Current Electricity Questions and Answers

33 Two identical bulbs are connected in parallel across an ideal source of emf E The ammeter A and voltmeter Vare ideal If bulb B gets fused then Sir A B B E 1 Reading of A will increase but that of Vwill remain same 2 Reading of A will decrease but that of V will increase 3 Reading of A will decrease but that of V will remain same 4 Reading of A will increase and reading of V will also increase

11 In the circuit shown in figure if ammeter and voltmeter are ideal then the power consumed in 902 resistor will be A 2002 1 3 33 W 3 144 W 902 We www 102 www 3002 622 V 30V 2 4 W 4 500 W N 2

mm s 1 Average collision time for electrons conductor under a certain pote difference is found to be 10 15 s The mob of electron in metal conductor is NCERT Pg 1 1 5 x 10 3 m V s 2 2 2 x 10 3 m V s 3 2 9 x 10 3 m V s 1 75 x 10 4 m V s

charged particle is having drift veld 5 x 104 m s1 in an electric fi 10 V m 1 The electron mobility NCERT P 2 5 x 104 m V 1 s 1 2 5 x 105 m V 1 s 1 2 25 x 10 13 m V 1 s 1 4 1 10 m V 1 s 1

Thousand cells of same emf E and same internal resistance r are connected in series in same order without an external resistance The potential drop across 399 cells is found to be 1 Zero 3 601 E 2 399 E 4 1000 E

A current of 10 A is maintained in a conductor of cross section 1 cm2 If the number density of free electrons be 9 1028 m 3 the drift velocity of free electrons is 1 6 94 x 10 6 m s 3 1 94 x 10 m s 2 5 94 x 10 m s 4 2 94 x 10 4 m s

8 The resistance of a rectangular block of copper of dimensions 2 mm x 2 mm x 5 m between two square faces is 0 02 22 What is the resistivity of copper 1 1 6 10 89 3 1 6 10 8 9 m 2 1 6 10 6 22 m 4 Zero

9 Ends A and B are connected to positive and negative terminals of a cell of emf 12 V respectively The value of voltage shown by voltmeter of negligible resistance is A 1 Zero 3 6 1 62 62 62 62 www www www www V 2 3 V 4 12 V

4 In the situation shown in figure an ideal ammeter is connected across 72 resistors Select the correct statement from the following 2 22 www A 72 www 10 V 14 12 1 The current drawn by the battery is 1 A 2 The currents through 2 2 and 7 are equal 3 The rate of heat production in 7 2 is less than that in 2 Q 4 Roth 1 2

49 Two electric bulbs whose resistance are in the ratio of 1 2 are connected in parallel to a constant voltage source The power dissipated in them has the ratio 1 2 1 3 1 4 2 1 1 4 1 2 60 1

4 A voltmeter is connected in parallel with a variable resistance R which is in series with an ammeter and a cell as shown in the figure For one value of R the meters read 0 3 A and 0 9 V For another value of R the readings are 0 25 A and 1 0 V What is the internal resistance of the cell F 1 0 5 Q 2 2 Q 3 1 2 Q G WWR

37 In figure the e m f of the cell is 2V and internal resistance is negligible The resistance of the voltmeter is 80 ohm The reading of the voltmeter will be www 20 Q 1 2 volt 3 1 60 volt 2 V F V 809 802 2 1 33 volt 4 0 80 volt

A curved rectangular bar forms a resistor the curved sides are concentric circular arcs If p is the resistivity of the material of bar I is the length of inner arc of radius ro r b is the radius of the outer arc and a is the width of the bar Find resistance of bar across its rectangular ends dr 0 b b a

the circuit shown in the figure the switch was kept in position 1 for a very long time and then at t 0 it is shifted to position 2 The current in the rcuit immediately after that is i A then the value of a b is b 2 ellee S 10 H 5 H moooo www 1022 40 V

1 3 flux flux time time 2 4 10 V 292 wwwww flux flux 302 time B time In the circuit shown in the figure the magnitude of potential difference between point A and Eis 42 4 V 3 191 An imaginary cube of edge length is shown in th figure A uniformly charged rod having linear charg density 2 and length L moves towards left wi constant speed v At time 0 the left end ju touches the centre of face of the cube D Choose the correct graph which represents the flu of the electric field through the cube as rod goe through it ww 332 www 352 wwww 352 www v constant 302 10 V 65 E

9 The equivalent resistance between A and B in the given network is 19 292 www wwwww 19 19 wwww 19 wwwww 292 K wwww 19 B A 1 3Q 2 20 3 10 Q 4 5 Q Each of the ropintongo in the network given below 14

A bipolar junction transistor with one junction forward biased and either the collector or emitter open operates in the a cut off region b saturation region c pinch off region d active region

i A magnetic flux through a stationary loop with a resistance R varies during the time interval t as at t 1 Find the amount of heat generated in the loop during that time The inductance of the loop is to be neglected

7 Ten cells of emf 1 5V and internal resistance 1 2 are connected across a R2 resistor i All In series ii All in parallel Find the expressions for power dissipated in the resistor R in each case For what values of R the powe in case ii is more

9 Three cells of emf 5V and 10 V and 15 V have internal resistances 202 each The cells are connected in series with an external resistance R and the polarity of the 1st cell opposing those of the other two Find R if the terminal voltage across the 1st battery is 7 5 V 0 Find the equivalent resistance between A and B if each resistor has a A ww

76 A simple potentiometer circuit is shown in figure The internal resistance of 4 V battery is negligible AC is the uniform wire of length 100 cm and resistance 2 9 What would be the length of AB for which galvanometer shows zero deflection 1 82 5 cm 3 165 cm A 4 V H 1 5 V 2 4 2 www B G C 2 41 50 cm 4 50 cm

49 Four identical cells each having emf E and internal resistance r are connected in series to form a loop ABCD as shown in figure Find potential difference across AB and AC A www E U B E

A part of circuit is shown in figure The wire A is a very thick copper and wire B and C are identical wires of manganin The currents in wires A B C will be respectively A 1 1A 1 A 2 A 2A 2 0 2 A 2 A www B wwww C 3 2 A 0 2 A 4 2 A 2 A 2 A

Current Electricity 63 A battery of 12 V and an internal resistance of 0 8 9 is connected to 3 resistors as shown in the figure The current in the circuit is 1 2 3 A 2 4 0 A 49 www 0 89 www 20 wwww www 39 12 V 3 2 0 A 4 1 33 A

as shown in the figure the potential difference across the resistance 2 R is the cell has emf E volt and no internal resistance 4 R www www R www 19 2 R

74 An unknown resistance R is connected in series with resistance 109 When the combination is connected to left gap of a metre bridge and R is connected to right gap balance point from left end is at 50 cm When the 10 Q is removed the balance point shifts to 40 cm The value of R is 1 200 3 60 Q 2 10 Q 4 40 Q

4R 3 62 Two batteries of emf 4 V and 8 V having the internal resistance of 1 92 and 2 2 respectively are connected in circuit with a resistance of 9 52 as shown in figure The current and potential difference between the points P and Q are 1 1 12 A and 12 V P 2 192 4 V A and 9 V www 92 8 V 3 www 292 1 6 be in the ratio R A and 4 V 4 1 3 or 3 4 A and 3 V

tour times the original value Masses of three wires of copper are in the ratio of 1 3 5 and their lengths are in the rat of 5 3 1 The ratio of their electrical resistance is 1 125 15 1 2 1 15 125 3 5 3 1 4 1 3 5

Multiple Choice Questions I A constant current I flows in a strip line conductor resistivity of which resistivities at cross sections A and B are PA and PB find excess charge increases monotonically in the direction of the current flow If relative permittivity of material of the strip is everywhere in the strip accumulated in the section AB Permittivity of free space is and a PB PA I c 1 PB PA I b PB PA I d 1 PB PA I A

In the circuit as shown in the figure the value of resistance Ris ay my t 1 A 25 VT R www OPTIONS CLEAR SELECTION A 220 B 210 C 250 90 90 90 MARK FOR REVIEW

A parallel combination of following cells is to an external load If all the cells are connected connected in same polarity then the value of resistance of the external load such that the power transfer to the load is maximum is S No EMF Internal Resistance 1 2 3 4V 40 6 V 40 2 V 20 030 020 040 012

Sir in a conductor with a battery connected to it would have electric field within it which would help electrons to accelerate than why we say they have constant drift velocity can u plz explain this concept NPK DOUBTS 10 51 PM x

In a gas discharge tube if 1 25 into 10 to the power 16 electrons are flowing per second from left to right and 1 25 into 10 to the power 16 protons are flowing per second from right to left in a gross given cross section in then calculate the strength of the current and also find its direction SHARE B 0 Follow 2

Kq surface of shell is 2R2 before closing the switch S The electric potential at the centre C due to charges on the outer surface of shell Kq R before closing the switch S is The electric potential at the centre C due to charges on the outer surface Kq R after closing the of shell is switch S Charge flown through the switch into

Two cells each of emf E but internal resistance f and r are connected as shown in figure If potential difference across second cell is zero then value of Ris 1 1 R E 2 1 1 4 r r

150 kn and Problem 8 Consider the circuit of Fig 14 6 2 with Vs 100 V R R2 50 kn Suppose the voltage across R is measured by using the 0 50 V scale of a voltmeter having sensitivity 20 kn V Calculate the percentage error in measurement due to loading effect of the voltmeter

3 remain constant 4 become zero Masses of 3 wires of same metal are in the ratio 22 1 2 3 and their lengths are in the ratio 3 2 1 The electrical resistances are in ratio 1 1 4 9 2 9 4 1 3 1 2 3 4 27 6 1 A ring is made of a wire having a resistance R 12 2 Find the points A and B H 23 3 fed eft 4 treffend 23 21 3 1 1 4 9 2 9 4 1 3 1 2 3 4 27 6 1 R 12 12

Problem 6 The deflection system in a CRT employs a magnetic field of 10 4 T acting over an axial length of 3 cm and is placed 20 cm from the screen If the accelerating voltage is 800 V find the deflection of spot on the fluorescent screen Also calculate the deflection for an ion of charge same as that of an electron and of mass 1600 times the mass of an electron

72 What is the current through the resistor R in the circuit given below E 10V r 122 H A 2 A E R3 R ww R 5A 3A P 3R 52 te

When Shunt of 402 is attached to a galvanometer 7 the deflection in the galvanometer is reduced to 1 5th If an additional shunt of 20 is also connected the deflection of galvanometer will be reduced to 1 2 th of initial 10 1 13 th of initial 3 Remains the same 4 None of these eder a ted fter fazdy Ja to small 4 20 44 5 Gaeder an fact fandel 1 S 1 2 3 TEAT 4

na certain series LCR A C circuit it is found that X 2Xc and phase difference between the current and voltage is 4 how capacitance is made 1 4th the inductance and resistance are doubled then which are not correct Voltage will lead current by a phase of tan 1 2 Voltage will lag behind current by a phase of tan 1 2 Voltage will lag behind current by a phase of 4 Voltage and current will be in same phase

Find potential at point X in given circuit 2 3 10 V 10 V 1V 9v Correct Answer 2 Status unattempted Add to Bookmark List 202 40 40 302 IN IN X 6V w 202 13V

Rated powers of bulbs are shown in the figure The 24 W and 48 W bulbs have a tolerance that they can work without blowing till they consumes 10 more than rated power Both the 72 W bulbs have a tolerance of 20 higher than rated power What is the maximum power in W the combination of bulbs can consume without any bulb blowing off 24W 60 72W 292 48W 302 72 W 292

snown connected between points A and B then the current in this wire will 3Q www www 19 B A V 292 ww 392 1 Flow from A to B 2 Flow from B to A 3 Not flow 4 Flow in the direction which will be decided b

Example 59 Find in the given network of resistors the equivalent resistance between the points A and B between A and D and between A and C IIT Solution The resistors AD 392 and DC 792 are in series to give a total resistance R 10 Q2 The resistance R 102 and the resistor AC 1022 are in parallel Their equi 30 D A 79 W 10 92 w 10 22 Fig 2 20 C 592 B

In the adjoining circuit diagram each resistance 6 is of 10 2 The current in the arm AD will be 2i 1 2 1 3 4i 5 D 3i When Shunt of 40 is attached to a galvanometer 7 AD 1 3 15 2 ZA 4 35115 10 Q2 yo 5 4 er rart at

connected connected to an external load If all the cells are in same polarity then the value of resistance of the external load such that the power transfer to the load is maximum is S No EMF Internal Resistance 1 2 3 4 V 4Q 6 V 4Q 2 V 20 3Q 20 040 10

Figure shows a set of equipotential surface An electron is being moved from one point to other 40 V 20 V 30 V B 144 0 A Work done by the electric field in moving the electron 1 From A to B is more than from B to C 2 From A to B is less than from B to C 3 From A to B and from B to C are zero 4 From A to B is same as from B to C

In the circuit element given here if the potential B at point B V 0 then the potentials of A and D are given as 1 502 2 502 wwwww A B lamp 2V co ALLEN 41 1 VA 1 5 V V 2V 2 V 1 5 V V 2V

A conducting rod is moving with a constant velocity v over the parallel conducting rails which are connected at the ends through a resistor R and capacitor C as shown in the figure Magnetic field B is into the plane Consider the following statements X E R X X X L X B X X X H EC X 1 Current in loop AEFBA is clockwise ii Current in loop AHGBA is clockwise iii Current through the capacitor is zero iv Energy stored in the capacitor is CB L v Which of the following options is most suitable A Statements 1 and iii are correct B Statements ii and iv are correct C Statements ii iii and iv are correct D None of these