Current Electricity Questions and Answers

B In India electricity is supplied for domestic use at 220 V It is supplied at 110 V in USA If the resistance of a 60 W bulb for use in India is R the resistance of a 60 W bulb for use in USA will be 1 R 2 2R R 3 R 4

the value of the five band Resister using color code table The nominal value is The tolerance is The Max value is The Min value is Yellow brey Black Black Color Digit Multiplier Tolerance 9 Black Brown Red 1 2 Orange Yellow Green Blue 3 4 5 6 10 1 10 10 10 10 10 10 1 2 10 5 0 25

10 Refer to the figure given below use it to find the equivalent resistance across the points a b If a potential difference of 12 V is applied across the points a b calculate the total current flowing in the circuit 592 ww a 10 2 m 25 92 www 592 20 Q w m 592 b

The value of the resistance R in figure is adjusted such that power dissipated in the 2 2 resistor is maximum Then the power dissipated in the 2 will be 12 V 8Q www R 202

8 In the circuit shown there are n repetitions of the same loop What resistance Ro should be connected across the end points so that the equivalent resistance between a and b may be independent of n What is this equal to a www www www www www ww www R

6 A potentiometer wire has length 4 m and resistance 8 22 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 2015 a 40 b 44 S c 48 d 32 S

In a RLC series circuit shown the readings of voltmeters V and V are 100 V and 120 V respectively If source voltage is 130 V a Voltage across resistor is 50 V b Voltage across inductor is 86 6 V c Voltage across capacitor is 206 6 V d all of these R www V 0000 V

A balanced star connected load has an impedance of 6 3j per phase The line voltage is Vab 11020 Find a The phase voltages b The phase currents C The line currents d Power factor e Average power f Reactive power

a V depends on I non linearly b the relation between Vand I depends on the sign of V for the same v absolute value of V c The relation between V and I is non unique An example of a is when p increases with I even if temperature is kept fixed A rectifier combines features a and b GaAs shows the feature e When a source of emf is connected to an external resistance R the voltage Vacross R is given by E R r IR I DUAL CAMER hot by Sout R

A source of voltage V is connected to a resistance R and two ideal inductors L1 and L2 through a switch S as shown There is no mutual inductance b w the two inductors The switch S is initially open At t 0 the switch is closed and current begins to flow Find current through L1 and L2 at any time S www R

An electrical dipole of moment p is placed in an electric field of intensity E The dipole acquires a position such that the axis of the dipole makes an angle 0 with the direction of the field Assuming that the potential energy of the dipole is zero when 0 90 the torque and the potential energy of the dipole will be respectively 1 p E sine 2p E cose 2 p E cose p E sine 3 p E sin0 p E cose 4 p E sine 2p E cose

14 Two resistances are connected in two gaps of metre bridge The balance point is 20 cm from the zero end A resistance of 15 22 is connected in series with the smaller of the two The null point shifts to 40 cm The value of the smaller resistance in ohm is c 9 d 12 a 3 b 6

The figure shows the network of resistances connected across the cell of unknown emf E Mark the correct statement s gut each of I g qua Mfg 692 502 A B C D fa A uz 292 6A Www 302 www 392 wwww R 492 10 A Correct Answer 492 6 V The value of unknown resistance R 90 R 90 mm 452 www 1 5 A 13 0 4 0 2 A 3 10 A 4 10 A The emf of the source is 117 V 117 V Correct Answer

The value of time constant for the electric circuit shown in the figure is r is the internal resistance of the cell of emf E E 2V A B www C Select an answer r 122 ww R 92 15 s 1 5 s L 100 mH 0 15 s R 2002

The potential at the terminals of the battery falls from 9V on open circuit to 6 volts when a resistor of 100 is connected across its terminals What is the internal resistance of the battery The equivalent resistance of 3 resistors A B C connected in parallel is 1 7140 If A is twice of B and C is half as much as B find the equivalent resistance when the three of them are connected in series

The electromotive force of a standard cell is measured with a potentiometer that gives reading of 1 3562 V When a 1 MQ resistor is connected across the standard cell terminals the potentiometer reading drops to 1 3560 V What is the internal resistance of the standard cell A 120 V DC motor draws a current of 100 A and is located 1000 ft from the supply source If the diameter of the copper transmission line is 0 45 inch what must be the voltage of the supply

TU The current in an AC circuit is given by sin 50m t where t is in second The time interva in which it will reach from zero to its peak value NCERT Pg 234 1 10 ms 2 5 ms 3 20 ms

In the circuit shown in figure capacitor was initially uncharged switch is closed at t 0 Select correct alternatives 1 2 MS 48V 600 k Correct wwww The initial battery current immediately after switch Sis closed is 40 A 2 5 F The time after which current the Prev 17 a Next The battery current long time after switch S is closed is S A Correct The current through the 600k as a function of time is

Find the voltage cross and current through R1 in the circuit shown below using Superposition Theorem V1 XC1 j40 HE C1 16Vrms 200Hz 0 3 0 R1 XC2 j40 C2 V2 8Vrms 200Hz 0

14 At time t 0 a battery of 10 V is connected across points A and B shown in figure If the capacitors have no change initially at what time does the voltage across becomes 4V 2 MQ a 2s C 4s A 2 MQ 2 F HH 2 F b 3s d 5s B

The values of two resistors are R 6 0 3 k and R 10 0 2 k The percentage error in the equivalent resistance when they are connected in parallel is 1 5 125 3 3 875 2 2 4 7

D For different values of resistance R power consumptions in R are given Then which of the following values are not possible a 2 W c 8 W 1 Only c 3 a b c 4 V www 12 ww R b 5 W d 4 W 2 b c 4 All

Q 64 In the circuit shown in figure a the emf of the ideal cell is E 100 V and resistance R is 10 2 The current I Voltage V characteristic of the circuit contained in box A is as shown in figure b Find the potential difference across the box A A www R E a Let current in the circuit be 1 Potential difference across A is V E IR Using 1 Current through the box is 1 A or V 100 10 I Current through R connected in parallel to A is 7 Plot the equation 2 on the given graph 2 0 10 25 V 100 101 R 10 10 b i 1 l i 1 10 1 21 10 V I 10 10 1 2 10 10 10 I 10 5 10 I V Volt 10 5 1 O 10 2 25 50

37 All the bulbs shown in the figure are identical and are rated to fuse if the voltage across the bulb exceeds 200V The bulb s which will fuse in the circuit on closing the switch is 1 B 3 B S B B B3 B 52 52 300 V 2 B 4 no bulb will fuse

7 Write the relation between relative permeability and magnetic susceptibility Section C Each Question carries 2 marks 10 1 A galvanometer of resistance 100 gives a full scale deflection for a current of 2 m How will you use it to measure voltage up to 10 V 2 State Lenz s law and explain how magnet s motion creates a magnetic dipole in the 3 Define magnetic dipole moment for a current roll

Sir please explain why emf decrease with time and why ternal resistance increase with time 21 Assertion EMF of battery decreases with time AIIMS 2016 Reason Internal resistance increases with time 1 A 2 B 3 C 4 D

Four circuits are shown below All the batteries have the same voltage Vand all resistors have the same resistance R In which circuit does the battery delivers the most power 1 R R R R 2 R R R R

6 In a series resonant LCR circuit the voltage across R is 100 V and R 1k2 with C 2uF The resonant frequency w is 200 rad s At resonance the voltage across Lis a 4x10 V C 40 V b 2 5 10 2V d 250V

Two cells each of e m f E and internal resistance r are connected in parallel across a resistor R The power dissipated in the resistor is maximum if 1 R r 2 R 2r 3 R 3r 2 4 R 2

Write a matrix equation that determines the loop currents 1228 29 V 36 V 852 392 4 2 5021 10 V 592 692 13 292 20 V C For each matrix let row 1 correspond to loop 1 row 2 correspond to loop 2 and so on Also enter positive values for positive voltages and negative values for negative voltages 1 12 13 14

Two wires of same material and same length are connected to two gaps of a meter bridge The balancing length measured from left gap is 25 cm The ratio of radius of two wires in left gap to that in the right gap is 03 1 05 1 01 9 03 2

Four wires of the same diameter are connected in turn between two points maintained at a constant potential difference Their resistivities and lengths are respectively p and L wire 1 1 2 p and 1 2 L wire 2 0 9 p and 0 9 L wire 3 and p and 1 5 L wire 4 Rank the wires according to the rates at which energy is dissipated as heat greatest first 1 4 3 1 2 3 1 2 3 4 2 4 2 1 3 4 3 1 2 4

You are provided with 48 cells each of emf 2 volts and internal resistance 4 ohms What maximum current can flow in the circuit having an external resistance of 12 1 1 A 2 1 2 A 3 0 96 A

A resistance coil wired to an external battery is placed inside a thermally insulated cylinder fitted with a frictionless piston and containing an ideal gas A current I 240 mA flows through the coil which has a resistance R 500 22 At what speed v in cm s must the piston of mass m 48 kg move upward in order that the temperature of the gas remains unchanged Assume that the cylinder is placed in vacuum I Gas www R

26 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 E r E rE rE r ww HHWWWWWWW m ww 3 1 E 2 Zero 3E

For the circuit shown in the adjacent figure select the correct statements from the following A B B 20 www www B ww 20 Fund www B a x and y are equipotential points b Effective resistance between A and B is 20 c Effective resistance between A and B is 192 d None of the above

ons on it is Q 25 Using a long extension cord in which each conductor has a resistance 8Q a bulb marked on olas 100 W 200 V is connected to a 220 V dc supply of negligible internal resistance as shown in figure Power delivered to the bulb is W 220V I 892 www 8 2 www 258 S R 48492

A 18 V battery with internal resistance 0 5 is connected across a variable resistance R The value of R for which the power delivered to it is maximum is equal to 1 0 5 2 12 3 1 5 Q 4 20

Two heating coils A and B are used to heat water When coil A is supplied a constant voltage V it heats 1 kg water from 20 C to 60 C in 10 minutes When coil B is supplied a constant voltage V it heats 1 kg water from 20 C to 80 C in 5 minutes Now the coils are connected in series and the combination is supplied a constant voltage V The temperature starting from 20 C to which the coils heat 1 kg of water in 15 minutes is C Assume that water is heated in insulated vessels such that the heat loss to the surroundings is negligible

A nichrome wire of uniform cross sectional area is bent to form a ractangular loop ABCD Another nichrome wire of the same cross sectional is connected to from the diagonal AC If the potential difference across BD is VBD the ratio of is found 1 12 to be n where n is an integer What is the value of n Given AB 4 units and BC 3 units I D H I 2 I

In the given figure point B and C are earthed potential difference between point A and B is 10V 1 4V 3 9V www 192 B C 521092 1532 D 2 5V 4 10V

3 What will be respectively the potential and electric field in the above set up if the consecutive charges have opposite sign 9 1 65 E 2 3 9 62 Es 9 5m o and and and 9 5m E 9 4t E 9 6A E

cells in series but one 4 A person connects four cell has its terminals reversed The external resistance is 192 If each cell has an e m f of 1 5 V the current flowing is A Zero 3 C A 4 B 3 2 4 3 A D A

EXERCISE Find equivalent resistance between A and B R A WW Be KR www KR www k R www k R www Fig 25 58 HINT Let RB x then the resistance of the broken chain will be kx Ans R 2k 1 4k 1 2k

In the given diagram choose correct options The value of I is 4A The current from the cell is 4A Voltage drop across AB is 140 V The current from the cell is 10A 10A 6A 592 1092 B 502 1002 592 1092 200V 592

A part of a larger circuit is shown in the figure Both batteries shown have internal resistance 10 each If the points A and B are equipotential and a current 2 A flows from A towards B then the emf E in Volts is B A www 312 SV www 202 43

2 Two charged balls of the same radius and weight suspended on threads of equal length are immersed into a liquid having density of d and a dielectric constant K The density d of the material of the balls for the angles of divergene of the threads in the air and in the dielectric to be the same is Kd 1 d 2 4 Kd K 1

A group of 12 resistors is arranged along the edges of a cube as shown in the diagram The vertices of the cube are labeled a h The resistance between each pair of vertices is as follows 30 ww 30 30 120 22 ww 80 1202 W 1202 15 802 102 W 10 R R R 3 00 R R R 800 R R R 12 00 R R R 1 00 What is the equivalent resistance between points a and h 19 1 2 3 22 15 02 4 44 7 2 IN HARDLOOPPAPATE

39 A small ball having charge q is suspended from a weightless inextensible string It is placed in a region of uniform electric field E 3 10 N C as shown in figure In equilibrium the string is making an angle of 30 with the vertical If the mass of the ball is 3 3 g the charge on it is g 10ms

The heating coil of an electric heater should be made with material which has A low specific resistance and low melting point B high specific resistance and low melting point C low specific resistance and high melting point D high specific resistance and high melting point