Physics Current electricity, Assignments of Physics

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>> Multiple Choice Questions (MCQs) \ DIRECTIONS: This section contains multiple choice questions. »>>> Each question has four choices (a), (b), (c) and (d) out of which only one is correct. 1. wn In the equation AB =C, A is the current density, C is the electric field, Then B is (a) resistivity (b) conductivity (c) potential difference (d) resistance A wire X has half the diameter and half the length of'a wire Y of similar material. The ratio of resistance of X to that of Y is (a) 8:1 (b) 4:1 (c) 2:1 (d) 1:1 The voltage Y and current / graphs for a conductor at two different temperatures 7, and 7, are shown in the figure. The relation between 7, and 7, is (a) 7, > 7, (b) 7, <7, (c) 7, =T, ] (d) 7, = rel The /-Y characteristics shown in figure represents (a) ohmic conductors I+ (b) non-ohmic conductors (c) insulators (d) superconductors If the resistance of a conductor is 5Q at 50° C & 7Q at 100° C, then mean temperature coefficient ofresistance (of material) is (a) 0.013/°C (b) 0.004/°C (c) 0.006/°C (d) 0.008/°C At what temperature will the resistance of a copper wire becomes three times its value at 0°C? (Temperature coefficient of resistance of copper is 4 x 1073/°C) (a) 550°C (b) 500°C (c) 450°C (da) 400°C e |’ 10. 11. 12. Current Electricity A potentiometer can measure emf ofa cell because [CBSE 2020] (a) the sensitivity of potentiometer is large. (b) nocurrent is drawn from the cell at balance. (c) no current flows in the wire of potentiometer at balance. (d) internal resistance of cell is neglected. Two resistors R, and R, of 4Q and 6 Q are connected in parallel across a battery. The ratio of power dissipated in them, P, : P, will be [CBSE 2020] (a) 4:9 (b) 3:2 (c) 9:4 (d) 2:3 A wire of radius r and another wire of radius 2r, both of same material and length are connected in series to each other. The combination is connected across a battery. The ratio of the heats produced in the two wires will be (a) 4.00 (b) 2.00 (c) 0.50 (d) 0.25 Emf ofa cellis (a) themaximum potential difference between the terminals ofa cell when no current is drawn from the cell. (b) the force required to push the electrons in the circuit. (c) the potential difference between the positive and negative terminal of a cell in a closed circuit. (d) less than terminal potential difference of the cell. An energy source will supply a constant current into the load if its internal resistance ts (a) very large as compared to the load resistance (b) equal to the resistance of the load (c) non-zero but less than the resistance of the load (d) zero To draw a maximum current from a combination of cells, how should the cells be grouped? (a) Parallel (b) Series (c) Mixed grouping (d) Depends upon the relative values of internal and external resistances 13. 14, 16. 17. 18. 19. 20. 21. A cell of internal resistance r is connected across an 22. external resistance nr. Then the ratio of the terminal voltage to the emf of the cell is @ + ow - © (d) n n+l n+l n If n cells each of emf ¢ and internal resistance r are connected in parallel, then the total emf and internal resistances will be (a) g-— = =(b) gar) (©) ang, o i i Under what condition will the strength ofcurrent in a wire of resistance R bethe same for connection is series and in parallel of n identical cells each of the internal resistance r? When (a) R=nr (b) R=rn (c) R=r (qd) Rox, r>0 The internal resistance ofa 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Q is (a) 0.50 (b) 0.8Q (c) 10Q (d) 0.2Q The figure below shows currents in a part of electric circuit. The current /is 1 amp n n-1l (d) né, ar (a) 1.7amp (b) 3.7amp (c) 1.3amp (d) lamp The resistances in (he two arms of ihe meter bridge are 522 1.3 amp and RQ, respectively. When the resistance R is shunted 25. with an equal resistance, the new balance point is at 1.6 /). The resistance “R’ is: —_{-—_—___, $Q RQ (a) 1002 (b) 15Q | y " | (c) 20Q o (d) 252 ans Too =7, 2° Sensitivity of potentiometer can be increased by (a) increasing the e.m.f ofthe cell (b) increasing the length of the potentiometer (c) decreasing the length of the potentiometer wire (d) None of these AB is a wire of potentiometer with the increase in value of resistance R, the shift in the balance point ./ will be (a) towards B fe - R (b) towards A (c) remains constant | (d) first towards B then back towards A In the figure in balanced condition of B wheatstone bridge (a) #isat higher potential. (b) Dis at higher potential. (c) Any of the two B or D can be at higher potential than other arbitrarily. (d) Band Dare at same potential. The resistance of an ammeter is 13 and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt-resistance is (a) 20 (b) 0.20 (c) 2kQ (d) 200 Consider a current carrying wire (current I) in the shape of acircle. (a) source of emf (b) electric field produced by charges accumulated on the surface of wire (c) the charges just behind a given segment of wire which push them just the right way by repulsion (d) the charges ahead Two batteries of emf €, and ¢,(€, > €,) and internal resistances r, and r, respectively are connected in parallel as shown in figure. (a) The equivalent emf €, 4 of the two cells is between ¢ and E>, i.€., 6, < bag <6, (b) The equivalent emfe, . is smaller than € (c) The Bog is given by E_q = 8 + &) always (d) Gog is independent of internal resistances r, andr, ! l By A resistance R is to be measured using a meter bridge, student chooses the standard resistance S to be 1000. He finds the null point at /, = 2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way? (a) He should measure I, more accurately (b) He should change 5 to 100002 and repeat the experiment (c) He should change S to 3Q and repeat the experiment (d) He should given up hope of a more accurate measurement with a meter bridge Two cells of emfs approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm. (a) The battery that runs the potentiometer should have voltage of 8V (b) The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V (c) The first portion of 50 cm of wire itself should have a potential drop of 10 V (d) Potentiometer is usually used for comparing resistances and not voltages A metal rod of length 10 cm and a rectangular cross-section ] , of lem x 5 cm is connected to a battery across opposite faces. The resistance will be (a) maximum when the battery is connected across 1 cm = ul cm faces 2 45. 46. 47. 48. 49. 50. 51. 53. 54. In the circuit shown in Fig, the current in 4 Q resistance is 1.2 A. What is the potential difference between B and C? (a) 3.6 volt Ly 4 (b) 6.3 volt i (c) 1.8 volt (d) 2.4 volt iL Kirchhoff’s first and second laws for electrical circuits are consequences of (a) conservation of electric charge and energy respectively (b) conservation of electric charge (c) conservation of energy and electric charge respectively (d) conservation of energy Emfofa cell is (a) the maximum potential difference between the terminals of a cell when no current is drawn from the cell, (b) the force required to push the electrons in the circuit. (c) the potential difference between the positive and negative terminal of a cell ina closed circuit. (d) less than terminal potential difference of the cell. When potential difference is applied across an electrolyte, then Ohm’s law is obeyed at (a) zero potential (b) very low potential (c) negative potential (d) high potential To draw a maximum current from a combination of cells, how should the cells be grouped? (a) Parallel (b) Series (c) Mixed grouping (d) Depends upon the relative values of internal and external resistances. A cell of internal resistance r is connected to an external resistance R. The current will be maximum in R, if (a) R=r (b) Rr (d) R=r/2 Under what condition will the strength of current in a wire of resistance R be the same for connection is series and in parallel ofn identical cells each of the internal resistance r? When (a) R=nr (b) R=rMm (c) R=r (d) R>oaw,r>0 A capacitor is connected to a cell of emf E having some internal resistance r. The potential difference across the (a) cellis E (d) capacitor is» Case/Passage Based Questions \\\\ ——— DIRECTIONS : Study the given Case/Passage and answer the following questions. (d) (d) (d) >>>? Case/Passage-I The motion of free electrons in a conductor are continuous and random. They collide with positive metal ions and change direction during each collision. So thermal velocities are randomly distributed and average velocity is zero. - When a potential difference is applied across the ends of a conductor, electrons are drifted towards the positive terminal of the field, this velocity is called drift velocity (v,). eEr __ Vqg=-— 7 m neaA 72. IfN,e, tand mare representing electron density, charge, relaxation time and mass ofan electron respectively, then the resistance of wire of length ¢ and cross-sectional area A is given by mf 2mtA (a) Nez At (b) Ne? £ Ne? tA Ne? A ©) “ame Q) omtl 73. When acurrent I is set up in a wire of radius r, the drift velocity is vj. If the same current is set up through a wire of radius 2 r, the drift velocity will be (a) 4V4 (b) 2, (c) v,/2 (d) v,/4 74. A straight conductor of uniform cross-section carries a current I. If s is the specific charge of an electron, the momentum ofall the free electrons per unit length of the conductor, due to their drift velocity only is (a) Is (b) JI/s (c) I/s (d) (l/s)? 75. Theresistance ofa wire at room temperature 30°C is found to be 10 Q. Now to increase the resistance by 10%, the temperature of the wire must be [The temperature coefficient of resistance of the material of the wire is 0.002 per °C] (a) 36°C (b) 83°C (c) 63°C (d) 33°C 76. Thenumber of free electrons per 100 mm of ordinary copper wire is 2 x 102!, Average drift speed of electrons is 0.25 mm/s. The current flowing is (a) SA (c) 8A (b) 80A (d) O8A Case/Passage-II Heating Effect of Current: The electric energy consumed in a circuit is defined as the total work done in maintaining the current in an electric circuit for a given time. Electric energy = Vit= Pt =P Ri= V>1/R The 8.1. unit of electric energy is joule (denoted by J) where | joule= 1 watt x 1 second = 1 volt x 1 ampere < | sec. In household circuits the electrical appliances are connected in parallel and the electrical energy consumed is measured in kWh 77 ~+Anelectric fan and a heater are marked as 100 W, 220 V and 1000 W, 220 V respectively. The resistance of heater is (a) equal to that of fan (b) lesser than that of fan (c) greater than that of fan (d) zero ol. In a potentiometer experiment, the balancing with a cell is at length 240 cm. On shunting the cell with a resistance of 2 Q, the balancing length becomes 120 cm. The internal resistance of the cell is (az) 22 =) 49 (©) 05 (d) 12 Case/Passage-V It an instrument based on wheatstone bridge. Principle:— The fall of potential across any portion of the wire is directly proportional to the length of that portion provided the wire of uniform cross-section and a constant current is flowing through it. Theory : If A be the area of cross-section of the wire, P be the specific resistance of the material of the wire. V be the potential difference across the portion of the wire whose length is ¢ and resistance R. I be the current flowing through the wire then by Ohm’s law, Or, fp _ (Ip pe V=IR=I A (<2) a V « € ifA and] are constants V a = k = Potential gradient or fall of potential /length of the wire. 92. 93. 94. 95. = | If specific resistance of a potentiometer wire is 10-7Qm current flowing through it, is 0.1 amp and cross sectional area of wire is 10~° m2, then potential gradient will be (a) 10°? volt/m (b) 10-*volt/m (c) 10-6 volt/m (d) 10-8 volt/m A cell when balanced with potentiometer gave a balance length of 50 cm. 4.5 Q external resistance is introduced in the circuit, now it is balanced on 45 cm. The internal resistance of cell is (a) 0.25Q (b) 0502 (c) 10Q (dd 150 A potentiometer consists of a wire of length 4m and resistance 10Q. It is connected toa cell of e.m.f. 3V. The potential gradient of wire is (a) 5Vim (b) 2V/in~ (c) 5V/m~— (d) 10V/m In an experiment to measure the internal resistance of a cell, by a potentiometer, it is found that the balance point is at a length of 2 m, when the cell is shunted by a 5 Q resistance and is at a length of 3 m when the cell is shunted bya 10 Q resistance. The internal resistance of the cell is (a2) 152 (b) 10Q (© bQ @ 12 96. >> Assertion & Reason \\\—— 125 cm of potentiometer wire balances the emf. of a cell and 100 cm of the wire is required for balance, ifthe poles of the cell are joined by a 202 resitor. Then the internal resistance of the cell is (a) 0.252 (b) 05Q (c) 0.75Q 1.25Q (d) >>>? DIRECTIONS : Each of these questions contains an assertion followed by reason. Read them carefully and answer the question on the basis of following options. You have to select the one that best describes the two statements. (a) (b) (c) (d) 97. 98. 99, 100. 101. 102. 103. 104. fboth Assertion and Reason are correct and the Reason is the correct explanation of the Assertion. if both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion. fthe Assertion is correct but Reason is incorrect. fthe Assertion is incorrect but the Reason is correct. Assertion : switch is on. Reason : The drift velocity of electrons in a metallic wire is very high. Assertion: For a conductor resistivity increases with increase in temperature. itl The electric bulbs glows immediately when Reason: Since P = , when temperature increases the net random motion of free electrons increases and vibration of ions increases which decreases T. Assertion : The current density J at any point in ohmic resistor is in direction of electric field E at that point. Reason : A point charge when released from rest in a region having only electrostatic field always moves along electric lines of force. Assertion : Free electrons always keep on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it. Reason : The average velocity of free electron is zero. Assertion : Drift speed v , is the average speed between two successive collisions. Reason : [f Af is the average distance moved between two collisions and Af is the corresponding time, then Af vg = lim —., Aroo At Assertion : Fuse wire must have high resistance and low melting point. Reason : Fuse is used for voltage stablisation only. Assertion : The (100w, 220 v) bulb glow with more brightness than, (50w, 220v) bulb. Reason : |00w bulb has more resistance than 5Ow bulb. Assertion : When current through a bulb decreases by 0.5%, the glow of bulb decreases by 1%. Reason : Glow (Power) which 1s directly proportional to square of current. 105. 106. 107. 108. 109. 110. 111. 112. >> Match the Following Assertion : Long distance power transmission is done at high voltage. Reason : At high voltage supply power losses are less. Assertion; A larger dry cell has higher emf. Reason : The emf ofa dry cell is proportional to its size. Assertion : In a simple battery circuit, the point of the lowest potential is negative terminal of the battery. Reason : The current flows towards the point of the higher potential, as it does in such a circuit from the negative to the positive terminal. Assertion : Kirchoff’s junction rule can be applied to a Junction of several lines or a point in a line. Reason : When steady current is flowing, there is no accumulation of charges at any junction or at any point in a line. Assertion : A potentiometer of longer length is used for accurate measurement. Reason : The potential gradient for a potentiometer of longer length with a given source of e.m.f becomes small. Assertion : Kirchoff’s junction rule follows from conservation of charge. Reason : Kirchoff’s loop rule follows from conservation of momentum. Assertion : A potentiometer of longer length is used for accurate measurment. Reason : The potential gradient for a potentiometer of longer length with a given source of e.m.f becomes small. Assertion : Bending a wire does not effect electrical resistance. Reason : Resistance of wire is proportional to resistivity of material. DIRECTIONS : Each question contains statements given in two columns which have to be matched. Statements (A, B, C, D) in column-I have to be matched with statements (I, 2, 3, 4) in column-ll. 113. Match the Column I and Column II. Column I Column II Smaller the resistance (1) If the same voltage is preater the current applied and resistance are in series If the same current is passed (A) (B) Greater or smaller the (2) resistance the current is same Greater the resistance (3) smaller the power When resistances are connected in series Greater the resistance (4) When resistances are greater the power connected in parallel (A) > (3); (B) > (1); (C) > 2); (D) 9 4) (A) > (1); (B) > (3); ©) (2): (D9 (4) (A)> (2); (B) > (1); (C)> 4): (D)> GB) (A)> (4); (B) > (3); (CQ) (1): (D)> 2) (©) (D) (a) (b) (c) (d) 114. >> Fill in the Blanks \\\ —— Match the entries of Column I[ with their correct mathematica! expressions in Column II Column! Column IT (A) Balancedcondition (1) 4.4 of wheatstone bridge ROR, R l (B) Comparisonofemfof (2) = wa i two cells. (C) Determination of (3) Le 4 . ; BE, L internal resistance of , a cell (D) Determination of (4) -= unknown resistance by meter bridge (a) (A)—>(4):(B)>(): C (3); (D) 9 (1) (b) (A) (1): (B)->(3); C3 (4): (D) 3 (2) (c) (A)—>(3):(B)> (4); C3 (2): (D) 9 (1) (d) (A)—>(4):(B)—> (3); C> (2): (D) 9 (1) »>>> DIRECTIONS : Complete the following statements with an appropriate word / term to be filled in the blank space(s). 115. 116 117. 118. 119. A \—$§ : : DAY The current in the 1Q resistor 40 shown in the circuit is Ay Lanna | 1 6V WV 40 A primary cell has an e.m_f. of 6. volt, when short-circuited it gives a current of 3 ampere. The internal resistance of the cells is ohm. A 5—ampere fuse wire can withstand a maximum power of 1 watt in the circuit. The resistance of the fuse wire is ohm. A heater of 220 V heats a volume of water in 5 minutes. The same heater when connected to 110 V heats the same volume of water in minutes. A battery of 10 V and internal resistance 0.592 is connected across a variable resistance R. The value of R for which the power delivered is maximum is equal to Q. >>>> DIRECTIONS : Read the following statements and write your answer as true or false. 120. 121. 122. 123. Voltmeter is connected in parallel with the circuit. Resistance ofa voltmeter is very small. The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased. On increasing temperature, conductivity of metallic wire inecreases. 17. 18. 19. 20. 21. 22. 23. 24. 25. From formula. s—-Ir=V=IR 2.1—0.2r=0.2 x 10 0.1 2.1-0.2r=2 or 0.2r=0.1 > T= Oy 7952 (a) According to Kirchhoff’s first law Atjunction A, i;2=2+2=4A At junction B, isp=igot lipo =4-1>3A 26. Atjunction C, i=ip--1.3=3-13=1.7A (b) This is a balanced wheatstone bridge condition, 2 = ang 2 = 1 nis R 100-4, R/2 100-1.6¢, (b) 21. (a) Due to increases in resistance R the current through the wire will decrease and hence the potential gradient also decreases, which results in increase in balancing length. So. J will shift towards P. (da) Imbalance condition, since no current Nows through the galvanometer therefore B and D are at the same 49° potential. (a) We know I G ——_ = |+ — Is S 750 13 — = |4+ — 100 Ss 29, S > 20 (b) As we know, electric current per unit area I/A, is called current density ji.e., j= - The SI units of the current density are A/m?. The current density is also directed along E and 1s also a vector and the relationship is j=OE Current density changes due to electric field produced by 30. charges accumulated on the surface of wire. (a) As we know the equivalent emf (¢, 4) in the parallel combination £1, +€,f, E.= rere, So according to formula the equivalent emf ¢, 4 of the two cells in parallel combination is between €, and €,. Thus (€,<£,,< &). (c) Adjusting the blance point near the middle of the bridge, 1.¢.. when /, is close to 50 cm. requires a suitable choice of S, R is unknown resistance : R R/ = L SUINEy g R(100-/) n-sf29] 97.1 So, here, R : S =2.9 : 97.1 implies that the S is nearly 33 times to that of R. In orded to make this ratio 1 : 1 it ts 1. . necessary to reduce the value of S nearly 3 times 1.€., ~ nearly 3.Q. (b) The potential drop across wires of potentiometer should be more than emfs of primary cells. Here, values of emfs of two cells are given as 5V and 10V, so the potential drop along the potentiometer wire must be more than LOV. So battery should be of 15V and about 4V potential is droped by using variable resistance. / (a) Aswe known that the resistance of wire is R= Pa For maximum value of R, / must be higher and A should be lower and itis possible only when the battery is connected ; l across area of cross section = lem~x (- cm. (a) We know that the relationship between current and drift speed 1s I= ne Av, Where, I is the current and V, is the drift velocity. So, Io V, Hence, only drift velocity determines the current in a conductor. (c) I= R+R,+R3 Pot. difference across Se a second cell = V=e—-IR> =() . R+ Ry + R> R+R, +R,-2R> =(0 R+R,-R,=0 «R= (c) Applying Kirchhoff’s law in BCDEFAB we get, =F i| l= V 3R Vv Cc LetAbeatOV.Then {7-4 > potential at G is V. Applying Krichhoff’s q! law for AFED, we get pit ANN C 0+V+IR=Vp 2V te Ve ch, a, eo. 3R 3 & 4V V .. potential different across capacitor = 3 Ve 7 32. 33. 34. 39. 41. 42. 43. 44. 46. 47. 48. = (a) Potential gradient of wire = ~ = [2.1 A where ¢ & A are the length and cross-section of wire V 4x10” | *0.5 = 25mV / meter € 8x10 50 (a) (b) Motion of conduction electrons due to random collisions has no preffered direction and average to zero. Drift velocity is caused due to motion of conduction electrons due to applied electric field E. (d) 35. (b) 36. (a) 37. (d) (a) 40. (b) (b) These materials exhibit a very weak dependence of resistivity on temperature. Their resistance values would be changed very little with temperature as shown in figure. 38. (a) Resistivity p{u(em)——> > i> Hence these materials are widely used as heating element. (d) Resistivity depends on various other factors like temp. (c) Nocurrent flows through the resistor R as P and QO are at same potential. Hence current drawn from battery will remain same on closing the switch. (a) As the ring has no resistance, the three resistances of 3R each are in parallel. I I l I 1 = + + =—=>R=R R’ 3R 3R 3R R .. between point A and B equivalent resistance =R+R=2R (a) The potential difference across 4Q resistance is given by V=41,=4 1.2=4.8 volt => So, the potential across 8Q resistance is also 4.8 volt. . V_ 48 Current 1, =—= ra 0.6 amp Current in 2Q resistance 1=1, +1, “ 1=1.2+0.6=1.8 amp Potential difference across 2Q resistance Vacs 1.8 *2= 3.6 volts (a) Kirchhoff’ s first law deals with conservation of electrical charge & the second law deals with conservation of electrical energy. (a) Because of internal resistance of cell. (d) 49. (d) 50. (a) 51. (c) (b) In the given case cell is in open circuit (i = 0) so voltage across the cell is equal to its e.m.f. (a) 54. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 71. TS. 74. (a) In the parallel combination, ESE vege Veg A 1% Tn ! 1 1 1 er a apie leg WO ly (Sf €)= 6 = =...56, =eandr, =1rj=1, =... 7) Seg & & & § =—+—+...t-=7- (i) Meg OF r r Ee Ll. 1 i & l on ty of t me ¢ Vege vn ...(il) From (i) and (ii) é 2 x guage & a leg “ ee (b) AsR co V2/P or Rec 1/P, so resistance of heater is less than that of fan. 1 qd) He 7 [as V = constant in parallel connection] 5 1) a T T r=0.05Q>H= i*rt=(307 * 0.05 x 20=900J (@d) As Rx © Rif RaoH2s 1 Power (b) Since, the voltage is same for the two combinations, l therefore H oc R . Hence, the combination of 39 bulbs will glow more. (c) Ifa heater boils m kg water in time t, and another heater boils the same water in t,, then both connected in series will boil the same water in time t,=t, + t, and ifin t,t : parallel t, = —12— [Use time taken Resistance] Pt) +t, 210x5x60 (ce) H=Pxt=2—72*™ = 15000 cal. (d) (b) The deflection in galvanometer will not be changed due to interchange of cells and the galvanometer. (a) In meter bridge experiment, it is assumed that the resistance of the £ shaped plate is negligible, but actually it is not so. The error created due to this ts called end error. To remove this the resistance box and the unknown resistance must be interchanged and then the mean reading must be taken. (b) Potentiometer is based on zero deflection method. (b) 67. (b) 68. (b) 69. (a) 70. (c) (c) 72. (a) d) I=nAev,orv,% l/nr* (c) 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. (c) Drift speed is the average speed between two successive collisions. (c) (c) (a) Glow= Power (P)=?R A =2[F)=2405=1% P ] (a) Power loss= i?R= (4) R [P= Transmitted power] (d) Thee.m.f ofa dry cell is dependent upon the electrode potential of cathode and anode which in turn is dependent upon the reaction involved as well as concentration of the electrolyte. It has nothing to do with size of the cell. (c) Positive terminal of a battery is point of highest potential and current flows from highest to lowest potential i.e. from +ve to—ve potential. (a) | Potential gradient (a) Sensitivity x x (Length of wire) (c) Kirchoff's loop rule follows from conservation of energy. l (a) Sensitivity * Potential gradient x Length of wire. 7 (a) Resistance wire R = PT , where p is resistivity of material which does not depend on the geometry of wire. Since when wire is bent resistivity, length and area of cross- section do not change, therefore resistance of wire also remain same. () A>(2);B>(1);C> (4); D> (3) b) A(1);B-(3);C >); D>(2) (2A) Two 4Q resistors are in parallel combination. Their equivalent resistance _ 4x4 16 _ 4+4 8 202 116. 117. 118. 119. 120. 121. 122. 123. 4Q 4Q AAA | 10 év “. Total resistance ofthe network = 2+ 1=30 . Current through |Q resistor = ~ =2A (2Q) Short circuit current E 6 is0 = SD 3 =- DS r= 20 r r (0.04Q) R= _ A = 0.040 j 25 Vt R aa V2 = constant. ic ty = V7 ty => 2202 x 5 = 11077, “f= 20min. (20 min) W = Power x time = R is the same. (0.502) Power is maximum when r= R, R=r=0.5Q. (True) Voltmeter is a galvanometer with high resistance. It measures potential drop across any part of an electrical circuit. It is connected in parallel so that it does not draw any current itself (due to high resistance) and does not affect net resistance of the circuit. (False) (True) On increasing temperature of wire the kinetic energy of free electrons increase and so they collide more rapidly with each other and hence their drift velocity decreases. (False) Also when temperature increases, resistivity increases and resislivily is inversely proporuional to conductivity of material.