Current Electricity Questions and Answers

A set of n equal resistors of value R each are connected in series to a battery of emf E and internal resistance R The current drawn is Now the n resistors are connected in parallel to the same battery Then the current drawn from battery becomes 10 The value of n is NEET 2018 2 11 4 20 1 10 3 9 umber n of

A potentiometer wire has length 4 m and resistance 8 Q 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 48 Q 32 Q 02 48 hr min O 40 Q

power 3 ohm m Current density is given as OPTIONS 4 31 X 10 power 8 A m2 6 31 X 10 power 6 A m2 710 03

steady current e wire is 4 V x 20 cm is 20 V 100 cm For circuit shown in figure the current must not exceed A B 1 1 mA 3 5 mA 1 4 W www 250 K 1 4 W www 10 KQ 1 W www 10 KQ 2 2 mA 4 10 mA

ay Forward In the following circuit the potential difference between A and B VB VA is A R 2A wwww 15 V 1 10 V 3 15 V B 592 2 5 V 4 7 5 V r 19 www Potential difference across the terminals of th battery shown in the figure is r 122 shown i the figure is internal resistance of the battery 10 V

In the absence of electric field possible path of free electrons inside a conductor between consecutive collision is NCERT Pg 100 1 Hyperbolic 3 Parabolic 2 Straight line 4 Elliptical

R R R R E In the above network R 2 2 and E 12 V The equivalent resistance of the above netwo and current through each branch of the network is a 4 2 and 2 5 A respectively b 2 2 and 3 A respectively c 2 2 and 6 A respectively d None of the above

of radius R t The initial rical region is 2A s 9 If current in an electric bulb is decreased by 25 then how will power in the bulb change 1 50 2 56 25 3 36

Electrical power is transmitted from power stations to different places via transmission cables at very high voltage to for Minimize power loss during transmission Safety of people Maximize power loss during transmission Both 2 and 3

A piece of wire of resistance R is cut into five equal parts These parts are then connected in parallel The new resistance of this combination is R then the ratio R R is 25 x Here x is 625

In a potentiometer circuit the balancing length of resistance wire for cell of electromotiv force E and negligible internal resistance is L If one more cell of same electromotive force and negligible internal resistance is joined in parallel to the cell of electromotive force E new balancing length will be faccuf infaad ag an E un cuve siafer afar u na y gfaa za in foren fer algeh am E aun auwe eiaf FREE ufdriem areas L uld a g4

An electrical circuit is shown in the figure Calculate the potential difference across the resistance 00 ohm as will be measured by the voltmeter V of resistance 400 ohm either by applying Kirchhoff ules or otherwise 10002 www www 10002 10002 www 40002 www 20002 www

2 3 6 LIMITATIONS OF OHM S LAW Although Ohm s law has been found valid over a large class of materials there do exist materials and devices used in electric circuits where the proportionality of V and I does not hold The deviations broadly are one or more of the following types a V ceases to be proportional to I Fig 3 5 b The relation between Vand I depends on the sign of V In other words if I is the current for a certain V then reversing the direction of V keeping its magnitude fixed does not produce a current of the same magnitude as I in the opposite direction Fig 3 6 This happens for example in a diode which we will study in Chapter 14 semiconductor 1 5 mA I LA 0 2 V Board Question FIGURE 3 6 Characteristic curve of a diode Note the different scales for negative and positive lues of the voltage and current Current I mA I FIGURE 3 5 The dashed line represents the linear Ohm s law The solid line is the voltage V versus current I for a good conductor IMP Negative Non linear resistance region region Voltage V V FIGURE 3 7 Variation of current versus voltage for GaAs

A carbon resistor has coloured strips as brown green Orange and silver respectively The values of resistance S O 15 KQ 10 15 KQ 5 15 KQ 20 O 10 KQ 5

re than t and some less than t In other words the time t in 5 will be less than t for some and more than t for others as we go N The average value of t then is t the values of i 1 2 as relaxation time Thus averaging Eq 3 16 over the ons at any given time t gives us for the average velocity v V average v average eE m e E m T eE 3 17 This last result is surprising It tells us that the electrons move with an average velocity which is independent of time although electrons are accelerated This is the phenomenon of drift and the m t average T

In the circuit shown the instruments are ideal Then readings of ammeter and voltmeter s are B 4 92 ww Only one correct answer A 1 A 10 V C A D 2 A 20 V 3 A 30 V 4 A 40 V 1022 Wwwww 30 V 1502 www 30 192

EMF of a cell is potential difference across the terminals of the cell when they are a open b externally connected by a wire c internally connected by a wire d either a or b 1 Point Option a Option b Option c

10 A parallel plate capacitor is charged to 60 C The plate losses charge at the rate of 1 8x10 8 Cs The magnitude of displacement current is 1 1 8x10 Cs 1 3 4 1x10 11 Cs 1 11 A plane electromagnetic 2 3 6x10 Cs 1 4 5 7x10 12 Cs wave propagating in the x 16

Q 11 SUBJECTIVE NUMERICAL Three monochromatic sources having wavelengths 12 42 nm 6 21 nm and 24 84 nm are placed close to each other in front of a converging lens such that equal powers from the three equal to 1 mW each fall on a converging lens and then on a small spherical conductor of radius r 1 cm and work function 62 1 eV Assume 50 efficiency of emission and no change in effective value of work function due to photoelectric emission and potential rise Use hc 1242 eV nm all electrons emitted by the sphere are immediately removed by some non electrical mechanism At t 8 s switch S is closed so that the sphere gets connected to the earth via resistor of value 6 75 MQ Find the current in A flowing just after the switch is closed af 12 42 nm 6 21 nm 24 84 m a pequffu atat c yg ffu u mg Chat Act 34 Uhr zu Ga 1 mWz a vu da uz ufa r 1 cm 62 1 eV yg ott nu ma a 50 faya fa am faua df ku hd da urada as stai hc 1242 M Gu 3Afa A V nm fe ufaydu Mu faw ge si suu S3 cl a 2 G 6 75 M qe au a 31 J141 Rda ch are the di gara sta A A S D S ufaduh ha ch R www Ground RT

An accumulator of 4 V is connected through a resistance of 30 2 to a potentiometer wire 10 m long and of resistance 30 2 When a cell is connected through a galvanometer to the potentiometer the null point is found at 5 5 m from the common terminal The potential gradient in the wire is 1 A V m 15 5 V m B D 1 10 3 V m V m

3 The length of a given cylindrical wire is increased by 100 Due to the consequent decrease in diamete the change in the resistance of the wire will be 100 a uchachicht als 1 300 2 200 3 100 4 50

A potentiometer wire of length 1 m and resistance 10 2 is connected in series with a cell of e m f 2 V with internal resistance 1 and a resistance box including a resistance R If potential difference between the ends of the wire is 1 mV the value of Ris A 20000 S C 10000 S LOBY D 19989 Q 9989 S

77 Two cells with the same emf E and different internal resistances r1 and r2 r are connected in series to an external resistance R The value of R so that the potential difference across the first cell be zero is a 7 E E Jon 11 12 b 1 12 1 1 2 2 d M

75 The length of a wire of a potentiometer is 100 cm and the emf of its cell is E volt It is employed to measure the emf of a battery whose internal resistance is 0 5 Q2 If the balance point is obtained at 1 30 cm from the positive end the emf of the battery is 30E a b c d 100 5 30E 100 0 5 30 E 0 5i where i is the current in the potentiometer 9 100 wire 30E 100

Four resistances arranged to form a Wheatstone network are 8 12 Q2 6 2 and 27 Q2 The resistance should be shunted across 27 so that the bridge is balanced is resistance A 13 5 C 13 Q B D 14 5 Q 14 Q

Note Each question carries 5 Marks Question 1 Find the equivalent resistanc between terminals A and B Where R1 1170 R2 1562 R3 312 2 R4 1560 R5 11 2 R6 780 and R7 39 22 A R www R R un R5

A charged capacitor C 3 F is getting discharged in the circuit shown When the current I was observed to be 2 5A switch S was opened Determine the amount of heat in uJ that will be liberated in the circuit after S is opened C 3 F I www S C 2 F HH

95 Two batteries of emf and 2 2 and internal resistances and 2 respectively are connected in parallel as shown in figure NCERT Exemplar 1 A HH 82 11 www 12 B a Two equivalent emf q of the two cells is between and 2 i e Eeq b The equivalent emf q is smaller than c The q is given by q 2 always is independent of internal resistances and ra

2 In a metre bridge figure below the null point is found at a distance of 33 7 cm from A If now a resistance of 12 ohm is connected in parallel with S the null point occurs at 51 9 cm Determine the value of R and S DF B 100 C

3 80 cm 4 60 cm 22 In the given circuit the heat developed across 60 resistor in 2s will be 23 1 32 3 3 24J ap www 30 20V 602 www www 302 50 16 2 J 4 40J the radius of cross section of a conductor ise

19 Using Kirchhoff s rules determine the value of unknown resistance R in the circuit Fig 2 62 so that no current flows through 40 resistance Also find the potential differ ence between A and D F A 12 10 9 V IE www 40 T6V 3V I B Fig 2 62 IC R 20 3 V

4 go 71 A current of 4A flows in a coil when connected to a 12V DC source If the same coil is connected to a 132V 50rad s AC source a current of 2 4A flows in the circuit Determine the inductance L of the coil Aslo find the power P developed in the circuit if a 2500 F capacitor is connected in series with the coil AL 0 08H P 17 28W 2 L 0 16H P 17 28W 3 L 0 08H P 8 64W A

When no current is passed through a conductor A B C D The free electrons do not move The average speed of a free electron over a large period of time is zero The average velocity of a free electron over a large period of time is zero The average of square of velocities of all the free electrons at an instant is zero

92 A battery has six cells in series Each has an emf 1 5V and internal resistance 1 ohm If an external load of 24 22 is connected to it The potential drop across the load is 1 7 2V 2 0 3V 3 6 8V 4 0 4V

88 A voltmeter of resistance 99 22 connected across a cell shows a reading of 9 9V An ammeter of resistance 12 connected to the same cell shows 5A The emf of the cell is 1 9 9V 2 14 9V 3 10V 4 9 8V

35 The pd a cross terminals of a cell is found to be 29 volt and 28 volt respectively when it delivers a current of 1 ampere and 2 ampere respectively The emf and internal resistance of a cell are respectively 1 30V 292 3 29V 192 2 30V 122 4 28V 20

A toaster has a heating element which has a temperature coefficient of resistivity of 2 0 x 10 3 C The toaster is plugged into an outlet which delivers a constant voltage If the resistance of the wire did not change with temperature the toaster would be able to coast a piece of bread at 22 C in 26 s If the toaster reaches a temperature of 250 C how long does it actually take to toast the same Diece of bread

An apparatus is connected to an ideal battery as shown in figure For what value of current power delivered to the apparatus apparatus 2 33 3 ERE ES 2R 4R information is insufficient

Read More For a cell a graph is plotted between the potential difference Vacross the terminals of the cell and the current drawn from the cell The emf and internal resistance of the cell is E and r respectively V volt 2 1 5 1 0 5 1 2 3 4 5 amp E 2 V r 0 5 Q O E 2 V r 0 40

A zener diode having breakdown voltage equa to 15 V is used in a voltage regulator circui shown in figure The current through the zene diode is 1 5 mA 25092 wwwww 15V 1kQ 2 10 mA

In the electrical circuit shown in figure the 35 current through the 412 resistor is www 22 9V 1 1A 3 0 25 A www 302 202 www 802 252 www 2 0 5 A 4 0 1 A www 4023 fax far aga 4 and are un ZH 9V 1 I for 3 0 25 ofert www 352 202 802 www www 202 402 202 www 2 0 5 m 4 01 fe

14 In the circuit shown below what will be the reading of voltmeter V and ammeter A vodovod 300V 1 200V 1A 3 220V 2A 300V 10092 V 220V 50Hz 2 800V 2A 4 220V 2 2A

o Zero Four ammeters with identical internal resistances r and a resistor of resistance R are connected to a current source as shown in figure It is known that the reading of the ammeter A is l 3 A and the reading of the ammeter A2 is l2 5 A Determine the ratio of the resistances R r A A A A3 R

4 All of these QA 2 t The graph between charge Q in coulomb a t in second is parabolic The average currer interval 0 to 4 second is 1 2 amp 3 16 amp 2 1 amp 4 4 amp

The figure below shows a U tube attachet its ends to two glass bulbs one coated black paint and the other polished The tub partly filled with alcohol When a 100 bulb is placed between the glass bulbs X Painted Black Alcohol Painted White A the level of alcohol in X falls while t in Y rises B level of alcohol in X rises while that of falls C the level falls in both D there is no change in the levels of alcoh

Pick out the correct statement from the following A B C D Charge flows slower where the conductor is smaller in cross section Charge flows faster where the conductor is larger in cross section Whatever be the cross section charge flow rate remains unchanged Both charge flow and flow rate depend upon the cross section of the conductor Correct Answ Your Answ

In the circuit shown in figure B 492 F Read More 2 V E 492 2 V HH 2 V O Current in wire AF is 1 A O Current in wire CD is 1 A www p O Current in wire BE is 2 A O Current in wire AB is zero 492

A battery of emt E is connected across a conductor as shown As one observers from A to B B A r E Column I i Current ii Drift velocity of electron iii Electric field iv Potential drop per unit length r2 Column II 1 i p ii q iii r iv s 2 i r ii q iii q iv q 2 i ii niii int p increases q decreases r remains same s cannot be determined Now match the given columns and select the correct option from the codes given below Codes

A battery of 6 volts is connected to the terminals of a three metre long wire of uniform thickness and resistance of the order of 100 2 The difference of potential between two points separated by 50 cm on the wire will 1 1 V 3 2 V 2 1 5 V 4 3 V

A network shown in the figure consists of a battery and five unknown resistors When a ideal ammeter is connected between the terminals A and B its reading is 4 A and when a resistance of 3 is connected in series with the ammeter its reading becomes 2 A Now the ammeter and the resistance are disconnected and an ideal voltmeter is connected between the terminals A and B What would the voltmeter read A mm Bq till