prduce Manetic flux and manetic flux density are related as (3) Directin f manetic flux is (a) nrmal t the surface (b) parallel t the surface at any anle (d) n directin (4) The relatin f B r is called (a) Faraday s law (b) Gauss s law Ampere s law (d) Lenz law (5) The unit f manetic flux is called (a) tesla (b) Weber auss (6) Accrdin t Ampere s circuital law the manetic field aln the axis f slenid with n number f turns per unit lenth is iven by (a) (b) B n B n (d) B n B (7) The directin f frce experience by a chared particle mvin in a manetic field will be (a) parallel t the field (b) ppsite t the field parallel t its directin (d) perpendicular t bth the field and velcity vectr (8) When a chared particle mves thruh a manetic field, the effect f the field chanes the particles (a) speed (b) mass enery (d) directin (9) The frce F = F e + F m in the equatin is called (a) deflectin frce (b) restrin frce Lrentz frce (1) Wrk dne by manetic frce is (a) maximum (b) Fm dcs zer (d) Fm dsin (11) f F m = Fe, then the velcity f chare particle is (a) = EB E (b) B B E (1) When a chare particle enters a manetic field it will mve n a circular path f radius qb mv (a) r (b) r mv qb qmv (d) qmb B r (13) e m is minimum fr (a) electrn helium nuclei (b) prtn (d) neutrn (14) e m is maximum fr (a) electrn (b) prtn helium nuclei (d) neutrn (15) The value f e/m f an electrn (a) 9.43 x 1-19 Ck -1 (b) 9.43 x 1-31 Ck x 1 11 Ck -1 (d) 9.43 x 1-7 Ck -1 (16) The vltae applied acrss X plates displaces the spt aln x-axis and displacement is prprtin t (a) vltae (b) current 1 By: Prf. Muhammad Amin

2 time (d) all f these (17) The functin f rid in CO (a) cntrls the number f electrns accelerated by ande (b) cntrls the brihtness f spt frmed n the screen bth a and b (18) Electric ptential n rid is (a) psitive (b) neative zer (19) The trque actin n a cil is maximum when plane f cil is (a) parallel t B (b) perpendicular tb antiparallel t B () f s the anle between the directin f B and nrmal t the plane f the cil, then trque n the rectanular cil is (a) NBA Cs (b) NAB Sin NAB tan (1) f the plane f the current carryin cil with N turns f area A, makes an anle with the manetic inductin B, the trque n the cil is (a) NBA Cs (b) NAB Sin NAB tan () The alvanmeter in which the cil cmes t rest quickly after the current passed thruh it r the current is stpped frm flwin thruh it is called (a) stable alvanmeter (b) dead beat alvanmeter bth a and b (3) The alvanmeter in series with a hih resistance acts as a (a) vltmeter (b) hm meter ammeter (d) CO (4) The sensitivity f a alvanmeter can be increased by (a) decreasin the area f the cil (b) increasin the manetic field decreasin the number f turns (d) all f these (5) The shunt resistance is iven by (a) s (b) s s By: Prf. Muhammad Amin (d) s (6) T cnvert the alvanmeter int vltmeter the hih resistance is iven by (a) h (b) h h (d) h (7) T increase the rane f vltmeter the series resistance is (a) increased (b) cnstant decreased (8) Diital versin f Avmeter is called (a) diital multimeter (b) diital ammeter diital rectifier (d) diital vltmeter (9) DMM stands fr (a) diital ammeter (b) diital multimeter diital measurin meter (d) diital vltmeter (3) The switch used in current measurin part f AO meter fr measurin f different currents is called (a) rane switch (b) pwer switch selective switch (d) all f these (31) When chared particle enters in a manetic field, at an anle ther then 9, then it mves in (a) circular path (b) straiht line randm frm (d) helical path (3) The field inside the slenid is as cmpare t utside the slenid (a) weak (b) strn

3 zer (33) The e/m f a prtn is (a) Same as electrn (b) smaller then electrn Greater than electrn (d) all f these (34) The electrn un in CO cnsists f (a) Grid (b) indirectly heatin cathde Three andes (d) all f these (35) n CO the rid is at w.r.t andes. (a) psitive ptential (b) neative ptential bth a and b (d) zer ptential (36) The prtin f the alvanmeter whse mtin causes the needle t mve acrss the scale is (a) meter bride (b) side wire bride meter mvement (37) A chared particle is prjected at an anle int a unifrm manetic field. Which is f the fllwin parameters f the chared particle will be affected by the manetic field: (a) Enery (b) Mmentum Speed (d) elcity (38) A chared particle mvin in manetic field experiences a manetic frce iven by. (a) F m = q( x B ) (b) F m = q B F m = ( x B )/q (d) F m = (. B )q (39) f current flws frm tp twards bttm thruh a wire then directin f lines f frce wuld be: (a) Parallel t the wire (b) Perpendicular t wire Clckwise (d) Anti-clckwise (4) T measure the current in a circuit, ammeter is always cnnected in (a) Parallel (b) series Smetimes parallel smetimes series (d) neither parallel nr series (41) Shunt resistance is called (a) by pass resistr (b) specific resistr reactance (d) impedance (4) A vltmeter is always cnnected in: (a) parallel (b) series perpendicular (d) straiht line (43) A manetic frce is simply a (a) reflectin frce (b) deflectin frce restrin frce (d) ravitatinal frce (44) The sensitivity f a alvanmeter can be increased by (a) decreasin the area f the cil (b) decreasin the number f turns f the cil increasin the manetic field (d) usin a fine suspensin (45) A manetic field acts n a chared particle s as t chane its (a) speed (b) enery directin f mtin (d) all f these (46) A current carryin cil placed in unifrm manetic field experiences maximum trque when anle between plane f cil and manetic field is (a) (b) 45 6 (d) 9 (47) Manetic field B = 4i +18k Wbm - passes thruh 5k m area. Net flux thruh the area is (a) Wb 9 Wb (b) 91 4 Wb (d) Zer (48) Manetic frce n a mvin chared particle is perpendicular t the (a) Manetic field (b) Electric field elcity f the particle d) manetic field and velcity f the particle (49) The ande in the CO is (a) Cntrl n. f wave (b) Cntrl brihtness f spt frmed Accelerates and fcus the beam (d) At neative ptential with respect t cathde (5) One Weber is equal t (a) NA 1 (b) Nm 1 A NmA 1 (d) Nm 1 A 1 By: Prf. Muhammad Amin 3

4 (51) f finers r riht hand shw the directin f manetic field and palm shws the directin f frce then thumb pints fr (a) trque (b) vltae current (d) induced emf (5) Cathde ray scillscpe wrks by deflectin a beam f: (a) Neutrns (b) Prtns Electrns (d) Psitrns (53) Sensitivity f a alvanmeter can be increased by ;- (a)decreasin the value f tensinal cuple. (b) Decreasin number f turns. Decreasin area f plane f cil. (d) Decreasin manetic field. (54) The S. unit f manetic permeability is (a) Wb (b) Wb Wb (d) Wb (55) When Ohm meter ives full scale deflectin it indicates (a) zer resistance (b) infinite resistance A m 1 1 m ma 1 small resistance (d) very hih resistance (56) When a chared particle is prjected perpendicularly in a manetic field, its trajectry is (a) Hyperbla (b) Parabla Helix (d) Circular (57) e/m f an electrn is (a) Br Br (b) (d) Br Br (58) The alvanmeter can be made sensitive if the value f the factr C BNA (a) Made lare (b) Made small emains cnstant (d) infinite (59) An electrn f mass m and chare e is mvin in a circle f radius r with speed v in a unifrm manetic field f strenth B. then (a) r m (b) r B is 1 r v (6) The field inside the Slenid is iven by ( (a) (b) n n (d) N n (d) 1 r m Am 1 SHOT QUESTONS 14.1 A plane cnductin lp is lcated in a unifrm manetic field that is directed aln the x-axis. Fr what rientatin f the lp is the flux a maximum? Fr what rientatin is the flux a minimum? Ans: When the plane f the lp is placed aln the manetic field B, flux thruh the lp is minimum. As, When 9 S, BACs Then ABCs Cs 9 9 When the plane f the lp is placed perpendicular t manetic field B, flux thruh lp is maximum. As, BACs When S, Then ABCs Cs BA A current in a cnductr prduces a manetic field, which can be calculated usin Ampere s law. Since current is defined as the rate f flw f chare, what can yu cnclude abut the manetic field due t statinary chares? What abut mvin chares? Ans: Field arund statinary chare is nly electric field. Fr a statinary chare, the rate f flw f chare is zer. s there will be n manetic field due t statinary chare. We knw that manetic field is prduced By: Prf. Muhammad Amin 4

5 arund a current carryin cnductr. As current () in cnductr is due t mtin f chares therefre it is cncluded that manetic field is als prduced in additin t electric field arund mvin chares Describe the chane in the manetic field inside a slenid carryin a steady current, if (a) the lenth f the slenid is dubled but the number f turns remains the same and (b) the number f turns is dubled, but the lenth remains the same. Ans: We knw that manetic field in a current carryin cnductr is iven as, (a) B n N n l N B l as lenth is dubled N B l 1 B B This shws that manetic field is halved. (b) When number f turns are dubled N B l By dublin turns N B l B B S manetic field is dubled 14.4 At a iven instant, a prtn mves is the psitive x directin in rein where there is manetic field in the neative z directin. What is the directin f the manetic frce? Will the prtn cntinue t mve in the psitive x directin? Explain. Ans: ur is in x-directin B ur is in ve z-directin By usin the riht hand rule in frmula F = q( B) r ur ur.the directin f F r is aln y-axis. t will be deflected aln y-axis and will trace a curved path in x-y plane Tw chared particles are prjected int a rein where there is a manetic field perpendicular t their velcities. f the chares are deflected in ppsite directins, what can yu say abut them? Ans: We knw Fr (+ve chare) F q( B) Fr (-ve chare) F q( B) Here we can say that directin f deflectin f psitive chare is ppsite t the directin f deflectin f neative chare. Therefre when particles are deflected in ppsite directin, ne is psitively chared and the ther is neatively chared Suppse that a chare q is mvin in a unifrm manetic field with a velcity v. why is there n wrk dne by the manetic frce that acts n the chare q? Ans: suppse a chare q is mvin in a unifrm manetic field with a velcity v. The manetic frce acts n the chare. This frce will always act at riht anle t the velcity v r directin f mtin s, 9 W F d W FdCs W FdCs9 W S the wrk dne by the manetic frce is zer. By: Prf. Muhammad Amin 5

6 14.7 f a chared particle mves in a straiht line thruh sme rein f space, can yu say that the manetic field in the rein is zer? Ans: f the chared particle mves in a straiht line thruh sme rein f space then there are tw pssibilities. (i) There exists n manetic field in the rein. (ii) A manetic field exists but particle is mvin aln the manetic field and we knw that n manetic frce acts n a particle mvin aln the manetic field B 14.8 Why des the picture n a T screen becme distrted when a manet is bruht near the screen? Ans: The picture n a T screen is frmed by the beam f electrns. When a manet is bruht near the screen it disturbs the beam f electrns. As a result the picture n a T screen becmes distrted s it pssible t rient a current lp in a unifrm manetic field such that the lp will nt tend t rtate? Explain. Ans: We knw that trque actin n a current carryin cil placed in manetic field is iven by, NAB Cs ( is anle between plane and B) f 9 then ( Cs9 ) i.e if plane f cil is perpendicular t the manetic field then n trque acts upn it Hw can a current lp be used t determine the presence f a manetic field in a iven rein f space? Ans: A current carryin lp behaves as a manet because when current is passed thruh the lp then nrth and suth ples are established at its tw faces. When a current carryin lp is placed in a manetic field then it is deflected. ts deflectin shws the presence f manetic field in the rein Hw can yu use a manetic field t separate istpes f chemical element? Ans: stpes f a chemical element cntain same chare n. but different mass n. when the istpes f a chemical element are prjected perpendicularly in a manetic field, they bein t mve in different circular paths due t the difference in their mass numbers. Manetic frce prvide the necessary centripetal frce t these istpes. Fm Fc mv Be r mv r Be r m ( and B are cnstants) S they can be separated n the basis f their radii in the manetic field What shuld be the rientatin f a current carryin cil in a manetic field s that trque actin upn the cils is (a) maximum (b) minimum? Ans: We knw that trque actin n a current carryin cil placed in manetic field B is iven by. NAB Cs( is anle between plane and B) (a) f plane f cil is parallel t manetic field then NAB Cs NAB ( Cs=1) max imum (b) f plane f cil is perpendicular t manetic field then NB Cs 9 ( Cs 9 ) minimum A lp f wire is suspended between the ples f a manet with its plane parallel t the ple faces. What happens if a direct current is put thruh the cil? What happens if an alternatin current is used instead? Ans: f a lp f wire is suspended between the ples f a manet with its plane parallel t the ple faces then the anle between plane f cil and manetic field is 9. We knw that trque actin n a current carryin lp placed in a manetic field is iven as NAB Cs n this case = 9 ( Cs9 ) By: Prf. Muhammad Amin 6

7 This shw that the cil will nt rtate whether passes direct current r alternatin current Why the resistance f an ammeter shuld be very lw? Ans: Ammeter is an instrument used t measure current. t is always cnnected in series in a circuit. Therefre resistance f ammeter is added in circuit and current in a circuit decreases. Fr accurate measurement f current (), resistance (), f ammeter shuld be lw s there is n appreciate chane in resistance f circuit s (current) can be measured accurately. An ideal ammeter have zer shunt resistance Why the vltmeter shuld have a very hih resistance? Ans: ltmeter is instrument used t measure ptential difference and always cnnected in parallel in a circuit. The resistance f vltmeter shuld be very hih s that it may draw a very small value f current frm the circuit, therwise, it will lad the circuit and chane the ptential difference which is required t be measured. An ideal vlt meter have infinite resistance. ADTONAL SHOT QUESTONS (1) What is the difference b/w flux density and flux? Ans: FLUX DENSTY * Ttal number f lines passin thruh a unit area, if area is perpendicular t the manetic field lines * t is represented by B * t is represented by * e B if A * e B A * ts S unit is wbm - * ts S. unit is wb FLUX * Ttal number f lines f frce passin thruh a certain area knwn as flux. () What is meant by sensitivity.hw the sensitivity f a alvanmeter be increased? Ans: Sensitivity f a alvanmeter is defined as Deflectin f alvanmeter per unit current Since C BAN θ / = B A N /C Hence, alvanmeter can be made mre sensitive, f (i) ncrease B (ii) ncrease A (iii) ncrease N (iv) Decrease C (8) Hw a alvanmeter can be cnverted int vltmeter? Ans: When a wire f hih resistance h is cnnected in series with a alvanmeter, then such arranement is called vltmeter. Hih resistance is attached t draw minimum current frm the circuit and its value is iven as h = -. ltmeters always cnnected in parallel in a circuit (9) Hw a alvanmeter can be cnverted int an ammeter? Ans: When a wire f lw resistance s. is cnnected in parallel with a alvanmeter, then arranement frmed is called ammeter. Lw resistance wire called shunt resistance is attached t increase the rane f alvanmeter. The value f s. is iven as s = the ammeter is always used in series in a circuit. - (1) What are the cmpnents f electrn un f C..O. e By: Prf. Muhammad Amin 7

8 Ans: Electrn un cnsists f filament F which heats cathde C which emits electrns. Three andes A 1,A and A 3 which are at hih psitive ptential with respect t cathde C, accelerates and fcuses the electrn beam n a screen S lastly cntrl rid G, which is in frnt f cathde C and is at neative ptential with respect t cathde, cntrl the number f electrns r the brihtness n screen. (16) What are the uses f CO? Ans: USES OF CO: The CO is used fr displayin the wavefrm f a iven vltae. Once the wavefrm is displayed, we can measure the vltae, its frequency and phase. As the y-axis is calibrated in vlts and the x-axis in time; we can easily find the instantaneus value and peak value f the vltae. With the help f time axis, we can determined the time perid f the wave. t is used t btained infrmatin abut phase difference between tw vltaes by displayin their wavefrms. (17) What is a stable r Dead beat alvanmeter? Ans: Such a alvanmeter in which the cil cmes t rest quickly after the current passed thruh it r the current is stpped frm flwin thruh it is called stable r dead beat alvanmeter. (18) What is Lrentz frce and hw can it be frmulated? Ans: Lrentz Frce: Frce actin n a chared particle mvin in an electrmanetic field is called Lrentz frce. Frmulatin: f q is the chare n particle mvin in a rein where electric field E and manetic field are simultaneusly present, then q E is electric frce & q B is the manetic frce. ectr sum f these frces is knwn as Lrentz Frce n that chare q. F qe q B B Here is velcity f the chare in the electrmanetic field. By: Prf. Muhammad Amin 8