Current Electricity Questions and Answers

The figure shows three circuits with identical batteries inductors and resistors Rank the circuits in the decreasing order according to the current through the battery i just after the switch is closed and ii a long time later 1 reeeeeee 2 Question Type Single Correct Type 1 1 i 12 13 11 1 0 ii 2 3 1 0000000 ol www 3

Two cells of emf 2V and 3V and internal res istances 1ohm and 2ohm respectively are C onnected in parallel across a 10ohm resisto r Calculate the current in each cell and the c urrent through the 10ohm resistor

Q 20 A uniform conducting wire is used to make a ring and its two diameters AB and CD The ring is placed in a uniform magnetic field B perpendicular to its plane The resistance of the wire per unit length is 2 m pe X C X B O A X X D x X X B QvB Tra

Choose the correct statement a A capacitor can conduct a de circuit but not an inductor b In a de circuit the inductor can conduct but not a capacitor c In de circuit both the inductor and capacitor cannot conduct d The inductor has infinite resistance in a de circuit

21 Potentiometer is an apparatus used for measuring the emf of a cell or potential difference between two points in an electrical circuit accurately It is also used to determine the internal resistance of a primary cell The potentiometer is based on the principle that if V is the potential difference across any portion of the wire of length 1 and resistance R then V x 1 or V kl where k is the potential gradient Thus potential difference across any portion of the wire of length is directly proportional to length of the wire of that portion The potentiometer wire must be uniform The resistance of potentiometer wire should be high Primary circuit Secondary circuit A i Which one of the following is true about potentiometer a Its sensitivity is low b It measures the emf of the cell very accurately

The length of potentiometer wire is 1 m and its resistance is 40 A current of 5 mA is flowing in it An unknown source of emf is balanced on 40 cm length of this wire The emf of the source is 05mV 06 mV O 12 mV 08 mV

ii Sensitivity of a potentiometer can be increased by a Decreasing potential gradient along the wire b Increasing potential gradient along the wire c Decreasing current through the wire d Increasing current through the wire

A current of 1 mA is flowing through a potentiometer wire of length 4cm and of resistance 49 The potential gradient of the potentiometer wire is a 10 V m b 10 5 V m c 2x10 V m d 4 10 V m

A meter bridge is set up as shown to determine an unknown resistance X using a standard 10 ohm resistor The galvanometer shows null point when tapping key is at 52 cm mark The end corrections are 1 cm and 2 cm respectively for the ends A and B The determined value of X is O X 1002

16 A freighter is 240 km due cast of a harbour A current is flowing due south and the freighter captain wishes to set a course so that he can reach the harbour directly He sets the course at 22 6 north of west and sets a speed through the water of 13 kmh and the freighter eventually reaches the harbour in 20 hours A Define the RESULTANT of two vectors B Calculate the resultant velocity of the freighter C Draw a velocity vector diagram indicating the velocity of the current v the velocity of the freighter through the water ve and the resultant velocity of the freighter v showing how they are related D Datering the valocity mant

Heat generated in a circuit is given by Q i2Rt where i is the current R is resistance and tis time If the percentage errors in measuring i R and t are 3 1 and 2 respectively then the maximum percentage error in measuring heat generated in the circuit is

Q 8 www ww 4 Effective resistance between point A and B for following network is each branch of resistance is R R 1 07 12

Figure shows an electric circuit contain four resistors of equal resistances 4 2 Cells E E2 E3 are ideal of unknown EMF whereas cell E4 has some unknown internal resistance and EMF 4V It is found that current through EA DH FB and HE are 7A 6A 2A and 5A respectively as shown in figure A Internal resistance of E4 is 192 B Current through DC is 0 5 A C Current through AD is 5 5 A D E2 6V E 5A E 7A A R B E R R 6A D H E

14 In the given electrical networks shown in Figs 3 185 a and b identical cells each of emf E are giving same current I Find the values of the resistors R and R in the network b Ans 9 90 1192 R R b 1 10 3 114

Q of an emf lower than Q 18 Twelve wires each having resistance of 32 are connected to form a cubical network A battery of 10V and negligible internal resistance is connected across the diagonal opposite corners of this network Determine its equivalent resistance and the current along each edge of the cube

9 Using Kirchhoff s rules determine the value of unknown resistance R in the circuit shown in Fig 3 180 so that no current flows through 402 resistance Also find the potential difference between A and D CBSE D 12 Ans 3 V F 10 www A 192 9 V E B 402 6V H 3 V D C R

A wire is carrying 2 A current from left to right Drift speed of electron in conductor is 1 mm s A person is moving towards right with 1 mm s velocity parallel to conductor Average velocity of electron with respect to this person 1 1 mm s 2 Zero 3 2 mm s 4 Can t be said

In steady state current flow through resistance R in given figure R wwww E E 2R E 3R EIR 2R wwww 0000 L

A voltmeter reads 3 V at full scale deflection and is graded as 6000 2 V What resistance should be connected in series with it so that it reads 12 V at full scale deflection A 1 8 104 S C 5 4 10 2 B D 3 6 104 7 2 x 10

0 Three resistons are connected as sheron through the resistor 5 2 a current of 1A is flowing A 1 what is the current the through other two resistiers 0 64 0 447 11 what is p d across AB and AC 5V 11V A 51 8 10 1 Tumour 15 1

Three identical resistors R R and R3 are connected as shown in figure When the switch S is closed A Select answers B C www R D www R www R power dissipated in R increases power dissipated in R increases total power delivered by the cell increases power dissipated in R is less than that in R

Three identical bulbs B B2 and B3 are connected in the arrangement as shown in the figure Choose the INCORRECT statement Select an answer A B B C P P2 P3 R R R3 V V V3 D 13 11 12

7 AB is a wire of potentiometer with the increase in the value of resistance R the shift in the balance point J will be R A B a towards B b towards A c remains constant d first towards B then back towards A

A cylindrical conductor has length inner radius a and outer radius 2a The resistivity p varies with radial distance Por r from the axis as p a conductor for radial flow of current will be Po 2 l a r 2a The resistance of the 7 O Poln2 2 l

When two known resistances R and S are con nected in the left and right gaps of a metre bridge the balance point is found at a distance from the zero end of the metre bridge wire An unknown resistance X is now connected in parallel to the resistance S and the balance point is now found at a distance 1 from the zero end of the metre bridge wire Obtain a formula for X in terms of 7 12 and S C 1 100 1 20 m R 100 12 A X ww S B

The equivalent resistance of the network shown in the figure between points P and Q is 10 N W C 2 3 C 3 C 12 12 12 12 1222 12

Column 1 gives the circuit condition and Column 1 gives the value of R for maximum power consumption across R and value of maximum power Po dissipated across R corresponding to the value of R Column l Q1 Q2 Q3 Q4 4 V 6 V 3 V 12 V 4 V R 10 V R R R 292 ww 692 3Q wwww 1292 492 492 402 www www 392 Column II A1 Po 3 W A2 R 20 A3 Po 2 W A4 R 3 Q A5 R 50

Two light bulbs shown in the circuit have ratings A 24 V 48 W and B 24 V and 36 W as shown Wi the switch is closed 12 V 12 V BO OPTIONS MARK FOR REVIEW CLEAR SELECTION D A de R A 24 V 48 W 824 V 36 fear a The intensity of light bulb A decreases and of Bincreases JAPA BROLIS The intensity of light bulb A as well as Bincreases

b i 1 1200 m r 0 6 cm Figure Q1 b i r 0 6 cm X Conductor plates d 2 mm Figure Q1 b ii A solid cylindrical copper conductor has dimension such as represented in Figure Q1 b i It carries a total current of 50 ampere in the y direction Derive and solve the mathematical expression of resistance for the conductor structure and then calculate the power dissipated within it using the Joule s law Conductivity o of copper is 5 8 107 5 marks

19 Current sensitivity of a moving coil galvanometer increased by 20 when its resistance is increased by a factor 2 twice The change in voltage sensitivity is a 25 increase b 25 decrease c 40 increase d 40 decreases

along edge 19 You are required to select a carbon resistor of resistance of 36 x 10 5 fr shop keeper What would be the sequence of colour bands to code the desired resistor Why do carbon resistors find extensive use in electronic circuits in the f

SolveLancer Test By changing the magnetic flux through a coil of resistance 500 a current is induced in the coil as shown in the graph below The magnitude of change in flux through the coil is 30 a b c d Current A SolveLancer Test Time s 1 125 x 102 Wb 4 5 x 10 Wb 2 25 x 104 Wb 1 125 x 104 Wb 1 5

The drift speed of free electrons in a conductor is 0 1 m s and the electric field in the conductor is 5 x 10 2 V m The mobility of the free electrons is O 1 0 x 10 3 m V 1 s 1 O 1 5 x 10 3 m V 1 s 1 O2 0 x 10 3 m V 1 s 1 O 2 5 x 10 3 m V 1 s 1

15 Dust Cloud Ignition Caused due to Static Electricity A case study investigates the reasons behind the ignition of dust cloud during a manual powder processing About 18 kg of combustible powder was tipped from a plastic drum into a metal vessel The powder had minimum ignition energy of 12 m It was noticed that there was an ignition of dust cloud formed at the top of vessel due to pouring of powder To verify the theory of this ignition 18 kg of same powder was tipped from a similar drum into Faraday Cage Surface area of the chime was about 0 0641 m Total charge created by the movement of powder was 3 6 C The maximum charge density of surface in air is equivalent to 27 C per square metre The capacitance of chime was estimated to be 71 pf Using the above information and understanding of basic concepts of electrostatics answer the following 1 The cause of ignition is are a charging of powder due to friction c developed potential difference 2 The total charge density of the chime is a 27 C m c 72 C m 3 The maximum charge on the chime is a 1 7 x 10 C c 3 6 C 4 Voltage of the chime is a 2400 V c 24 KV 5 S I unit of charge density is a cm3 c Cm b 56 x 106C m d 65 x 10 C m b 7 1 x 10 C d 6 3 C Plastic drum with metal Chime Ring b 4200 V d 42 KV b C cm 2 d cm b induced charge on the metal drum d all of these

If H and H are amounts of total heat generated in a resistance R due to charge Q passing through it when current i through it changes in following ways a Decreases down to zero uniformly during a time interval T b Decreases down to zero becoming times of its value after every time T H Find H e

A cylindrical conductor of length L and radius R is connected between two plates which are maintained at a constant potential difference V see figure The conductivity of the cylindrical conductor varies across its cross section as where r is the radial distance from the J 00 r R centre axis of the conductor and oo is a constant The current through the conductor is R L

A microammeter has a resistance of 10002 and full scale range of 50 A It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it Pick the correct range and resistance combination 1 50 V range with 10k resistance in series 925 10 V range with 200k 3 10 mA range with 1 9 4 10 mA range with 0 1 resistance in series resistance in parallel resistance in parallel

he switch S is closed at t 0 as shown in the figure R 302 www www R 60 36 V 1H D R 602 R 302 The current as function of time in the inductor is 3 1 e A The current through R just after closing of switch is 8A The power supply by the battery as function of time is 108 1 e W The current through R after a long time closing of switch is 3A

P www In the given figure a circuit is shown In this figure galvanometer G will have zero deflection only when O PQ RS PR QS OPS QR Q R S www G O For any relation between resistance III

9 6 when current passes through it if average The resistance of nichrome becomes 85 8 Nichrome has resistance of 75 3 2 at 30 C of nichrome now is 1 700 C 2 750 C 3 850 C 4 900 C 10 The incorrect statement among the following statements is NCERT Pg 111 1 Emf of a cell is the potential difference between its positive and negative electrodes in an open circuit 2 Internal resistance of dry cells is much higher than common electrolyte cells 3 The terminal potential difference of can be zero 4 When current passes from 11 When a current of its negative to pr difference ar A is flowir a poter batt NCERT Pg 105 negative terminal of a terminal potential its emf ference free 7 diffe validity of Kirchhoff s or reorienting the wire does not Energy law Junction rule is based on conservation total potential change must be zero point if we come back to same point

Two resistors of resistances 200k2 and 1M22 respectively form a potential divider with outer junctions maintained at potentials of 3V and 15V Then the potential at the junction between the resistors is O 1 V O 0 6 V O 0 O 12 V O 12 V Mark for review later

Two cells of equal e m f and of internal 3 resistances r and r r r are connected in series Now they are connected to an external resistance R it is observed that the potential difference across the first cell becomes zero The value of R will be 1 r 1 1 12 3 4 r f 2 11 12

8 V 6 V 202 ww 20 www R ww 1 7 A 2 10 A 3 2 A 4 8 A 13 When a metal conductor connected to right gap of meter bridge is heated the balancing point from left end NCERT Pg 120 1 Shifts towards left 2 Shifts towards right 3 Remains unchanged 4 Shift to zero position 14 Resistance P Q S and R are arranged in clockwise cyclic order to form a balanced wheatstone bridge The ratio of electric power consumed in the branches P Q and R S is NCERT Pg 109 1 1 1 2 R P 3 R P 4 Q S 15 A battery of e m f 5 V and negligible internal resistance is connected across the diagonally opposite corners of a cubical network consisting of 12 resistors of network each of resistance 1 2 The current along one edge of the cube is NCERT Pg 116 1 1 A 2 2 A 3 3 A 4 4 A 16 Four arms of wheat stone bridge have t following resistances AB 600 BC 100 2 CD 60 2 DA 12 Q galvanometer of 15 2 is connected acro BD Calculate the value of addition resistance connected across CD to balan the bridge NCERT Pg 11 A 60 Q 1 12 Q 3 180 2 129 B G 5 V D 100 92 15 02 60 22 2 15 2 C

Two parallel resistance less rails are connected by an inductor of inductance L at one end as shown in the figure A magnetic field B exists in the space which is perpendicular to the plane of the rails Now a conductor of length mass m and neglible resistance is placed transverse on the rails and given an impulse J towards the rightward direction Then choose the correct option s A PART TERR fache facci 21 R Bu ya E elteile 3 J Lm BO A Velocity of the conductor is half of the initial velocity after a displacement of the conductor 3 J L d 4B m B Current flowing through the inductor at the instant when velocity of the conductor is half of the initial velocity is i 3J V4Lm C Velocity of the conductor is half of the initial velocity after a displacement of the conductor 3J L d VB 2m D Current flowing through the inductor at the instant when velocity of the conductor is half of the initial velocity is i

A storage battery of emf 8 0 V and internal 29 resistance 0 50 is being charged by a 120 V dc supply using a series resistor of 15 50 terminal voltage of the battery during charging 1 10 5V 2 9 5V 3 8 5V 4 11 5V

A wire of resistance 120 m is bent to form a complete circle of radius 1 cm The resistance between its two diametrically opposite points A and B as shown in the figure is 2 the value of n is 100 A B

is A resistance of 2 Q2 is connected across one gap of a metre bridge the length of the wire is 100 cm and an unknown resistance greater than 2 connected across the other gap When these resistance are interchanged the balance point shifts by 20 cm Neglecting any corrections the unknown resistance is A 322 0 59 B 42 D 60

59 Consider the circuit shown in the figure In which resistor the amount of power dissipated is the largest 60 A RI B R2 C R3 D R4 A biconvey long with R1 200 R2 50 V1 R3 50 R4 100

A galvanometer has a resistance of 822 It gives a full scale deflection for a current of 10 mA It is to be converted into an ammeter of range 5A The only shunt resistance available is of 0 02 22 which is not suitable for this conversion Find the value of resistance R that must be connected in series with the galvanometer figure to get an a ammeter of the desired range

2221 222 47 7 What is the phase angle between the voltages of the inductor and capacitor in a RLC series circuit A 0 B 45 C 90 D 180 E 270 series circuit contains a 1 0 k f resistor a 5 0 mF capacitor and an ideal 25 V er supply What is the time constant for the circuit A 5 0 s 3 5 0 s 1 6 us