Current Electricity Questions and Answers

In the potentiometer arrangement shown the driving cell D has emf and internal resistance r The cell C whose emf is to be measured has emf E 2 resistance 2r The potentiometer wire is 100 cm long If balanced is obtained the length AJ l a l 50 cm l 50 cm c d and internal A balance will be obtained only if resistance of AB is r s r balance cannot be obtained D r DIH dh E 2r J

0 If the galvanometer current is 10 mA resistance of the galvanometer is 40 92 and shunt of 2 92 is connected to the galvanometer the maximum current which can be measured by this ammeter is a 0 21 A b 2 1 A c 210 A d 21 A

1 A galvanometer of resistance 40 2 gives a deflection of 5 divisions per mA There are 50 divisions on the scale The maximum current that can pass through it when a shunt resistance of 2 2 is connected is

In Maxwell s bridge for calculating unknown inductance the various values at balance are R1 1500 Q2 R2 300 Q2 R3 700 02 C1 0 8 F Calculate R4 L4 Given that in bridge network arm 1 consists of R1 C1 arm 2 and arm 3 consist of R2 and R3 respectively arm 4 unknown arm consists of R4 and L4 5 marks

In the meter bridge circuit shown the null point is obtained at C AC x on the wire AB If the diameter of the wire AB is doubled the position of the new null point C will correspond to A AC x 2 C AC 4x B AC x 4 D AC x A X C www

Q 29 Calculate the current in the 5k ohm resistance Use Thevenin s theorem only 12 kn 48 V 4 k 0 75 mA 0 75 A 0 75 A 0 75 MA 1 75 A www 8kQ 5 kM Load Resistance Sa

In the given circuit two cells of different internal resistance 62 and 22 but same emf are connected in series with external resistance R If potential difference across cell of internal resistance 62 is zero then R is E E 6Q HHWW 1 20 92 3 2 30 R www 22 ww 2 89 4 4 Q

A large network is made of regular hexagonal Units as shown in figure If resistance of each straigh section is r then equivalent resistance of network between the points A and B is 1 A B 2 14 2r 3 3r

Consider the electrical circuit shown in steady state Electrostatic potential energy stored by the capacitor C is how many times the electrical energy stored by capacitor C PH TA UND TEAV VER ALY do ilap R R R C C HH tral OR R www JL RC C C Clarit R t

An ammeter A of finite resistance and a resistor R are joined in series to an ideal cell C A potentiometer P is joined in parallel to R The ammeter reading is lo and the potentiometer reading is Vo P is now replaced by a voltmeter of finite resistance The ammeter reading now is I and the voltmeter reading is V B A www I lo V Vo 1 10 V Vo C1 10 V Vo Correct MY PERF SCO 4 C cut of

To get maximum current through a resistance of 2 22 one can use m rows of cells each row having cells The internal resistance of each cell is 0 5 What are the values of n m if the total number cells is 45 1 3 15 3 9 5 2 5 9 4 15 3

Example 9 In the circuit shown in figure switch S is closed at time t 0 Find a Initial current at t 0 and final current at t in the loop 6 Total charge q flown from the switch c Final charges t 0 d Loss of energy during redistribution of charges e Individual loss across 12 and 22 resistance on capacitors in steady state at time 4F Three capacitors may be assumed liko 1F 40V 10V 222 wwwww 20V 2F 20V 12

tiple Consider the circuit shown below Is is constant current source meaning that no matter what device is connected between points A and B the current provided by the constant current source is always Is the same type questio Is 4R 2R www www 4R ww A B 2R www D If an ideal ammeter is connected between A and B the reading of ammeter is www www A If an ideal voltmeter is connected between A and B the reading of voltmeter is ISR B If an ideal voltmeter is connected between A and B the reading of voltmeter is 21sR C If an ideal ammeter is connected between A and B the reading of ammeter is 9 2F 4R

Under steady state condition 10 Q ww 8 V ALA 0 1 F A 2052 192 B 102 ww 20 Q ww 1024 1 Charge on capacitor is 0 4 C CH 2 Charge on capacitor is 0 2 C D ww C M 10 Q 3 Current in the resistor between point A and B is 0 3 A 4 Current in the resistor between point A and B is 01 A

Calculate the current drawn from the battery in the given network R 12 www R R 5 25 wwww R 55 www E 4V www OR Two metallic wires of the same material have the same length but cross sectional area is in the ratio 1 2 They are connected i In series and ii parallel Compare the drift velocities of

In the circuit shown below a voltmeter of resistance 6 kQ is used to measure the voltage drop across 3 kQ resistance then the reading of the voltmeter is 3 ko ufat fartuchych tech th fahul c Jildl 7d alcHlCk Giulolich 4 KQ www 20 V 60 V 0 20V B 3 10 V C10 3 kQ V

Three identical bulbs A B and C are connected with the voltage supply as shown below When the switch S is closed G increase S Brightness of B and C will increase Baca do A Bar A B Brightness of A B and C will B alocal Sant and chal B Brightness of B and C will decrease Brightness of Band C will remain

A 4 5 m length of copper wire at 20 C has a 3 m long section with diameter 2 2 mm and a 1 5 m long section with diameter 0 8 mm There is a current of 2 3 mA in the 2 2 mm diameter section Resistivity of copper at 20 C is given to be p 1 72x 10 70m a What is the current in mA in the 0 8 mm diameter section b What is the magnitude of the electric field E in V m in the 2 2 mm diameter section c What is the potential difference in V between the ends of the 4 5 m length of wire

a 50 watt 100 watt c 200 watt 150 watt b 100 watt 50 watt d 50 watt 200 watt 1 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 min b 4 min ST IRITSIN 17 c 25 min d 15 min 1ms To 158 In a Wheatstone s bridge all the four arms have equal otor I C

The switch SW shown in the circuit is kept at position 1 for a long duration At t 0 the switch is moved to position 2 Assuming IV021 IV01l the voltage Vc t across capacitor is R Voz 2 SW 1 TVOT STO c R V

Example 3 38 In the circuit shown in figure E 10V E 4V 102 and R 20 Find the potential difference across battery 1 and battery 2 E r1 E2 F T2

pass in cascade as shown in figure A voltage source is connected at port 1 Two port network 1 V Port 2 Two port network 2 13 V3 Port 3 Port 1 Given V A V2 B l2 1 C V2 D112 V2 A2V3 B2l3 12 C2V3 D213 A1 B C D1 A2 B2 C2 and D2 are the generalized circuit constants If the Thevenin equivalent circuit at port 3 consists of a voltage source V and an impedance ZT

To identical conducting spheres carrying dill Charges attract each other with a force F when placed in air medium at a distance d apart The spheres are brought into contact and then taken to their original positions Now the two spheres repel each other with a force whole magnitude is equal to that of the initial attractive force The ratio between initial charges on the spheres is a 3 8 only b 3 8 only k 3 8 or 3 8

se in ce 99 A potentiometer wire of length 200 cm has a resistance of 20 2 It is connected in series with a resistance of 10 92 and an accumulator of emf 6 35 d 2 08 Q 1022 6V 24V G 6 V having negligible internal resistance A source of 2 4 V is balanced against a length L of the potentiometer wire The value of Lis a 100 cm b 120 cm c 110 cm d 140 cm 100 A potentiometer wire of length 100 cm 3

b 2 05 V d 6 05 V c 4 05 V 97 3 V potentiometer used for the determination of internal resistance of a 2 4 V cell The balance point of the cell in open circuit is 75 8 cm When a resistor of 10 2 2 is used in the extern circuit of the cell the balance point shifts to 683 length of the potentiometer wire The inter resistance of the cell is a 2 59 c 1 12 92 16V 1020 b 2 259 d 3 222 F 1 In E E C

Given circuit represents an ammeter Resistance of each Galvanometer coil is 1000 and shows maximum deflection at 10mA current Range of ammeter is A 22 mA C 28 mA 100002 G G ww 5002 B 26 mA D 24 mA

96 In a potentiometer a cell of emf 1 5 V gives a balanced point at 32 cm length of the wire If the cell is replaced by another cell then the balance point shifts to 65 0 cm then the emf of second cell is

95 AB is a wire of potentiometer with the increase in the value of resistance R the shift in the balance point will be a towards B b towards A c remains constant d first towards B then back towards A 96 In a potentiometer a cell of emf 15 Y gia

c 40 cm d 20 cm 2 A wire connected in the left gap of a meter bridge balance a 10 2 resistance in the right gap to a point which divides the bridge wire in the ratio 3 2 If the length of the wire is Im The length of one ohm wire is b 0 067 m a 0 057 m d 0 134 m c 0 37 m

In a common emitter transistor amplifier using output resistance of 5000 2 and input resistance of 2000 2 if the peak value of input signal voltage is 10 mV and 50 then the peak value o output voltage is 1 5 x 10 6 V 3 125 V 2 12 5 x 10 4 V 4 1 25 V

A battery of emf E is connected across a conductor as shown as one observe from A to B then B MEDA A B C Current remains same Drift velocity of electron decreases Electric field decreases

a very long time All circuit elements are considered to be ideal Which one of the following statements best describes the behavior of the current through the switch S once it is closed 9 V 3 KQ www S 1 KQ www C The current initially is 12 mA and decreases to a steady 3 mA The current initially is 3 mA and increases to a steady 12 mA The current initially is 9 mA and decreases to a

Calculate the current in a wire if 700 C of charge passes through it in 15 minutes Electric potential at a point in an electric field is 0 5 V when charge of 3 C was broug from infinity to that point Calculate the work done Ans 1 5

c 1 3 A d I A 5 A circuit has a section ABC as shown in figure If the potentials at points A B and C are V V and V respectively The potential at point O is a V V V b R R R R c Zero d R R R 1 R R R R

86 Four resistances of 352 352 352 and 4 52 respectively are used to form a Wheatstone bridge The 42 resistance is short circuited with a resistance R in order to get bridge balanced The value of R will be a 102 b 112 c 122 d 132

Consider the circuit shown below Is is a constant current source meaning that no matter what device is connected between points A and B the current provided by the constant current source is the same Connect an ideal voltmeter between A and B Determine the voltage reading in terms of any or all of R and Is 4R 2R 4R www A B 2R www W 2R 4R

d 7 A IN In the circuit shown current flowing through 25 V cell is a 7 2 A b 10 A c 12 A d 14 2 A 10 V SV 20 V 30 V 25 V T 50 100 50119 onen switch and a P

Cument Electricity 79A7V battery with internal resistance and a 3 V battery with internal resistance 192 are connected to a 10 2 resistor as shown in figure the current in 10 Q resistor is a 0 27 A 0 031 A 7V 20 301 3 V 19 b 0 31 A d 0 53 A alue of currents fu hand 85 In an she a 86 For are res ore a

c 0 031 A In the circuit shown the value of currents I I and l are 2A2A a 3 A A b A 3 A A c 5 A 4A 3 A d 7 A A A liv 24 V 40 www 27 V 202 ww 692 www incit shown current flowing through 25 V 8 8

69 In a circuit a cell with internal resistance r is connected to an external resistance R The condition for the maximum current that drawn from the cell is a R r c R r b R r d R 0

5 Two cells and E connected in opposition to each other as shown in figure The cell is of emf 9 V and internal resistance 3 2 the cell e in of emf 7 V and internal resistance 752 The potentia difference between the points A and B is c 7 8 V a 8 4V b 5 6V d 6 6 V

58 Three resistors 2 52 42 and 5 2 are combined in parallel This combination is connected to a battery of emf 20 V and negligible internal resistance The total current drawn from the battery is a 10A b 15 A c 19 A d 23 A

c V d R 65 A battery of emf 15 V and internal resistance of 42 is connected to a resistor If the current in the circuit is 2 A and the circuit is closed Resistance of the resistor and terminal voltage of the battery will be a 2 552 6 V b 3 5 2 6 V d 3 592 7 V c 2 592 7 V 66 The battery of a trunk has an emf of 24 V If the

55 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 a 352 c 622 b 6 Q d 0 6m 2 56 A and B are two points on a uniform ring of resistance 15 2 The a c 63 An 14 con

c 2 5 52 66 The battery of a trunk has an emf of 24 V If the internal resistance of the battery is 0 8 2 What is the maximum current that can be drawn from the battery a 30A b 32A c 33 A d 34 A

62 In the circuit shown in the given figure the resistances R and R are respectively R 0 5 A 69 V a 142 and 40 92 c 40 92 and 30 52 20 2 b 40 2 and 1492 d 14 22 and 30 92

Cument Electricity 52 resistors each of resistance R first combine to give maximum effective resistance and then combine to give minimum effective resistance The ratio of the maximum to minimum resistance is a n b n c n 1 d n

c 652 56 A and B are two points on a uniform ring of resistance 15 2 The ZAOB 45 The equivalent resistance between A and B is a 1 64 92 b 2 84 92 c 4 57 92 d 2 64 2 G 63 VI

53 The equivalent resistance between A and B for the circult shown in figure is a 13 12 b 15 12 c 17 12 d 19 12 492 502 D 652 802 E 502 ulindrical tube has inner radius a and c 2 60 The rea a 6 5 b 3 2 c 2 5 d 1 4 61 Three

9 Five equal resistances of 10 22 are connected between A and B as shown in figure The resultant resistance is A 102 www 10 52 ww a 102 b 52 102 www 1092 c 152 ww 1002 d 692