**NEET AIPMT Physics Chapter Wise Solutions – Current Electricity**

NEET AIPMT Physics Chapter Wise SolutionsChemistryBiology

**1. Two metal wires of identical dimensions are connected in series. If σ _{1} and σ_{2} are the conductivities of the metal wires respectively, the effective conductivity of the combination is (AIPMT 2015)**

**2. A circuit contains an ammeter, a battery of 30 V and a resistance 40.8 ohm all connected in series. If the ammeter has a coil of resistance 480 ohm and a shunt of 20 ohm, the reading in the ammeter will be (AIPMT 2015)**

(a) 2 A

(b) 1 A

(c) 0.5 A

(d) 0.25 A

**3. A potentiometer wire of length L and a resistance r are connected in series with a battery of e.m.f. E _{0} and a resistance r_{1}. An unknown e.m.f. E is balanced at a length / of the potentiometer wire. The e.m.f. E will be given by (AIPMT 2015)**

**4. A, B and C are voltmeters of resistance R, 1.5R and 3R respectively as shown in the figure. When some potential difference is applied between X and Y, the voltmeter readings are V _{a } V_{b } and V_{c} respectively. Then (AIPMT 2015, Cancelled)**

**5. Across a metallic conductor of non-uniform cross section a constant potential difference is applied. The quantity which remains constant along the conductor is (AIPMT 2015, Cancelled)**

(a) drift velocity

(b) electric field

(c) current density

(d) current

**6. A potentiometer wire has length 4 m and resistance 8 Ω. The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2 V, so as to get a potential gradient 1 mV per cm on the wire is (AIPMT 2015, Cancelled)**

(a) 44 Ω

(b) 48 Ω

(c) 32 Ω

(d) 40 Ω

**7. Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 Ω. The power loss in the wire is (AIPMT 2014)**

(a) 19.2 W

(b) 19.2 kW

(c) 19.2 J

(d) 12.2 kW

**8. The resistances in the two arms of the meter bridge are 5 Ω and R Ω respectively.When the resistance R is shunted with an tjqual resistance, the new balance point is at 1.6I _{1}. The resistance R is
**

(a) 10 Ω

(b) 15 Ω

(c) 20 Ω

(d) 25 Ω

**9. A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and a negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance R, connected across the given cell, has values of (AIPMT 2014)**

(i) infinity

(ii) 9.5 Ω

the balancing lengths on the potentiometer wire are found to be 3 m and 2.85 m, respectively. The value of internal resistance of the cell is

(a) 0.25 Ω

(b) 0.95 Ω

(c) 0.5 Ω

(d) 0.75 Ω

**10. The resistances of the four arms P, Q, R and S in a Wheatstone’s bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be (NEET 2013)**

(a) 0.1 A

(b) 2.0 A

(c) 1.0 A

(d) 0.2 A

**11. The internal resistance ofa 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is (NEET 2013)**

(a) 0.8 Ω

(b) 1.0 Ω

(c) 0.2 Ω

(d) 0.5 Ω

**12. A wire of resistance 4 Ω is stretched to twice its original length. The resistance of stretched wire would be (NEET 2013)**

(a) 8 Ω

(b) 16 Ω

(c) 2 Ω

(d) 4 Ω

**13. Two rods are joined end to end, as shown. Both have a cross-sectional area of 0.01 cm ^{2}. Each is 1 meter long. One rod is of copper with a resistivity of 1.7 × 10^{-6} ohm-centimeter, the other is of iron with a resistivity of 10^{5} ohm-centimeter. How much voltage is required to produce a current of 1 ampere in the rods? (Karnataka NEET 2013)**

(a) 0.00145 V

(b) 0.0145 V

(c) 1.7 × 10

^{-6 }V

(d) 0.117 V

**14. A 12 cm wire is given a A shape of a right angled triangle ABC having 3 cm sides 3 cm, 4 cm and 5 cm as shown in the B figure. The resistance between two ends (AB, BC, CA) of the respective sides are measured one by one by a multi-meter. The resistances will be in the ratio (Karnataka NEET 2013)
**

(a) 9 : 16 : 25

(b) 27 : 32: 35

(c) 21 : 24 : 25

(d) 3 :4 : 5

**15. Ten identical cells connected in series are needed to heat a wire of length one meter and radius r by 10°C in time How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time ” t ‘? (Karnataka NEET 2013)**

(a)20

(b)30

(c)40

(d)10

**16. In the circuit shown the cells A and B have negligible resistances. For V _{a} = 12 V, R_{1} = 500 Ω and R= 100 Ω the galvanometer (G) shows no deflection. The value of VB is (Prelims 2012)**

(a) 4V

(b) 2 V

(c) 12 V

(d) 6V

**17. A ring is made of a wire having a resistance R0 = 12 Ω. Find the points A and B, as shown in the figure, at which a current carrying conductor should be connected so’that the resistance R of the sub circuit between these points is equal to 8/3 Ω
**

**18. If voltage across a bulb rated 220 volt-100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is (Prelims 2012)**

(a) 20 %

(b) 2.5 %

(c) 5 %

(d) 10 %

**19. A cell having an emf e and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by (Mains 2012 )
**

**20. The power dissipated in the circuit shown in the figure is 30 watts. The value of R is (Mains 2012)
**

(a) 20 Ω

(b) 15 Ω

(c) 10 Ω

(d) 30 Ω

**21. A current of 2 A flows through a 2 Ω resistor when connected across a battery. The same battery supplies a current of 0.5 A when connected across a 9 Ω resistor. The internal resistance of the battery is (Prelims 2011)**

(a) 0.5 Ω

(b) 1/3 Ω

(c) 1/4 Ω

(d) 1 Ω

**22. If power dissipated in the 9 Ω resistor in the circuit shown is 36 watt, the potential difference across the 2 Ω resistor is (Prelims 2011)
**

(a) 4 volt

(b) 8 volt

(c) 10 volt

(d) 2 volt

**23. In the circuit shown in the figure, if the potential at point A is taken to be zero, the potential at point B is (mains 2011)
**

(a) + 1V

(b) – IV

(c) +2V

(d) -2 V

**24. A potentiometer circuit is set up as shown. The potential gradient, across the potentiometer wire, is k volt/cm and the ammeter, present in the circuit, reads 1.0 A when two way key is switched off. The balance points, when the key between the terminals (i) 1 and 2 (ii) 1 and 3, is plugged in, are found to be at lengths l _{1} cm and l_{2} cm respectively. The magnitudes, of the resistors R and X, in ohms, are then, equal, respectively, to (Prelims 2010)**

**25. Consider the following two statements. (Prelims 2010)**

(A) Kirch hoffs junction law follows from the conservation of charge.

(B) Kirch hoff’s loop law follows from the conservation of energy.

Which of the following is correct?

(a) Both (A) and (B) are wrong

(b) (A) is correct and (B) is wrong

(c) (A) is wrong and (B) is correct

(d) Both (A) and (B) are correct

**26. See the electrical circuit shown in this figure. Which of the following equations is a correct equation for it? (Prelims 2009)
**

**27. A wire of resistance 12 ohms per meter is bent to form a complete circle of radius 10 cm. The resistance between its two diametrically opposite points, A and B as shown in the figure is (Prelims 2009)
**

(a) 3 Ω

(b) 671 Ω

(c) 6 Ω

(d) 0.67 π Ω

**28. A student measures the terminal potential difference (V) of a cell (of emf e and internal resistance r) as a function of the current (7) flowing through it. The slope, and intercept, of the graph between V and I, then, respectively, equal (Prelims 2009)**

(a) – r and E

(b) r and – E

(c) – E and r

(d) E and – r

**29. The mean free path of electrons in a metal is 4 × 10 ^{-8} m. The electric field which can give on an average 2 eV energy to an electron in the-metal will be in units V/m (Prelims 2009)**

(a) 5 x 10

^{-11}

(b) 8 x 10

^{-11}

(c) 5 x 10

^{7}

(d) 8 x 10

^{7}

**30. In the circuit shown, the current through the 4 Ω resistor is 1 amp when the points P and M are connected to a d.c. voltage source. The potential diff erence between the points M and N is (Prelims 2008)
**

(a) 0.5 volt

(b) 3.2 volt

(c) 1.5 volt

(d) 1.0 volt

**31. A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively (Prelims 2008)**

(a) both remain the same

(b) 1.1 times, 1.1 times

(c) 1.2 times, 1.1 times

(d) 1.21 times, same

**32. A cell can be balanced against 110 cm and 100 cm of potentiometer wire, respectively with and without being short circuited through a resistance of 10 Ω. Its internal resistance is (Prelims 2008)**

(a) 2.0 ohm

(b) zero

(c) 1.0 ohm

(d) 0.5 ohm

**33. An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20°C ? The temperature of boiling water is 100°C (Prelims 2008 )**

(a) 12.6 min

(b) 4.2 min

(c) 6.3 min

(d) 8.4 min

**34. A current of 3 amp. flows through the 2 Ω resistor shown in the circuit. The power dissipated in the 5 Ω resistor is JQ (Prelims 2008)
**

(a) 1 watt

(b) 5 watt

(c) 4 watt

(d) 2 watt

**35. Three resistances P, Q, R each of 2 Ω and an unknown resistance S form the four arms of a Wheatstone bridge circuit. When a resistance of 6 Ω is connected in parallel to S the bridge gets balanced. What is the value of SI (2007)**

(a) 3 Ω

(b) 6 Ω

(c) 1 Ω

(d) 2 Ω.

**36. The total power dissipated in watt in the circuit shown here is (2007)
**

(a) 40

(b) 54

(c) 4

(d) 16.

**37. In the circuit shown, if a conducting wire is connected between points A and B, the current in this wire will (2006)
**

(a) flow from B to A

(b) flow from A to B

(c) flow in the direction which will be decided by the value of V

(d) be zero.

**38. Kirchhoffs first and second laws of electrical circuits are consequences of (2006)**

(a) conservation of energy and electric charge respectively

(b) conservation of energy

(c) conservation of electric charge and energy respectively

(d) conservation of electric charge.

**39. Two cells, having the same e.m.f. are connected in series through an external resistance R. Cells have internal resistances r, and r2 (r _{1} > r_{2}) respectively. When the circuit is closed, the potential difference across the first cell is zero. **

**The value of R is (2006)**

**40. Power dissipated across the 8 Ω resistor in the circuit shown here is 2 watt. The power dissipated in watt units across the 3 Ω resistor is (2006)
**

(a) 3.0

(b) 2.0

(e) 1.0

(d) 0.5

**41. Two batteries, one of emf 18 volts and internal resistance 2 Ω and the other of emf 12 volts and internal resistance 1 Ω, are connected as shown. The voltmeter V will record a reading of (2005)
**

(a) 30 voIt

(b) 18 voIt

(c) 15 voIt

(d) 14 volt.

**42. When a wire of uniform cross-section a, length ¡ and resistance R is bent into a complete circle, resistance between any two of diametrically opposite points will be (2005)**

(a) R/4

(b) 4R

(c) R/8

(d) R/2.

**43. For the network shown in the figure the value of the current i is (2005)
**

**44. A 5-ampere fuse wire can withstand a maximum power of 1 watt in the circuit. The resistance of the fuse wire is (2005)**

(a) 0.04 ohm

(b) 0.2 ohm

(c) 5 ohm

(d) 0.4 ohm.

**45. The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then (2004)**

(a) The resistance will be doubled and the specific resistance will be halved.

(b) ‘The resistance will be halved and the specific resistance will remain unchanged.

(e) The resistance will be halved and the specific resistance will be doubled.

(d) The resistance and the specific resistance, will both remain unchanged.

**46. Resistance n, each of r ohm, when connected in parallel give an equivalent resistance of R ohm. If these resistances were connected in series, the combination would have a resistance in ohms, equal to (2004)**

(a) n^{2 }R

(b) R/n^{2}

(c) R/n

(d) nR

**47. Five equal resistances each of resistance R are connected as shown in the figure. A battery of V volts is connected between A and B. The current flowing in AFCEB will be (2004)
**

**48. A 6 volt battery is connected to the terminals of a three metre long wire of uniform thickness and resistance of 100 ohm. The difference of potential between two points on the wire separated by a distance of 50 cm will b®f (2004)**

(a) 2 volt

(b) 3 volt

(c) 1 volt

(d) 1.5 volt

**49. When three identical bulbs of 60 watt, 200 volt rating are connected in series to a 200 volt supply, the power drawn by them will be (2004)**

(a) 60 watt

(b) 180 watt

(c) 10 watt

(d) 20 watt

**50. In India electricity is supplied for domestic use at 220V. It is supplied at 110 V in USA. If the resistance of a 60 W bulb for use in India is R, the resistance of a 60 W bulb for use in USA will be (2004)**

(a) R

(b) 2R

(c) R/4

(d) R/2

**51. In a Wheatstone’s bridge all the four arms have equal resistance R. If the resistance of the galvanometer arm is also R, the equivalent resistance of the combination as seen by the battery is (2003)**

(a) R/4

(b) R/2

(c) R

(d) 2R

**52. Two 220 volt, 100 watt bulbs are connected first in series and then in parallel. Each time the combination is connected to a 220 volt a.c. supply line. The power drawn by the combination in each case respectively will be (2003)**

(a) 50 watt, 100 watt

(b) 100 watt, 50 watt

(c) 200 watt, 150 watt

(d) 50 watt, 200 watt

**53. An electric kettle has two heating coils. When one of the coils is connected to an a.c. source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be (2003)**

(a) 8 minutes

(b) 4 minutes

(c) 25 minutes

(d) 15 minutes

**54. Fuse wire is a wire of (2003)**

(a) high resistance and high melting point

(b) high resistance and low melting point

(c) low resistance and low melting point

(d) low resistance and high melting point

**55. For a cell terminal potential difference is 2.2V when circuit is open and reduces to 1.8 V when cell is connected to a resistance of R = 5 Ω. Determine internal resistance of cell (r) (2002)
**

**56. Specific resistance of a conductor increases with (2002)**

(a) increase in temperature

(b) increase in cross-section area

(c) increase in cross-section and decrease in length

(d) decrease in cross-section area.

**57. Copper and silicon is cooled from 300 K to 60 K, the specific resistance (2001)**

(a) decrease in copper but increase in silicon

(b) increase in copper but decrease in silicon

(c) increase in both

(d) decrease in both.

**58. The resistance of each arm of the Wheatstone’s bridge is 10 ohm. A resistance of 10 ohm is connected in series with a galvanometer then the equivalent resistance across the battery will be (2001)**

(a) 10 ohm

(b) 15 ohm

(c) 20 ohm

(d) 40 ohm.

**59. If specific resistance of a potentiometer wire is 10 ^{-7} Ωm and current flow through it is 0.1 amp. cross sectional area of wire is 10^{-6}m^{2} then potential gradient will be (2001)**

(a) 10

^{-2}volt/m

(b) 10

^{-4}volt/m

(c) 10

^{-6}volt/m

(d) 10

^{-8}volt/m.

**60. The net resistance of the circuit between A and B is (2000)
**

**61. A car battery of emf 12 V and internal resistance 5 x 10 ^{-2} Ω, receives a current of 60 amp, from external source, then terminal potential difference of battery is (2000)**

(a) 12 V

(b) 9 V

(c) 15 V

(d) 20 V.

**62. Two bulbs of (40 W, 200 V), and (100 W, 200 V). Then correct relation for their resistances (2000)
**

**63. The potentiometer is best for measuring voltage, as (2000)**

(a) it has a sensitive galvanometer and gives null deflection

(b) it has wire of high resistance

(c) it measures p.d. in closed circuit

(d) it measures p.d in open circuit.

**64. The current in the given circuit is (1999)**

(a) 4.9 A

(b) 6.8 A

(c) 8.3 A

(d) 2.0 A

**65. The internal resistance of a cell of e.m.f. 2 V is 0.1 Ω. It is connected to a resistance of 3.9 Ω. The voltage across the cell will be (1999)**

(a) 1.95 V

(b) 1.9 V

(c) 0.5 V

(d) 2 V

**66. In a meter bridge, the balancing length from the left end (standard resistance of one ohm is in the right gap-) is found to be 20 cm. The value of the unknown resistance is (1999)**

(a) 0.8 Ω

(b) 0.5 Ω

(c) 0.4 Ω

(d) 0.25 Ω

**67. A potentiometer consists of a wire of length 4 m and resistance 10 Ω. It is connected to a cell of e.m.f. 2 V. The potential difference per unit length of the wire will be (1999)**

(a) 5 V/m

(b) 2V/m

(c) 0.5 V/m

(d) 10 V/m

**68. The resistance of a discharge tube is (1999)**

(a) non-ohmic

(b) ohmic

(c) zero

(d) both (b) and (c)

**69. Three equal resistors connected in series across a source of e.m.f. together dissipate 10 watt of power. What will be the power dissipated in watt if the same resistors are connected in parallel across the same source of e.m.f.? (1998)**

(a) 30

(b) 10/3

(c) 10

(d) 90

**70. A 5°C rise in temperature is observed in a conductor by passing a current. When the current is doubled the rise in temperature will be approximately (1998)**

(a) 20°C

(b) 16°C

(c) 10°C

(d) 12°C

**71. Three copper wires of lengths and cross¬sectional areas are (l, A), (2l, A/2) and (l/2, 2A). Resistance is minimum in (1997)**

(a) wire of cross-sectional area 2A

(b) wire of cross-sectional area A/2

(c) wire of cross-sectional area A

(d) same in all three cases.

**72. The current in the following circuit is (1997)
**

(a) 2/3 A

(b) 1A

(c) 1/8 A

(d) 2/9 A.

**73. KirchhofFs first law, i.e. Σ i = 0 at a junction, deals with the conservation of (1997, 92)**

(a) momentum

(b) angular momentum

(c) charge

(d) energy.

**74. From the graph between current (I) and voltage (V) is shown below. Identify the portion corresponding to negative resistance (1997) (1997)
**

(a) CD

(b) DE

(c) AB

(d) BC.

**75. A (100 W, 200 V) bulb is connected to a 160 volts supply. The power consumption would be (1997)**

(a) 100 W

(b) 125 W

(c) 64 W

(d) 80 W.

**76. One kilowatt hour is equal to (1997)**

(a) 36 × 10^{-5 }J

(b) 36 × 10^{-4 }J

(c) 36 × 10^{5} J

(d) 36 × 10^{3} J.

**77. If two bulbs, whose resistances are in the ratio of 1 : 2 are connected in series, the power dissipated in them has the ratio of (1997)**

(a) 2 : 1

(b) 1 : 4

(c) 1:1

(d) 1 : 2.

**78. What will be the equivalent resistance between the two points A and D (1996)
**

**79. In the network shown in the figure, each of the resistance is equal to 2 n. The resistance between the points A and B is (1995)
**

**80. Two wires of the same metal have same length, but their cross-sections are in the ratio 3:1. They are joined in series. The resistance of thicker wire is 10 fi. The total resistance of the combination will be (1995)**

(a) 40 Ω

(b) 100 Ω

(c) (5/2) Ω

(d) (40/3) Ω

**81. In good conductors of electricity, the type of bonding that exists is (1995)**

(a) metallic

(b) vander Waals

(c) ionic

(d) covalent.

**82. A heating coil is labelled 100 W, 220 V. The coil is cut in half and the two pieces are joined in parallel to the same source. The energy now liberated per second is (1995)**

(a) 200 W

(b) 400 W

(c) 25 W

(d) 50 W

**83. A 4 µF capacitor is charged to 400 V. If its plates are joined through a resistance of 2 k Ω then heat produced in the resistance is **

(a) 0.64 J

(b) 1.28 J

(c) 0.16 J

(d) 0.32 J.

**84. A wire 50 cm long and l mm ^{2} in cross-section carries a current of 4 A when connected to a 2 V battery. The resistivity of the wire is (1994)**

(a) 4 × 10

^{-6 }Ω m

(b) l × 10

^{-6 }Ω m

(c) 2 × 10

^{-7}Ω m

(d) 5 × 10

^{-7}Ω m

**85. Six resistors of 3 Ω each are connected along the sides of a hexagon and three resistors of 6 Ω each are connected along AC, AD and AE as shown in the figure. The equivalent resistance between A and B is equal to (1994)
**

**86. A flow of 107 electrons per second in a conducting wire constitutes a current of (1994)**

(a) 1.6 × 10^{-12 }A

(b) 1.6 × 10^{26} A

(c) 1.6 × 10^{-26} A

(d) 1.6 × 10^{12} A.

**87. Identify the set in which all the three materials are good conductors of electricity (1994)**

(a) Cu, Hg and NaCl

(b) Cu, Ge and Hg

(c) Cu, Ag and Au

(d) Cu, Si and diamond.

**88. An electric bulb is rated 60 W, 220 V. The resistance of its filament is (1994)**

(a) 870 Ω

(b) 780 Ω

(c) 708 Ω

(d) 807 Ω.

**89. Three resistances each of 4 Ω are connected to form a triangle. The resistance between any two terminals is (1993)**

(a) 12 Ω

(b) 2 Ω

(c) 6 Ω

(d) 8/3 Ω

**90. Current through 3 Ω resistor is 0.8 ampere, then potential drop through 4 Ω resistor is (1993)
**

(a) 9.6 V

(b) 26 V

(c) 4.8 V

(d) 1.2 V

**91. A battery of e.m.f 10 V and internal resistance 0.5 £2 is connected across a variable resistance R. The value of R for which the power delivered in it is maximum is given by (1992)**

(a) 0.5 Ω

(b) 1.0 Ω

(c) 2.0 Ω

(d) 0.25 Ω

**92. The velocity of charge carriers of current (about 1 ampere) in a metal under normal conditions is of the order of (1991)**

(a) a fraction of mm/sec

(b) velocity of light

(c) several thousand metres/second

(d) a few hundred metres per second

**93. In the network shown in figure each resistance is 1 £2. The effective resistance between A and B is (1990)
**

**94. Two identical batteries each of e.m.f 2 V and internal resistance 1 £2 are available to produce heat in an external resitance by passing a current through it. The maximum power that can be developed across R using these batteries is (1990)**

(a) 3.2 W

(b) 2.0 W

(c) 1.28 W

(d)8/9

**95. You are given several identical resistances each of value R = 10 Ω and each capable of carrying a maximum current of one ampere. It is required to make a suitable combination of these resistances of 5 Ω which can carry a current of 4 ampere. The minimum number’of resistances of the type R that will be required for this job is (1990)
**(a) 4

(b) 10

(c) 8

(d) 20

**96. A current of 2 A, passing through a conductor produces 80 J of heat in 10 seconds. The resistance of the conductor in ohm is**

(a) 0.5

(b) 2

(c) 4

(d) 20

**97. 40 electric bulbs are connected in series across a 220 V supply. After one bulb is fused the remaining 39 are connected again in series across the same supply. The illumination will be (1989)**

(a) more with 40 bulbs than with 39

(b) more with 39 bulbs than with 40

(c) equal in both the cases

(d) in the ratio 402 : 392

**98. n equal resistors are first connected in series and then connected in parallel. What is the ratio of the maximum to the minimum resistance ? (1989)**

(a) n

(b) 1/ n^{2}

(c) n^{2}

(d) 1/n

**99. Two batteries of emf 4 V and 8 V with internal resistance 1 Ω and 2 Ω are connected in a circuit with resistance of 9 Ω as shown in figure. The current and potential difference between the points P and Q are (1988)
**

**100. The masses of the wires of copper is in the ratio of 1 : 3 : 5 and their lengths are in the ratio of 5 : 3 : 1. The ratio of their electrical resistance is (1988) **

(a) 1 : 3 : 5

(b) 5 : 3 : 1

(c) 1 : 25 : 125

(d) 125 : 15 : 1σ

### EXPLANATIONS

**1. (c)**

As both metal wires are of identical ! dimensions, so their, length and area of cross- ! section will be same. Let them be / and A \ respectively. Then The resistance of the first wire is

**2. (c)**

The circuit is shown in the figure.

As ammeter is in series with 40.8 Ω

∴Total resistance of the circuit is

R = 40.8 Ω + R_{a} = 40.8 Ω+ 19.2 Ω = 60 Ω

By Ohm’s law,

Current in the circuit is

**3. (d)
**

**4.(e)**

The current flowing in the different branches of circuit is indicated in the figure.

**5. (d)
**The area of cross section of conductor is non uniform so current density will be different but the flow of electrons will be uniform so current will be constant.

**6. (c)
** Required potential gradient = 1 mV cm

^{-1}

V m

^{-1}

Length of potentiometer wire, l = 4 m

^{}

**7.(b)**

Here, Distance between two cities =150 km

Resistance of the wire, R = (0.5 Ω km^{-1} )(150 km)

= 75 Ω

Voltage drop across the wire,

V= (8 V km^{-1}) (150 km) = 1200 V

Power loss in the wire is

**8. (b)**

In the first case

**9. (c)
**The internal resistance of the cell is

**10. (d)**

The situation is as shown in the figure.

**11. (d)
**

**25. (d)**

KirchhofFs junction law or KirchhofFs first law is based on the conservation of charge. KirchhofFs loop law or KirchhofFs second law is based on the conservation of energy.

Hence both statements (A) and (B) are correct.

**56.(a)**

Resistance of a conductor is given by

R = p 1/a , where p is the specific resistance, l is the length and A is the cross-sectional area of the conductor.

Now, when l = 1 and A = 1, R = p.

So specific resistance or resistivity of a material may be defined as the resistance of a specimen

of the material having unit length and unit cross¬section.

Hence, specific resistance is a property of a material and it will increase with the increase of temperature, but will not vary with the dimensions (length, cross¬section) of the conductor.

**57. (a)**

For metals specific resistance decrease with decrease in temperature whereas for semiconductors specific resistance increases with decrease in temperature.

**63. (a)**

**68. (a)**

**73. (c)**

**81. (a)**

**87. (c)**

**92. (a)**