Current Electricity Questions and Answers

In the circuit shown in figure A is a sliding contact which can move over a smooth rod PQ Resistance per unit length of the rod PQ is 1 ohm m Initially slider is just left to the point P and circuit is in the steady state At t 0 slider starts moving with constant velocity v 5 m s towards right Current in the circuit at t 2 sec is L 2H R 2092 mooooo A V

D Net magnetic field at point O is zero 25 In the given circuit the point A is 9 V higher than point B Which of the following statements is are CORRECT 26 A A R 10 C B is 3 V lower than D In the circuit shown the current 6 V 10 B 12 V 20 C ALCE 12 V 10 D B R 292 DB is 6 V lower than C a

In the circuit shown in figure Current through R is zero if R 202 and R 42 In this case DIG A Current through R 2 5A C Both a and b are correct P Y 10V R www www 15V R www SV HH www R X B Current through R 3A D Both a and b are wrong

The intrinsic carrier density of a rectangular specimen of Ge is 2 5 10 m The length width and height of the specimen are 20 mm 3 mm and I mm respectively Determine the total current and intrinsic conductivity if a potential difference of 8 V is applied across the length of the specimen Given electron and hole mobility as 0 39 m V s and 0 19 m V s respectively a 2 78 mA 2 32 si m b 2 18 mA 2 02 si m c 2 78 mA 1 32 si m d 1 78 mA 1 32 si m

5 Four cells each of emf 1 9 V and internal resis tance 1 are connected to an external resistance of 18 as shown in the figure Find the terminal potential difference of this combination E E 3 1892 E2 E4

The figure shows a meter bridge wire AC having uniform are of cross section X is a standard resistance of 40 and Yis a resistance coil When Yis immersed in melting ice the null point is at 40 cm from point A When the coil Yis heated to 100 C a resistance of 100 Q has to be connected in parallel with Y in order to keep the bridge balanced at the same point The temperature coefficient of resistance of coil is X 40 Y A 5 x 10 C 2 3 10 4 C 6 3 10 4 C 3 x 10 4 C B D G C

A cell of EMF E and internal resistance r drives a current through an external resistance R Select the incorrect option The cell supplies a power El The heat is produced in Rat the rate El The heat is produced in Rat the rate El R R r The heat is produced in cell at the rate El R r

A certain elastic balloon will support an internal pressure equal to P 100 kPa until the balloon becomes spherical at a diameter of D 1m beyond which P P C x x x D D because of the offsetting effects of balloon curvature and elasticity This balloon contains helium gas at 250 K 100 kPa with a 0 4m volume The balloon is heated until the volume reaches 2 m During the process the maximum pressure inside the balloon is 200 kPa a What is the temperature inside the balloon when pressure is maximum b What are the final pressure and temperature inside the balloon c Determine the work and heat transfer for the overall process R 2 0770kJ kgk c 3 1156kJ kgk 173125K 196 15kPa 2452K 289 77kJ 818kJ

In the circant shown in figure find a www brothersacademy co in a b b ww 1 00 1 12 0V 5 00 www d Brother s Academy LALPUR Campus Circular Road Lalpur Ranchi 834001 Ph 7488408051 8235071441 Brother s Academy DORANDA Campus Opp Eylex Cinemas Hinoo Ranchi 834002 Ph 6201469038 8092071442 0 42 Physics Current Electricity The rate of conversion of internal chemical energy to electrical energy within the battery The rate of dissipation of electrical energy in the battery

tery and the net power and supplied by the battery for external circuit 3 In the circuit shown in figure E 7V E 1V R 202 and R 302 respectively Find the power supplied by the two batteries E R www www R www R3 E

A resistance of RQ draws current from a potentiometer Potentiometer has a total resistance Roas shown in figure 1 A 3 2V R Ro 4R R A voltage V is supplied to the potentiometer Derive an expression for the voltage across R when the sliding contact is in the middle of the potentiometer 4V R Ro 2R R B 2 4 2V R Ro C 2V Ro Ro 4R

The plot represents the flow of current through a wire at three different time intervals 0 2 3 5 6 8 The ratio of charges flowing through the wire at different time intervals is 2 i A 2 X2 1 2 1 1 1 1 3 3 2 2 3 3 4 5 6 8 t s

At t 0 switch S is closed Current through switch as a function of time t is wwwwwww 222 4922 302 wwwwwww C 7F S HH 2 2 222 wwwwww 192 20 V 1 i t 5e 0 125 t A 2 i t 4e 0 125 t A 3 i t 2e 0 75 t A 4 i t 4e 0 75 t A

The reading of voltmeter in the circuit shown is 6 V 40 2 www 60 9 www V 40 9

In the circuit shown the cell has an emf of 10 V and internal resistance of 1 ohm the other resistance are shown in the figure The potential difference is 6 V 4 V 2 V E 10V r 12 40 wwwww 22 A B H 20 www 40 www 19

44 Time required for making a print at a distance of 40 cm from a 60 watt lamp is 12 8 second If the distance is decreased to 25 cm then time required in making the similar print will be a 15 sec c 5 sec b 10 sec d Remains some

5 a Find the Thevenin equivalent circuit of the circuit shown in Fig to the left of the terminals Then find the current through RL 6 16 and 3692 492 192 a 32 V 1292 12 V www Or b Using Thevenin s theorem find I 69 www 69Q www 2 A www 2 A 492 b b 19 RL

A 200 MVA synchronous generator having inertia constant 5MJ MVA is connected in parallel with a 150 MVA generators having inertia constant of 4 MJ MVA both the generator are swinging coherently the equivalent inertia constant of the machine on a base of 100 MVA is in MJ MVA

3 5 In the circuit shown in figure 3 376 E 5V r 19 R 40 R3302 and C 3uF Find the charge on the plates of capaictor A F ib HH C C R www R www R3 www Figure 376 HH C C

Assertion A Earthing provides a safety measure for electrical circuits and appliances Reason R When we bring a charged body in contact with the earth all the excess charge on the body disappears by causing a momentary current to pass to the ground through the connecting conductor A A

A cylindrical rod is reformed to half of its original length keeping volume constant If its resistance before this change were R then the resistance after reformation of rod will be R b R 4 RIA c 3R 4 d R 2

An certain resistor dissipates 0 5 W when connected to a 3 V potential difference When con nected to a 1 V potential difference this resistor will dissipate A 0 5 W B 0 167 W C 1 5 W D 0 056 W E none of these Test

To get maximum current through a resistance of 2 5 Q one can use m rows of cells each row having n cells The internal resistance of each cell is 0 5 Q What are the values of n m if the total number of cells is 45 3 15 5 9 X 9 5

10 kJ s of heat is produced when a DC flows through a 100 Q resistor Which of the following ac produces nearly same heat per sec through the same resistor 1 15 sin ot 3 30sin ot 2 45 sin wty 4 10 sin ot

kii 12 wires each of resistance r are connected in the form of 12 sides of a cube Effective resistance across a Diagonally opposite corners 5r 6 b Face diagonal 3r 4 c two adjacent corners 7r 12

A capacitor of capacity C is charged to a potential difference V and another capacitor of capacity 2 C is charged to a potential difference 2 V The charging batteries are disconnected and the two capacitors are connected to each other in parallel with reverse polarity The energy lost in this process will be 1 CV 2 3 C 2 2 CV

You buy a 75 W light bulb The label means that A no matter how you us B the bulb was filled with 75 W at the factory C the actual power dissipated will be much higher than 75 W since most of the power appe as heat D the bulb is expected to burn out after you use up its 75 W E none of the above

The cylinder is changed to one with the same mass and radius but a different moment of inertia Starting from rest the mass now moves a distance of 0 492 m in a time of 0 510 s Find Icm of the new cylinder

A point light source is located at a distance L from a screen A thir converging lens of focal length f L 4 and aperture radius R hel parallel to the screen makes a circular spot of light on the screen If len is moved from the source towards the screen size of the spot varies Fin the radius of the smallest light spot which can be obtained in this wa on the screen R FL 2VFL 2

10 In the Bohr model of hydrogen atom the electron rotates in a circle of radius 0 53 about the nucleus Calculate the energy in eV needed to tear the electron loose from the nucleus of the atom Ans 13 6 eV

If the current sensitivity of a moving coil galvanometer is increased by 20 its resistance also increases and becomes 1 5 times then the voltage sensitivity of galvanometer will Increase by 20 Increase by 50 Decrease by 25 Decrease by 20

Coefficient of linear expansion of material of resistor is a Its temperature coefficient of resistivity and resistance area and a respectively then correct relation is 1 R aR a dp 2 R p 3 OR p 3

D Two converging lenses of focal lengths f 20 cm and f2 10 cm are placed with their optical axes coinciding A rectangle of sides a 1 mm and b 2 mm is placed in front of the first lens with its side a on the common optical axis of the lenses If the image formed by this system of lenses is real and also a rectangle find distance between the lenses and sides a2 and be of the image d fit 30cm 15mm az a 12 fill

Q 60 AB and CD are two resistance wires cut from a uniform long wire Lengths of AB and CD are L and 2L respectively and resistance of AB is R The two resistances are connected in parallel to a supply P and Q are two points on the resistance AB such that AP QB Two conductors PS and QT are connected between two resistors such that no current flows through both the conductors A resistance R is connected between points M and N as shown Neglect resistance of PS and QT a Find the equivalent resistance of the circuit between X and Y b Will there be any current in resistance connected across MN X A P M www QB N D Y

6 A common emitter amplifier has a voltage gain of 50 an input impedance of 10002 and an output impedance of 2002 The power gain of the amplifier is a 1000 2007 c 100 b 1250 d 500 tructure which one of the

1 Consider a resistor with length L uniform cross sectional area A and uniform resistivity p that is carrying a current with uniform current density J Find the electric power dissipated per unit volume p Express your result in terms of i E and J ii J and p

The resistance of each arm of a Wheat stone bridge is 100 A resistance of 10 2 is connected in series with the galvanometer then the equivalent resistance across the battery will be 1 10 22 3 20 2 15 4 40

48 The equivalent resistance of series combination of four equal resistors is S If they are joined in parallel the total resistance is P The relation between Sand P is given by S nP Then the minimum possible value of n is a 12 d 10 b 14 c 16

5 In a typical Wheatstone bridge the resistance in cyclic order are A 10 Q2 B 522 C 40 and D 42 For the bridge to be balanced A 10 0 www wwww D 40 www B 5 Q C 402 www a 10 2 should be connected in parallel with A b 10 2 should be connected in series with A c 5 2 should be connected in series with B d 5 2 should be connected in parallel with B 1 a b 2 b c 3 a c 4 all CE006

Four identical electrical lamps are labelled 1 5V 0 5A which describes the condition necessary for them to operate at normal brightness A 12V battery of negligible internal resistance is connected to lamps as shown then 10 e R The value of R for normal brightness of each lamp is 3 4 W The value of R for normal brightness of each lamp is 21 4 w Total power dissipated in circuit when all lamps are normally bright is 24W Power dissipated in R is 21W when all lamps are normally bright

12 A 5 80 m length of 2 0 mm diameter wire carries a 750 mA current when 22 0 mV is applied to its ends the drift speed is 1 7 x 10 m s determine T2 500 C a The resistance R of the wire b The resistivity p and c The number n of free electrons per unit volume 3 At a point high in the Earth s atmosphere He ions in a concentration of 2 8 x 1012 m are moving due north at a speed of 2 0 x 106 m s Also a 7 0 x 1011 m concentration of O ions is moving due south at a speed of 7 2 x 106 m s Determine the magnitude and direction of the net current passing through unit area A m

Each potassium atom contributes one electron to the electron gas Calculate a the Fermi energy b the Fermi momentum c the Fermi temperature and d the contribution of free electrons to the specific heat capacity at 100 K Given N V 1 33 x 10 m

Silver and copper voltameter are connected in parallel with a battery of e m f 12 V In 30 minutes 1 gm of silver and 1 8 gm of copper are liberated The power supplied by the battery is ZCu 6 6x10 4gm C and ZAg 11 2x10 4gm C A B C 24 13 J sec 2 413 J sec 0 2413 J sec 2013 oc

The system shown is in vertical plane Mass of L shaped rod is 2m and coefficient of friction between 2m and rod is 0 5 Then take ideal pulleys and ideal threads m A Acceleration of mass is zero 2 5mg B Tension T in the thread marked in diagram is 4 mg C Friction force between 2m and rod is 2 D Acceleration of L shaped rod is 8 T M O 2m N 3

134 The potential differences across the resistances are given in the following circuit as shown If point Q is grounded the potential at point S will be P Q R S a 20 V c 50 V www 25 V ww 20 V 100 V 30 V b d ww 25 V 20 V 50 V T

switch S is shown in figure The switch S is in position 1 Find the potential difference V VB If now the switch S is put in position 2 at t 0 Find steady current in R4 2 R 20 R 202 A E 11V 3V L R ww 202 C 2 F 34 In R B 30 R

fastened to a weight of 5 gram by threads float in equilibrium as shown in Fig 1 a 27 Calculate FIGURE 1 a 27 A 0 6m OB e 0101 1m 1m O fom 00 1 the charge on each balloon assuming that they

A conductor with rectangular cross section ha dimension ax 2a x 4a as shown in figure Resistance across AB is x across CD is y and acros EF is z then ratio of x y z is A E 1 16 4 1 C 4a D F 2a a B 2 16 1 4

Consider the two circuits below in which the left resistor is 100 and the right one is 30 2 Use your understanding of voltage resistance and current to answer these questions A What do you think will happen when the switches are closed B How will the brightness of the left light compare to the brightness of the right light

WB JEE 1 The effective resistance between A and B in the figure 7 is if each side of the cube has 12 resistance 12 The effective resistance between the same two points when the link AB is removed is B a b c 7 12 5 2 C 5 QA 12 d 2 7 AND