[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm MULTIPL CHOIC QUSTIONS (1) In carbn resistr the gld band indicates tlerance f (a) 5% (b) % 0% (d) 10% () The wrk dne t mve a psitive charge frm ne pint t anther pint given by (a) W Q V (b) V W Q Q W V 1 (d) W VQ (3) Which ne is used t determine the internal resistance f a cell (a) ammeter (b) vltmeter galvanmeter (d) ptentimeter (4) Slide wire bridge is practical frm f (a) ammeter (b) Wheatstne bridge galvanmeter (d) ptentimeter (5) The current flwing twards a pint is taken as (a) psitive (b) negative zer (d) neutral (6) Fr an pen circuit (a) = Vt (b) > Vt < Vt (d) = Vt + Ir (7) 1 J/C = (a) vlt (b) farad ampere (d) hm (8) A thermistr is heat sensitive (a) resistr (b) capacitr inductr (d) dide (9) The temperature cefficient f resistance f a material is expressed as t t (a) (b) t t t t (d) t t (10) If the resistances 1, and 3 are cnnected in series then their equivalent resistance is given by 1 1 1 1 (a) eq 1 3 (b) 1 3 eq 1 3 1 1 1 1 (d) eq 1 3 eq (11) Which instrument measure the ptential difference crrectly (a) CO (b) ptentimeter vltmeter (d) bth a and b (1) Tw resistrs each f value 10 hm are cnnected in series, the equivalent resistance will be (a) 10 Ω (b) 0 Ω 5 Ω (d) zer Ω (13) The resistance f silicn decreases with (a) increase in temperature (b) decrease in temperature increase in viscsity (d) decreases in velcity (14) Whenever current is drawn frm a cell, its terminal ptential difference and e.m.f. becme. (a) Different (b) Same Zer (d) Negative (15) A rhestat can perate as a: (a) Transfrmer (b) Amplifier Oscillatr (d) Ptential divider (16) The value f temperature cefficient f resistance f mst thermistrs is: (a) Psitive (b) Negative BY: Prf. Muhammad Amin 1
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm Zer (d) Infinity (17) If the cnductivity f a material is small then it is: (a) A cnductr (b) A pr cnductr A gd cnductr (d) An insulatr (18) The pwer utput f a lamp is 6 W. Hw much energy des the lamp give ut in minutes? (a) 3 J (b) 1 J 10 J (d) 70 J (19) lectrical energy is measured in (a) Watt (b) Hrse pwer Kilwatt (d) Kilwatt hur (0) Maximum pwer delivered by battery is (a) P max = 4r Pmax = VI (1) Pwer dissipatin is expressed by (a) V P = (b) Pmax = 4r (d) unlimited (b) P = V P = V (d) P = I () The algebraic sum f ptential changes fr a clsed circuit is: (a) Psitive (b) Negative Zer (d) greater than unity (3) Free electrns are: (a) tightly bund (b) fixed lsely bund (d) tightly fixed (4) Which ne is used t determine the internal resistance f a cell? (a) ammeter (b) vltmeter galvanmeter (d) ptentimeter (5) Siemen is the unit f (a) resistance (b) cnductance resistivity (d) cnductivity (6) The resistivity f a cnductr increases with (a) increase in its length (b) increase in its area increase in its temperature (d) decrease in its length (7) Current flws in the gases due t (a) electrns nly (b) electrns and ins psitive and negative ins (d) electrns and hles (8) The emf is always even when n current is drawn thrugh the battery f cell. (a) Zer (b) Present Absent (d) Maximum (9) The graphical representatin f Ohm s law is (a) Hyperbla (b) llipse Parabla (d) Straight line (30) A student has five resistances each f value 1. The minimum resistance that can be btained by 5 cmbining them in parallel is (a) 1 50 (b) 1 5 1 10 (d) 5 (31) The substance having negative temperature c-efficient is: (a) Carbn (b) Irn Tungsten (d)gld (3) esistivity at a given temperature depends upn : (a) Area f crss-sectin (b) Length Nature f material f cnductr (d) Bth length and area (33) Temperature c-efficient f esistivity permeability is (a) k (b) m 1 k (d) k (34) The drift velcity f an electrn in a cnductr in the presence f electric field is f the rder f 1 (a) 10 ms 3 1 (b) 10 ms 6 1 10 ms 7 1 (d) 10 ms (35) Specific resistance f a material depends upn: (a) Length (b) Area BY: Prf. Muhammad Amin
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm Temperature (d) Bth A & B (36) If the resistance f 500 have frth band f silver clur then its upper maximum resistance will be: (a) 600 (b) 550 450 (d) 400 (37) One Ohm is equal t: (a) VC -1 (b) CV -1 AC -1 (d) VA -1 (38) The temperature c-efficient f resistance fr Ge is (a) Psitive (b) Negative All f these (d) Nne f these (39) esistivity is reciprcal f (a) Cnductance (b) Cnductivity Inductin (d) Nne f these (40) Kirchff s first rule is manifestatin f law f cnservatin f (a) Mass (b) nergy Mmentum (d) Charge (41) Maximum pwer delivered by battery is (a) P max P max = 4r = VIt BY: Prf. Muhammad Amin 3 (b) P max = 4r (d) Unlimited (4) The drift velcity f electrns in a cnductr is f the rder f (a) 10-3 ms -1 (b) 10 - ms -1 10 3 ms -1 (d) 10-4 ms -1 (43) The heat prduced by the passage f current thrugh a resistr (a) H = I t 1 H= t (b) H = I t I H= t (44) A wire f unifrm area f crss sectin A and length L is cut int tw equal parts. The resistance f each part becmes (a) Duble (b) Half 4 time (d) ¼ time (45) A 100 watt bulb is perated by 00 vlt, the current flwing thrugh the bulb is (a) 0.5 A (b) 1 A A (d).5a (46) One culmb f charge is created by (a) 10 lectrns (b) 1.6 10-19 electrns 6.5 10 18 electrns (d) 6.5 10 1 electrns (47) The electrical analg f mass in electricity is (a) Capacitance (b) Inductance Charge (d) esistance (48) If the cnductivity f a material is high, then it is (a) An insulatr (b) A semi cnductr A gd cnductr (d) A super cnductr (49) Fr an pen circuit, the current flwing thrugh circuit will be: (a) Infinite (b) Finite Maximum (d) Zer (50) The clur f strips n a carbn resistr frm extreme left are yellw, black and brwn respectively its resistance is (a) 4K (b) 400 40 (d) 40 K (51) The terminal ptential difference f a battery f internal resistance r and emf is (a) V= + Ir (b) V = Ir ε r I V (d) I ε r (5) If the current thrugh a resistance is halved, then the (a) Pwer is halved (b) Heat dissipated is halved Ptential difference is halved (d) esistance is dubled
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm (53) lectrmtive frce is mst clsely related t: (a) lectric field Ptential energy (54) Charge carriers in electrlytes are: (a) Prtns Hles (55) Ampere secnd stands fr the unit f: (a) charge energy (56) The unit f electrmtive frce is: (a) Newtn (b) Ptential difference (d) Magnetic field (b) lectrns (d) Psitive and Negative ins (b) emf (d) pwer (b) Pascal Vlt (d) Ampere (57) The SI unit f temperature cefficient f resistivity is. (a) Ohm m (b) K 1 K (d) Ohm (58) The terminal ptential difference f a shrt-circuit battery f emf is equal t (a) (b) (59) Substances like germanium, Silicn have: (a) Psitive temperature cefficient Bth a and b (d) 0 (b) Negative temperature cefficient (d) Nne f these (60) Three resistances 5000, 500 and 50 Ohms are cnnected in series acrss 550 V mains. The current flwing thrugh them will be: (a) 1 A (b) 100 ma 10 ma (d) 1 ma BY: Prf. Muhammad Amin 4
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm SHOT QUSTIONS 13.1 A ptential difference is applied acrss the ends f a cpper wire. What is the effect n the drift velcity f free electrns by. (i) Increasing the ptential difference. (ii) Decreasing the length and the temperature f the wire Ans: (i) As V = d r V if d = cnstant. Abve relatin shws that by increasing the ptential difference V, will als increases. As, F q µ r F e s, F As increases, frce F n the free electrns will als increase Hence, the drift velcity will increase. V 1 (ii) As V = d r d= d µ (if V is cnstant) If the length d f the wire is decreased, lectric field intensity increases. S the drift velcity will increase. Decreasing temperature decreases the amplitude f vibratin f the atms. Then the chance f cllisin f free electrns with atms decreases. Hence the drift velcity increases 13. D bends in a wire affect its electrical resistance? xplain. Ans: As L A lectrical resistance f a wire depends upn its (i) nature (ii) length (iii) area f crss sectin Any bend in a wire d nt have any affect n the length, area f crss sectin r nature f wire. S the resistance will nt be affected. 13.3 What are the resistances f the resistrs given in the figures A and B? What is the tlerance f each? xplain what is meant by the tlerance? Ans:- First band = Brwn = 1 ND band = Green = 5 3 D band = ed = 00 4 TH band = Gld = 5 % S, = 1500 5% ST 1 Band = Yellw = 4 ND Band = White = 9 D 3 Band = Orange = 00 TH 4 Band = Silver = 10% S, = 49000 W± 10% Tlerance: Tlerance means the pssible variatin f a resistance frm the marked value. Fr example, a 1000resistance with a tlerance f ± 10% will have an actual resistance anywhere between 900 and 1100 BY: Prf. Muhammad Amin 5
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm 13.4 Why des the resistance f a cnductr rise with temperature? Ans: As the temperature f the cnductr rises, amplitude f the vibratin f atms f the lattice increases. As a result, cllisin f free electrn with themselves & with the vibrating atms increases and s resistance f the cnductr increases. 13.5. What are the difficulties in testing whether the filament f a lighted bulb beys Ohm s law? Ans: When current is passed thrugh the filament f a bulb, its temperature increases, s resistance increases. Hence filament f a bulb des nt bey hm s law, hm s law is nly beyed if the resistance is kept cnstant. 13.6 Is the filament resistance lwer r higher in a 500W, 0V light bulb than in a 100W, 0V bulb? Ans: Accrding t given data P1 = 500W V1 = 0V P = 100 V = 0 V We knw that V P= V = P (0) in first bulb 500 = =96.8Ω (500) (0) in secnd bulb 100 = =484Ω (100) Therefre resistance f 500W bulb is less than that f 100W bulb. 13.7 xplain why the terminal ptential difference f a battery decreases when the current drawn frm it is increased? Ans: We knw that terminal ptential is given as: Vt = Ir When current drawn I increases then factr Ir increases. Hence terminal P.D decreases. 13.9. What is Wheatstne bridge? Hw can it be used t determine an unknwn resistance? Ans: Wheatstne Bridge cnsist f fur resistances 1,,3 and4 cnnected in such a way t frm a mesh ABCDA. When the bridge is balanced electrically, n current flws thrugh the galvanmeter. 1 3 In this situatin. If ne f the resistance 4 = X is 4 unknwn resistance and the ther resistances 1,, and 3, are knwn, then 1 3 r X 3 S X can be fund. X 1 13.8 Describe a circuit which will give a cntinuusly varying ptential. Ans: Ptential divider circuit can prvide cntinuusly varying ptential. The circuit is shwn in Fig. vltage V is applied acrss A and B f the rhestat with the help f a battery. The current passing thrugh is given by V I=. The ptential difference between the pints BC is V current resis tan ce BC V I r BC V r VBC r V r VBC V BY: Prf. Muhammad Amin 6
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm This circuit can prvide a varying ptential difference frm 0 t V. As the sliding cntact C is mved twards the end B, The length and hence the resistr r f the prtin f wire decrease. As r V BC = V Hence, VBC decreases If C is mved twards the end A, r increases hence utput vltage increase ADDITIONAL SHOT QUSTIONS (1) Differentiate between MF and P.D? MF POTNTIAL DIFFNC It is a ptential difference acrss the surce when n current flws It is a ptential difference acrss the surce when sme current flws. emf is the cause. Ptential Difference is a effect f emf. It can never be zer. It may be zer It is given by the relatin. = V + Ir It is given by the relatin. V = Ir Vltmeter cnnected with surce measures emf with pen circuit. Vltmeter cnnected with surce measures Ptential Difference with clsed circuit. () Hw current flws thrugh a metallic cnductr. Ans: In the absence f electric field, the free electrns in cnductr are in randm mtin, which depends upn temperature. when electric field is set up in a cnductr by a surce which establishes cnstant ptential difference acrss the cnductr, the free electrns mdify their randm mtin in such a way that they drift slwly ppsite t field. Thus a net directed mtin f charges takes place alng the wire and a current begins t flw thrugh it. (3) What is series and parallel cmbinatins f resistrs. Ans: SIS COMBINATION esistances cnnected end t end are called series cmbinatin f resistance. i.e. PAALLL COMBINATION esistances cnnected side by side are called parallel cmbinatin f resistance. i.e. There is single path f current. There are mre than ne path f current. Current thrugh each resistance is same i.e. I 1 I I 3 I Sum f currents thrugh all resistances is equal t the net current f the circuit. I.e. I I I I Sum f ptential difference acrss each is equal t the ptential difference f the battery i.e. V V V V 1 3 quivalent resistance f series cmbinatin is... eq 1 3 quivalent resistance is greater than the maximum f all resistances cmbined in series i.e. eq 1, eq... eq max. 1 3 BY: Prf. Muhammad Amin 7 Ptential difference acrss each resistance is same as that f battery i.e. V V V V 1 3 quivalent resistance f parallel cmbinatin is 1 1 1 1... eq 1 3 quivalent resistance is less than the minimum f all resistance is less than the minimum f all resistances cmbined in parallel i.e.,... eq 1 eq eq max.
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm (4) What is difference between hmic and nn-hmic substances? Ans: OHMIC SUBSTANCS NON OHMIC SUBSTANCS Ohmic substances bey the Ohm s law. Nn hmic substances d nt bey hm s law. Graph between V and I fr hmic substances is straight line r linear. Graph between V and I fr nn hmic substances is nt straight line i.e. it is a curve. Slpe f graph remains same at all Slpe f the graph is nt same at all pints. xamples f hmic substances are pure metals. Graphs f hmic substances fr V vs I are as: pints. xamples f nn hmic substances are tungsten filament and semi cnductr dide. Graphs f nne hmic substances fr V vs I are as: (5) What is the temperature c-efficient f resistivity? Ans: The fractinal change in resistivity per Kelvin is knwn as temperature c-efficient f resistivity. Mathematically it can be written as ρ -ρ t α= ρt ρ Where is the resistivity f the material at 0 C and is the resistivity at t C, and t is the given change temperature. Unit:- The SI unit f temperature c-efficient f resistivity is K -1 (6) What is the difference between cnventinal current and electrnic current. Ans: Cnventinal current:- It is defined as that current which passes frm a pint at higher ptential t a pint at a lwer ptential as if it represents the mvement f psitive charges. lectrnic current:- The current due t mtin f negative charges (r electrns) that flws frm the negative terminal f the battery t the psitive terminal in the electrical circuit is called electrnic current. (7) State Kirchhff s 1 st and nd rule. Ans: Kirchhff s First ule It states that algebraic sum f currents meeting at a pint is zer. This is called Kirchhff s current law. Kirchhff s 1 st rule is als knwn as Kirchhff s pint rule. I = 0 Kirchhff s Secnd ule It is stated as: Algebraic Sum f vltage changes acrss a clsed circuit r lp must be equal t zer. Accrding t law f cnservatin f energy, the ttal change in energy f ur system is zer. Thus +1 Q - I1 Q - Q - I Q = 0 Or 1 I1 I = 0 (8) Name tw different effects f current. Ans: ffects f Current: Heating effect When current passes thrugh a cnductr due t resistance sme f electrical energy is cnverted int heat. BY: Prf. Muhammad Amin 8 ρ t
[CHAPT-13 CUNT LCTICITY] www.prfaminz.cm i.e H = I t where I = current, = resistance and t = time Magnetic effect It is intrinsic prperty that when a current passes thrugh a cnductr a magnetic field is prduced arund it. Chemical effect Certain liquids such as dilute sulphuric acid r cpper sulphate slutin cnducts ekctric current due t sme chemical reactins, this prcess is called electrlysis. (9) Hw can yu cmpare emf f tw cells with the help f a ptentimeter? Ans: Suppse 1 & are emf s f tw cells t be cmpared. Fr this purpse ptentimeter is balanced by cnnecting 1 & separately. Let l1 is the balancing length fr 1 & is the balancing length fr. These tw emf s will be cmpared by the fllwing frmula: l l 1 1 That is emf is prprtinal t balancing length in ptentimeter. (10) What is resistivity and hw it depend upn temperature. Ans: esistivity: It is defined as The resistance f a meter cube f a material. A L It unit is Dependence n Temperature: Within certain limits: (i) esistivity increases with increase f temperature f cnductr (ii) esistivity decreases with increase f temperature f semicnductr. (iii) esistivity remains cnstant with change f temperature f insulatr. (11) Write dwn the value f equivalent resistance fr three resistrs 1, and 3 when jined in (a) series, and (b) parallel. Ans: (a) Series: In case f series jining, the equivalent resistance will be e 1 3 (b) Parallel: In case f parallel jining, the equivalent resistance is fund as fllws: 1 1 1 1 e 1 3 1 3 13 1 e 1 3 1 3 e m 1 3 3 1 BY: Prf. Muhammad Amin 9