Current Electricity Questions and Answers

In a meter bridge experiment null point is obtained at 40 cm from one end of the wire when resistance X is balanced against another resistance Y If X Y then the new position of the null points from the same end if one decides to balance a resistance of 3X against Y will be close to

c 10 A d 10 A 79 A npn transistor is connected in common emitter configuration in a given amplifier A load resistance of 800 2 is connected in the collector circuit and the voltage drop across it is 0 8 V If the current amplification factor is 0 96 and the input resistance of the circuit is 19202 the voltage gain and the power gain of the amplifier will respectively be 2016 a 4 3 84 c 4 4 b 3 69 3 84 d 4 3 69

A potential difference of 250 V is applied to a metallic wire at 15 C when a current of 5 A was flowing What wil be temperature of wire when current has fallen to 3 9 A and applied voltage being constant 21 15 C 1 2 dav 72 C 87 C 105 C 312 C

A wire of resistance 10 0 ohm is stretched and increases its length by 20 Its resistance then would be Neglect any change in volume or resistivity A 10 0 ohm B 12 0 ohm C 14 4 ohm D 10 2 ohm Figure shows a copper wire of nonuniform cross section carrying current toward right for sectors A B and C

175 If in a p n junction a square input signal of 10 V is applied as shown then the output across R will be 2015 a c 5V A 5V 10Vr n 5V 0 b d RL T 5V 10V O 178 179

6 A conductor with rectangular cross section has dimensions ax 2a x 4a as shown in figure Resistance across AB is x across CD is y and across EF is z Then A x y z A B x y z E 4a D a C y x z B D x z y

If the voltage across a 25 2 resistor is v 50 sin 500t 75 which of the following is the expression for the resistor current O2 sin 20t 3 O2 cos 500t 75 O1250 sin 500t 75 O2 sin 500t 75

In a metre bridge circuit as shown when one more resistance of 100 Q is connected in parallel with unknown 4 resistance X then ratio becomes equal to 2 where 12 is balancing length shown from end A AB is a wire with uniform cross section Then value of X is ww www 100 S A 400 Q 100 Q 50 Q 300 0 35 ww

Figure shows a copper wire of nonuniform cross section carrying current toward right for sectors A B and C E A i i i i current C V V V V drift velocity B E E E E electric field D J J J J current density

A wire of resistance 4 Q is used to wind a coil of radius 7 cm The wire has cross sectional diameter of 1 4 mm and specific resistance of its material is 2 x 10 70 m The number of turns in the coil is 10 30 50

48 A wire of a certain material is stretched slowly by ten percent Its new resistance and specific resistance become respectively 2008 a 1 1 times 1 1 times c 1 21 times same b 1 2 times 1 1 times d Both remain the same

17 Problem 5 Consider the circuit in the diagram with sources of emf listed below Randomized Variables 28 V 43 V 43 3 5V 44 31 V 33 Part a Find I in amps 33 Part b Find I in amps 5 0 A 78 11 i 4 0 100 0500 10 050 h 40 2 P 2012 4 20 200

This question contains Statement 1 and Statement 2 Of the four choices given after the statements choose the one that best describes the two statements STATEMENT 1 For a mass M kept at the centre of a cube of side a the flux of gravitational field passing through its sides is 4 TGM STATEMENT 2 If the direction of a field due to a point source is radial and its dependence on the distance r from the source is given as r2 its flux through a closed surface depends only on the strength of the source enclosed by the surface and not on the size or shape of the surface B Statement 1 is True Statement 2 is True Statement 2 is not a correct explanation for Statement 1 Statement 1 is True Statement 2 is False QU 1 6

In the circuit shown in the figure the magnitude of potential difference between point A and E is 202 10 V 302 1 27 V 3 17 V A ted 492 4 V D dations 2 21 V 4 24 V 352 www 302 www 3922 wwwww 352 10 V www 60 E

Figure shows a balanced Wheatstone s bridge S 102 B P 100 S2 A R 5Q Q 50 Q C 4100 A If P is slightly increased the current in the galvanometer flows from C to A B If P is slightly increased the current in the galvanometer flows from A to C C If Q is slightly increased the current in the galvanometer flows from C to A D If Q is slightly increased the current in the galvanometer flows from A to C Which of the above options is are correct 1 A B 2 B C 3 C D 4 A D

Two batteries A and Bare connected in parallel and a resistance R 10 Q is connected across their terminals A has emf of 12 and internal of 2 Q Bhas emf of 8 V and internal of 1 Q The potential drop across 10 resistance resistance resistor is 6 75 V 9 V 8 75 V 10 5 V A WWWWW www B www R 100

Two non ideal batteries of emf and 2 2 are connected in parallel Then A Equivalent emf is larger than greater emf B Equivalent internal resistance is larger than either of two internal resistance Both of A and B are correct Both of A and B are incorrect A is correct and B is incorrect A is incorrect and B is correct

Five identical resistors marked a b c d and e are connected in a circuit as shown in the figure The ratio of power dissipated through b to the power dissipated through c is b 4 1 2 1 4 3 a d

Two resistors of value 1 kQ and 4 kQ are connected in series across a constant voltage supply of 100 V Now a voltmeter having internal resistance of 12 kQ is connected across 4 ko resistor What will be increase in current supply from source 2 5 mA 4 mA 10 mA

Consider a synchronous generator connected to an infinite bus by two identical parallel transmission lines Constant mechanical input of 1 pu The transient reactance x of the generator 0 1 pu Due to some previous disturbance the rotor angle d is undergoing an undamped oscillation with the maximum value of 8 t equal to 130 One of the parallel lines trip due to relay mol operation at an instant when 8 t 130 as shown in the figure The maximum value of the per unit reactance x such that the system does not lose synchronism subsequent to this tripping is 1 0 8 x 0 1pu ww www 1 0 0

The incorrect statement among the followings S For some high resistance alloys like manganin increase in resistance with temperature change is negligible Insulators like rubber and glass are said to possess negative temperature coefficient of resistance For most of metals increase in resistance with temperature rise is fairly regular for normal range of temperature Generally resistivity of any alloy is equal to resistivity of its constituent elements

22 For the arrangement shown in figure the charge on the 10 F capacitor is 4 F 11 10 V 10 F 20 V 1 300 C 2 200 C 3 100 C 4 Zero Charge Qon capacitor vorig juille 10 V

The circuit shown in the diagram extends to the right into infinity Each battery has the electromotive force V unknown and the internal resistance r known Each resistor has the resistance 4r The reading of the ideal ammeter shown in the diagram is I Find the value of V in terms of I and r 4r 4r 4r IV IV r IV r OV 2 2 2 Ir OV 2 2 2 Ir OV 4 5 Ir OV3 0 Ir

A current is flowing through a cylindrical conductor of radius R such that current density at any cross section is given by J J 1 F where r is radial distance from axis of the cylinder R Calculate the total current through the cross section of the conductor

n a metre bridge circuit as shown when one more resistance of 100 Q is connected in parallel with unknown resistance X then ratio becomes equal t 2 where is balancing length shown from end A AB is a wire with uniform cross section Then value of X is www X A wwww 100 Q 400 Q 100 Q 50 Q 4 F 12 ww B

In the circuit shown the value of R in ohm such that there will be no current through 30 V battery is R 30 V 20 Q 30 Q 40 Q 50 V 2002

When the key kis pressed at time t 0 then which of the following statements about the current in the resistor AB of resistance 1 kQ of the given circuit is true 2 V 1 kQ Felele 1 mH A B 1 kg oscillates between 1 mA and 2 mA 1 mA at all t At t 0 1 mA and with time mA goes to 2 At t 0 1 0 and with time it goes to 1 mA

With increase in frequency of an a c supply the impedance of an LCR series circuit 1 Remains constant 2 Decreases 3 Increases 4 Decreases at first becomes minimum and then increases

A B and C bulbs are connected in circuit as shown in diagram B and C are of same type and if bulb C is fused then in comparison to the earlier case A B C D A Q B C Q A and B both will glow more A and B both will glow less A will glow less while B will glow more None of bulb will glow

An inductor designed with 400 turns coil wound on an iron core of 16 cm cross sectional area and with a cut of an air gap length of 1 mm The coil is connected to a 230 V 50 Hz ac supply Neglect coil resistance core loss iron reluctance and leakage inductance o 4 x 10 7 H M The average force on the core to reduce the air gap will be

A technician has only two resistance coils By using them singly in series or in parallel he is able to obtain the resistance 3 4 12 and 16 ohms The resistance of the two coils are 1 6 and 10 ohms 3 7 and 9 ohms 2 4 and 12 ohms 4 4 and 16 ohms

A 33 KVA 2200 220 V 50 Hz single phase transformer has the following parameters Primary winding h v side resistance r 2 4 2 Leakage reactance x 6 002 Secondary winding 1 v side resistance r 0 03 2 Leakage reactance x 0 07 2 The total ohmic loss of the transformer at full load will be a 1216 watts b 1205 watts c 1175 watts d 1605 watts 707

A 500 KVA 440 V synchronous generator is supplying a passive load of 400 kW at 0 8 lagging power factor It has a sub transient reactance of 0 1 pu What is the value of post fault current at generator terminals 1 6 97 KA

40 Current Electricity 36 The equivalent resistance between A and B in the following network is R 1 R A www 2R wwwwww 2R wwww R 2 www R 7R 5 B

e In given figure if R 30 R 60 R3 90 emf 18V then find currect i through R just after the switch is closed e 18V 1 0 A i 2 3 A 3 6 A 2mH elle w Question Type Single Correct Type 1 R 2mH elle R 5 mF

20 The effective resistance in the given circuit between A and B points is 12 Awwwwwwwww B 1 20 3 8 w 00 29 www a 3 19 www www 10 2 10 2Q 4 322 1 Figure shows a portion of a circuit Value of current through R is

A series circuit contains a resistance R a capacitor CF a coil L H supplied by a 1 c source with e m f EV Derive an expression for the current in the circuit for critica lamping condition The initial current i 0 A and the capacitor voltage vc 0 V i If the source e m f 25 V coil inductance is 600 mH and the capacitor is 200 mF what is the voltage across the capacitor at t 1 0 s Hints 1 use KVL to write equation v VR VC E 2 make use of v Li VR Ri vc q C and i q to write differential equation in terms of q 3 remember for critical damping the C F y A Bt e because 0 4 the value of R can be found for critical damping condition from L and C

In the given circuit diagram when the current reaches steady state in the circuit the charge on the capacitor of capacitance C will be 2 CE 1 1 3 CE 5 r 1 r 4 CE E www 11 HIWWW C www 12

S B E In producing chlorine by electrolysis 100 kW power How much chlorine at 125 V is being consumed per minute is liberated E C E of chlorine is 0 367 2010 Pre 10 6 kg C a 3 67 10 kg c 9 67 10 kg Consider the following two statements b 1 76 10 kg d 17 61 10 kg X complete circle 10 cm The resista its two diametric points A and B a a 3 02 b 6 43 See the electric of the following

Four identical resistors each of resistance 2 2 are connected to battery of 20 V and internal resistance 22 as given below The reading of ideal ammeter A and A are 22 22 29 22 A 20 V T 22 1 8 A 8 A 3 10 A 10 A A 2 5 A 5 A 4 4 A 4 A

A dc source of emf E 100 V and internal resistance r 0 502 a storage battery of emf E 90 V and an external resistance R are connected as shown in figure For what value of R no current will pass through the battery 1 5 5 2 3 4 5 2 2 3 50 4 2 5 S E Hill Hill E www R r 0 50 www

A 10 V battery with internal resistance 12 and a 15 V battery with internal resistance 0 6 2 are connected in parallel to the voltmeter see figure The reading in the voltmeter will be close to 1 12 5 V 3 13 1 V 2 11 9 V 4 24 5 V www 0 6 2 www 10 15 V V

7 A metallic resistor is connected across a battery If the number of collisions of the free electrons with the lattice is somehow decreased in the resistor for example by cooling it then the current will a increase c remain constant b decrease d become zero

conductors made of same material is as shown in th figure Then which of the following is correct 1 Js C 2 Js 2 Js F D A E 3 Js 1 Js B 4 Js

The circuit shown here has two batteries of 8 0 V and 16 0 V and three resistors 30 92 and 992 and a capacitor 5 0 uF How much is the current I in the circuit in steady state 1 1 6 A 2 0 67A 3 2 5 A 4 0 25A 3Q 8 0V 5 F 92 12 9 2 16 0V 2

5 Four cells each of emf E and internal r are connected in series If polarity of one cell is reversed then the terminal voltage across this cell is Er Er Er Er HHWWWWWWWWWWW www 1 E 2 Zero 3 3E 2

0 The figure shows 4n cells connected in series to form a loop r is the internal resistance and E is the emf of each cell If polarity of last 2n cells are reversed then terminal voltage across cell A is 1 Zero 2E 3 3 A 4n cells MMM 2 E 4 E 4 It Aa dis

In the figure the voltages are v t 100 cos wt v t 100 cos wt 18 and v3 t 100 os wt 36 The circuit is in sinusoidal steady state and R WL P P2 and P3 are the average power outputs Which one of the following statements is true R R wwwmmm V t P L mmmmm P tobo V3 t P

wo wires are made of the same material and have the same length but different radii They e joined end to end and a potential difference is maintained across the combination Of the llowing the quantity that is the same for both wires is potential difference current current density electric field conduction electron drift snood

A nichrome wire is 1 m long and 1 x 10 6 m in cross sectional area When connected to a potential difference of 2 V ome is A 10 72 m B 2 x 10 72 m C 4 x 10 72 m D 5 x 10 72 m E 8 x 10 7 m