Current Electricity Questions and Answers

A bimetallic strip consists of metais A and B It is mounted rigidly as shown The metal A has higher coefficient of expansion compared to that of metal B When the bimetallic strip is placed in a cold bath it will Neither bend nor shrink Bend towards the left Not bend but shrink Bend towards the right A B

For an ohmic substance the electron drift velocity is proportional to A the cross sectional area of the sample B the length of the sample C the mass of an electron D the electric field in the sample E none of the above

Paragraph for Question Nos 15 to 19 Consider the circuit diagram shown and answer the questions based on it 1 3 1 15 What is the equivalent resistance of the three resistors on the left to the 6 V cell in the above figum 1 10 2 2 92 3 52 4 492 16 What is the current drawn from the cell in the circuit 1 6 A 1 15 1 A 2 3 10 2 www A 20 2 www 10 2 3 4 A 3 17 What is the current through the 20 2 resistor on the left of the 6 V cell in the figure V 6 V 2 2 2012 www 10 2 www 2012 4 2 A 3 4 15 15 18 What is the voltage drop across the three resistors on the left of the 6 V cell in the figure 2 6 V 2 2 A 2 15 4 8 3 4 V 3 19 What is the current through the 10 2 resistor on the right of the 6 V cell in the figure A A 1 A

5 A A mixer is operated with 230V of AC supplied with a power rating of 460W for one minute Fin the current flowing through the mixer and the number of electrons flowing in one minute B Calculate the total resistance of the circuit shown 2 3 4Q www 30 m 20 Rth 20 1Q B 19 C 0 592 D

For the circuit arrangement shown in the figure the circuit is switched on and the variable resistance is adjusted such that the bulb just glows Now if the circuit is switched off www Option A B C D the bulb stops glowing momentarily the bulb becomes dim and then stops glowing momentarily the bulb becomes very bright and then stops glowing the bulb continues to glow for some time and then stops glowing Rate this questi

23 The V graph of a conductor at two different temperatures is shown in figure The ratio of temperature TA and Tis B V 1 tan20 3 sec 0 0 0 T B A 2 cot 0 4 cosec 0 having an internal resistanc

22 The resistances in the two arms of the meter bridge are 5 and R 22 respectively When the resistance R is shunted with an equal resistance the new balance point is at 1 6 1 The resistance R is 2014 TY mort a 10 AL 1 522 b 15 G RQ oftal B 100 1 OURY gniw c 20 Q 8 d 25 Q

The resistance of four arms P Q R and S in a Wheat stone s bridge are 5 10 6 and 120 respectively The emf and internal resistance of the cell are 18V and 9 respectively If the galvanometer resistance 11 is 100 Q then the current drawn from the cell will be A B C D 3A 2A 4A 5A

The mechanical equivalent of heat is 1 cal 4 18 J A heating coil connected to a 120 V source provides 60 000 calories in 10 minutes The current in the coil is A 0 83 A B 2 A C 3 5 A D 20 A E 50 A

When titrating V and using diphenylamine sulfonic acid E 0 85 V fo the color change indicator which of the following one electron reagents oxidized form should be used as the titrant V e E 0 255 V

the figure a long uniform potentiometer wire AB is having a constant potential gradient along its length The null points for the two primary cells of emfs E and E connected in the manner shown are obtained at a distance of 120 cm and 300 cm from the end A A 300 cm 120 cm E E2 THI E E2 Find i E E and ii position of null point for the cell E the B sonsi of

voltage to By increasing the transmission double of its original value the same power can be dispatched keeping the line loss 1 equal to original value 2 3 4 half the original value double the original value one fourth of original value

A 69 0 F capacitor is connected to a generator operating at a low frequency The rms voltage of the generator is 3 80 V and is constant A fuse in series with the capacitor has negligible resistance and will burn out when the rms current reaches 18 0 A As the generator frequency is increased at what frequency will the fuse burn out Number i Units

of identical 2 A number emf E connected cells n each of resistance internal I in series are charged by a DC source of emf E using a resistor R i Draw the circuit arrangement ii Deduce the expressions for a the changing current and b the potential difference across the combination of the cells

Question 4 NO SOLUTION REQUIRED CONSIDERED AS MULTIPLE CHOICE QUESTION A ring shaped conductor a 0 714 m in radius carries a total charge of Q 580 nC uniformly distributed around it As shown in the figure a point charge q 50 0 nC is placed at the point P which is on the axis of the ring and x 0 732 m from its center What is the magnitude of the electrostatic force acting on charge q by the ring Q 10 points a 1 79x10 N b 2 50x10 N c 3 57x10 N d 4 99x10 N e None of the above X

1 Two cells of emf 2E and E with internal resistance r and r respectively are connected in series to an external resistor R see figure The value of R at which the potential difference across the terminals of the first cell becomes zero is 1 1 1 ol 2 vi 2E 2E Official Ans by NTA 2 2E E www R 3E i R 1 1 TPD 2Eir 0 2E ir wwww R 2 3Ex 1 R 1 5 92 12 w www t 1 E 4 1 1

A resistor with resistance 10 MQ is connected in series with capacitor with capacitance 1 0 F and a with emf 12 0 V Before the switch is closed at time t 0 the capacitor is uncharged C E R www R www S S 63 Find the time constant when S is closed and before that the capacitor is charged through S and S is op 1 5 s 2 10 s 4 40 s 3 20 s 54 When S is closed for charging the capacitor the current in the circuit at t 0 S is open 1 1 2 A 2 1 8 A

The circuit given below contains five identical resistors The 45V battery delivers 58W of power to the circuit R ww 45 V wwwwww O 2002 O 250 O 300 R wwww The resistance R of each resistor is R3 RA www R5

44 Find the potential of B point in given circuit 10 V A 1 11 2 F 1 7 5 V 3 5 V 5 VAI B 2 F 2 15 V 4 Zero

59 Figure shows a network of eight resistors numbered 1 to 8 each equal to 202 connected to a 3V battery of negligible internal resistance The current I in the circuit is 3V a 0 25 A to min B min ming 3 b 0 5 A E 8 wwww F c 0 75 A d 1 0 A

In an experiment to measure the internal resistance of a cell by potentiometer it is found that the balance point is at a length of 2m when the cell is shunted by a 42 resistance and at 3m when cell is shunted by a 852 resistance The internal resistance of cell is 3 169 1 120 2 802 4 10 The flux linked with a coil at any instant t is given by 10 50r 250 The induced emf at t 3s

A simple potentiometer circuit is shown in the figure The internal resistance of the 4V battery is negligible AB is a uniform wire of length 100 cm and resistance 202 What would be the length AC for etphysicskota co galvanometer deflection 1 5 V 2 40 ww C kota

The input resistance of a silicon transistor is 100 W Base current is changed by 40 uA which results in a change in collector current by 2 mA This transistor is used as a common emitter amplifier with a load resistance of 4 KQ The voltage gain of the amplifier is 2012M a 2000 c 4000 b 3000 d 1000

12 cells each having the same emf are connected in series and are kept in a closed box Some of the cells are wrongly connected This battery is connected in series with an ammeter and two cells identical with each other and also identical with the previous cells The current is 3 A when the external cells aid this battery and is 2 A when the cells oppose the battery How many cells in the battery are wrongly connected A 1 B 2 C 3 D 4

19 A network of resistances is connected to a 16V battery with internal resistance of 102 as shown in 4102 402 16V HH The equivalent the voltage drops V B AB 192 192 1202 1 7 ohms 4V 2V and 8V 2 2 ohms 4V 2V and 8V 3 7 ohms 2V 4V and 8V 4 6 ohms 4V 2V and 4V 652 resistance of the network and VBC and VCD are I D

Question Fuse Miniature Circuit Breaker MCB and Earthing System are the important protection systems used in House wiring The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as Answer Your Question A domestic wiring B electrical earthing CO industrial wiring D none of the above

3 18 The resistance Re of the coil of a pivoted coil galvanometer is 9 3652 and a current of 0 0224 A causes it to deflected full scale We want to convert this galvanometer to an ammeter reading 20 0 A full scale The only shunt available has a resistance of 0 025002 What resistance R must be connected in series with the coil of galvanometer RG R B

3 2 For the given circuit shown in figure 3 373 in the steady state condition charge on the capacitor is 16 C If the battery is removed and the junctions A and C are shorted Find the time during which charge on the capacitor becomes 4 C and the EMF of battery 1923 A 252 www w 452 D 352 www C 4 F THE E 452 Figure 3 373 352 C

www A B Circular Wire Loop 33 In the circuit drawn above the switch S is initially open and the capacitor C is charged with the polarity indicated The switch is then closed and the capacitor begins discharging through the resistor Which of the following is true of the current that is subsequently induced in the circular wire loop near the long straight wire AB A It is counterclockwise and constant B It is counterclockwise and increases with time C It is counterclockwise and decreases with time D It is clockwise and increases with time E It is clockwise and decreases with time

Page 3 RE BOARD EXAM e 3 i The potential of point Bis a 16 V b 24 V c 32 V d 36 V ii If a galvanometer is connected between Band D the direction of current through galvanometer is a B to D b D to B c depends on resistance of galvanometer d in the beginning from B to D and later on from D to B iii For what additional value of the resistance in arm BC in series parallel would make the bridge balanced a 220 b 20 c 20 Q d 44 Q iv In Wheatstone method the instrument used as null detector is a ammeter b galvanometer c voltmeter these 100 Q d none of

If 2 bulbs rated 2 5 W 110 V and 100 W 110 V are connected in series to a 220 V supply then A 2 5 W bulb will fuse B 100 W bulb will fuse D both will not fuse C both will fuse Five identical resistor each of 12 are initially arranged as shown in the figure by clear lines If two similar resistances are added as shown by the dashed lines then change in resistance in final and initial

A 900pF capacitor is charged by 100V battery The capacitor is disconnected from the battery and connected to another capacitor of 800 pF capacitor What is the electrostatic energy stored by the system

33 In each of the following circuits what is the equivalent resistance between A and B All resistors have same value i e R a A wwwww c A e A wwwwww wwwww www www wwwww B B b A www B d A wwwww B

When a galvanometer is shunted with a 402 resistance the deflection is reduced to one fifth If the galvanometer is further shunted with a 202 wire the further reduction in the deflection will be the main current remains the same A 8 13 of the deflection when shunted with 492 only B 5 13 of the deflection when shunted with 402 only C 3 4 of the deflection when shunted with 402 only D 3 13 of the deflection when shunted with 40 only A resistor of resistance B is connected to a cell of internal resistance 5 Q2 The value of R is varied from

24 When two resistances are connected in parallel then the equivalent resistance is When one of the resistance is removed then the effective resistance is 252 The resistance of the wire removed will be 3 6 1 3 ohm 2 2 ohm 3 ohm 4 ohm

3 A galvanometer of resistance 20 2 gives a full scale deflection when a current of 0 04 A is passed through it It is desired to convert it into an ammeter of full scale reading 20 A The only shunt available is 0 05 92 resistance The resistance that must be connected in series with the coil of the galvanometer is a 4 95 0 b 5 94 9 c 9 45 d 12 62 S

3 17 A moving coil galvanometer of resistance 2002 gives a full scale deflection when a current of 1mA is passed through it It is to be converted into an ammeter reading 20A on full scale But the shunt of 0 00502 only is available What resistance should be connected in series with the galvanometer coil Ans 79 99522

n a circuit containing 16 nodes arranged in circular fashion a node is connected to every other node by a resistor of resistance R Then equivalent resistance between two consecutive nodes is O O 8 R 16 R 4

In the following network the voltage magnitudes at all buses are equal to 1 pu the voltage phase angles are very small and the line resistances are negligible All the line reactances are equal to j10 Bus 1 slack j192 Bus 2 j10 S Bus 3 P 0 2 pu If the base impedance and the line to line base voltage are 100 ohms and 100 kV respectively then the real power in MW delivered by the generator connected at the slack bus is P 0 1 pu j102

In a closed circuit to maintain a steady current an external agency moves electrical charge from 1 Lower to higher potential energy 2 Higher to lower potential energy 3 Lower to higher potential 4 Higher to lower potential

twork of resistance is constructed with R and R as shown in the figure The potential at the point 1 2 N are V V2VN respectively each having a potential k times smaller than previous on R Va m m V R q no 2

In figure circuit section AB absorbs energy at the rate of 5 0W when a current i 1 0 A passes through it in the indicated direction A R 2 02 E B a What is the potential difference between points A and B b Emf device X does not have internal resistance What is its emf c What is its polarity the orientation of its positive and negative terminals

203 The terminals of a 18 V battery with an internal resistance of 24 22 are connected to a circular wire of resistance 24 at two points distant at one quarter of the circumference of a circular wire The current through the bigger arc of the circle will be a 2 25 A b 3 A c 0 75 A d 0 16 A 2 20

Capacitor of given system is C Find the capacitance if dielectric is removed A is the area of plate K dielectric constant A 43 C3 ectric C B C D A 3 K 2 d 1017 itor ic filled with two dielectrics of thickness d and d

287 To the potentiometer wire of length L and 10 resistance a battery of emf 2 5 volts and a resistance R are connected in series If a potential difference of 1 volt is balanced across L 2 length the value of R in 2 will be a 1 c 2 b 1 5 d 2 5 AMU Med

The resistance of a bulb filament is 10002 at a temperature at 100 C If its temperature coefficient of resistance be 0 005 C then its resistance will become 2002 at a temperature of A 300 C B C D 400 C 500 C 200 C

A total resistance of 2 is produced by combining an unknown resistor R with a 3 resist What is the value of R and how it is connected to 32 resistor A 4 S2 parallel C 6 22 parallel Why it is difficult to write on a waxed paper A Due to large friction C Due to low quality of pen B 5 92 parallel D 32 series B Due to very low friction D none of these

Consider the following combination of cells A and B which are 6V Cell A 1 12 V 28 To obtain the current through X the circuit can be consider to be made up of a single cell of 1 Emf 10 V internal resistance 2 9 2 Emf 9 V internal resistance 2 3 Emf 10 V internal resistance 0 5 2 4 Emf 12 V internal resistance 2 2 Www 292 wwww 302 29 The current through X is 1 1 A 3 0 5 A 30 The current supplied by cell A is 1 1 A 3 0 5 A 31 The current supplied by cell B is 1 1 A 2 2 A 3 0 5 A 4 Zero 32 Which two of the four circuits given below are identical with respect to the current through resistor 5V 7V 2 V 1 22 18 V 60 www Wwwww 30 X www 302 Cell B 2 2 A 4 Zero 2 2 A 4 Zero 2 12 V www 502 50 EARTHING OR GROUNDING IN AN ELECTRICAL CIRCUIT

16 www 1923 192 SV sir yha pe Eeq tential difference B answer kaise hai yha pe internal resistance ke ross koi potential Top nhi hoga kya 202 2V Find out potential difference between point A and B 1 3 5 V 3 4 V 46 A www Eat 202 E 5V 302 www 2 3 V 4 5 V 2V 30 E E 11 rr 5 2 3 3 3 5V 11 3 3 B 129

A B C In the circuit shown the device D has a property that if initially non conducting it remain conducting until voltage across it rises to a value V V It then rapidly discharges the until the voltage across it drops to a negligibly small value where upon it returns to a non state The volatage developed across the capacitor is Periodic with time period RC Periodic with time period RC In Penodic with time period RC In V V V