Current Electricity Questions and Answers

An electric current is passe rough a circuit containing two wires of the same material connected in parallel If the length and radii of the wires are in the ratio of 4 and 2 3 then the ratio of currents passing through the wires will be 1 x then

Q 31 State Kirchhoff s laws On what fact these are based by using these laws find the current flowing through each branch of the given circuit A D 1 5 av Q32 Look at the diagram given below IV 1 B C E

please explain corona discharge and dielectric breakdown of air in short simple words protects a person from lightning strikes if he is in a car v Except for spherical surfaces the charge is not distributed uniformly on the surface of a conductor At the sharp points or edges the surface charge density a is very high and hence the electric field 6 E becomes very strong The air around such sharp points may become ionised producing 0 the corona discharge in which the charge jumps from the conductor to the air because of the dielectric breakdown of the air

density of a piece of a metal of atomic weight 60 are 10 m 1m and 5 x 10 kg m respectively If every atom contributes one free electron and the drift velocity of

The given circuit consists of two ideal batteries two fixed resistances and a variable resistance R Resistance Ris adjusted so that power consumed by it is maximum Choose the correct option s 6 V 12 V R 20 R 30 692 R www wwww 32 Maximum power through R 12 5 W 7 Current through 3 Q resistor is 3 A

In a potentiometer of 10 wires the balance point for measuring the emf of a cell is obtained on 6th wire To shift the balance point on 8th wire we should Decrease resistance in series with the cell whose emf is to be measured Increase resistance in series with the cell whose emf is to be measured Decrease resistance in main circuit in series with potentiometer battery Increase resistance in main circuit in series with potentiometer battery

Two identical bulbs and a heater are connected across a source of constant voltage If one of the bulbs fuses then Heater www OPTIONS MARK FOR REVIEW CLEAR SELECTION A Potential drop across heater increases B Power output of heater will increase c Current through heater increases

For the circuit shown in figure potential difference of 12 Vi applied across AB A 192 www C wwwwww 252 E 2925 2525 32 D 202 F 12 12 V 302 Current drawn through cell is Vo Vol v B A

accelerated we by an electric ted as sOOWD in fig The two stops at the left ensure that the electron beam has a uniform cross I A The speed of the electron is more at B than at A B The electric current is from left to right C The magnitude of the current is larger at B than at A

In a discharge tube the number of proton drifting across any cross section is 1 0x 10 18 per second while the number of electrons drifting in the opposite direction is 1 0 x 10 1 per second If the voltage across the tube is 240V the effective resistance of the tube is x x 10 22 find x values

7 A wire of resistance 402 is bent into a square a resistance between opposite corners is 20 b resistance between adjucent corners is 7 50 c resistance between mid points of opposite sides is 102 d resistance between mid points of adjacent sides is 150 1 a and d are correct2 b and d are correct

A resistor R dissipates the power P when connected to a certain generator If a resistor R is put in series with R the power dissipated by R A decrease C remains the same B increases D any of the above depending upon the relative values of R and R

Three resistances are connected to form the sides of triangle ABC The resistance of the side AB is 40 ohm of the side BC is 60 ohm and its side CA is 100 ohm The effective resistance between points A and B is 80 3 3 3202 1 2 2 2022 4 162

1 When a current of 0 5A is passed through two resistors in series the pd between the ends of the series arrangement is 12 5V On connecting them in parallel and passing a current of 1 5A the pd across them is 6V The two resistances in ohms are 1 5 20 2 5 15 3 5 10 4 15 20

AB BC and CA are three wires of same cross section and are joined to form a triangle Resistance of the three sides are a b and c respectively Another wire of resistance d is taken from A and can be connected at any point on BC Prove that maximum resistance of the network is a b c d a b c 4d O E B i A i i 1 12 13 13 C

Four conductors of same resistance connected to form a square If the resistance between diagonally opposite corners is 8 ohm the resistance between any two adjacent corners is 1 32 ohm 2 8 ohm 4 6 ohm 3 1 6 ohm

5 The resultant resistance of two resistors when connected in series is 9 ohm When they are connected in parallel the resistance is 2 ohm The resistances of these resistors are 1 72 22 2 62 32

16 When a resistance of 2 ohm is placed across a battery the current is 1A and when the resistance across the terminals is 17 ohm the current is 0 25A the emf of the battery is 1 4 5 V 2 5 V 3 3 V 4 6 V

2 In a potentiometer experiment a cell produces balance in the wire at 240 cm Balancing length change to 120 cm when a resistance 202 is connected parallel to the cell Find out the interval resistance of the cell 20

A 4 Q2 resistor in series with 8Q resistance and they are connected to 12V supply if another resistor of 82 is connected across the 82 resistor the current drawn from source would increase or decrease 1 Increases by 25 2 Decreases by 5 3 Increases by 50 4 Decreasesby 50

The value of each resistance of the combinations shown in a Fig 2 72 and b Fig 2 73 is r Determine the equiv alent resistance between the points A and B A www wwwww www Fig 2 72 wwwww B wwww LA B wwwww Fig 2 73 a r b r

9 Six resistors each of value 40 are joined together in a cir cuit as shown in Fig 2 74 Calculate equivalent resistance across the points A and B If the cell of emf 2 V is con nected across AB compute the current through the circuit and the arm DF of the circuit 40 F C A 40 D wwww 42 40 40 wwwE ria 27 Bior CBSE 03 20 1 A 0

With a uniform potentiometer wire AB of resistance 100 an electric cell of emf 2 V and of negligible inter nal resistance is connected A voltmeter of resistance 360 is connected in between the point A and a point C on the wire If the reading in the voltmeter be 0 72 V then in what ratio does the point C divide the wire AB 2 3

A coil of resistance R is connected between the terminals for a battery The quantity of heat produced in 5 minutes is H Now that coil is cut into two equal parts and are connected between the same terminals in parallel This time heat produced in 5 minutes is H Then the ratio of H H is A 1 4 B 4 1

3 In a metre bridge circuit null point is produced at a dis tance 40 cm from A If a resistance 12 is connected in parallel with S null point shifts to 50 cm Determine the value of R and S A R G Fig 77 12 Q Fwww S K B 4 0 6 0

Question No 3 For the circuit shown in figure potential difference of 12 V is applied across www 202 152 C 202 E 352 www 203 0 wwwwwwwwww 32 D 202 F 19 12 V B Current drawn through cell is A

If two bulbs of wattage 25 and 100 respectively each rated at 220 volt are connected in series with the supply of 440 volt which bulb will fuse A 100W bulb C none of them B 25W bulb D both of them

7 The length of the potentiometer wire AB is 100 cm and its resistance is 10 2 Fig 2 68 When AC 40 cm then the null condition of the galvanometer is observed Determine the resistance R A 0 02 V ww 2 V C R wwww B

According to Joule s law if potential difference across a conductor having a material of specific resistance P remains constant then heat produced in the conductor is directly proportional to A p B p C 1 p D 1 p

E I A B S C Three identical that is same resistance lamps A B C are connected to a battery as shown The resistance of the switch S is negligible With the switch S initially op the brightness of that is the power delivered to bulb A is 27 29 W Watts After S is closed this means that the potential difference across the switch vanishes the brightness of the bulb A in W is

equal resistances each of resistance R are connected as shown in figure below A battery of V volt is connected between A and B The current flowing in FC will be D R wwwww R www R OFWwW A R Fig 2 53 R B E

0 In a potentiometer experiment the balancing length with a cell in the secondary circuit is found to be 480 cm When a resistor of 8 ohm is connected in parallel to the cell the balancing length is found to be 420cm The internal resistance of the cell is 1 1 1422 3 4 12 Q 2 252 4 56 Q

3 In a potentiometer experiment a particular cell produces balance in the wire at 560 cm If a 10 2 resistance is con nected with the cell in parallel then this balanced length change to 412 cm Find out the internal resistance of the cell EAMCET 03 3 60 approx

a 4 In a potentiometer the balance length with standard cadmium cell is 509 cm The emf of cell which when connected in the place the standard cell gave a balance length of 750 cm is emf of standard cell is 1 018V 1 1 5V 2 0 5V 3 1 08V 4 1 2V

20 Resistors are connected in the two gaps of meter bridge The balance point is 20 cm from the zero end When a 15 22 resistor is connecte in series with the smaller resistance then the nu point shifts to 40 cm The smaller resistance i 1 802 2 922 3 10 4 12

17 When two unknown resistances are placed in the gaps of meterbridge the null point is found to be 40cm from one end of the bridge wire When one of the resistances is shunted with a 10 ohm coil the null point is 25 cm from the same end The value of each of the unknown resistances is 1 1522 1022 2 102 152 3 20 30 4 30 20

129 The potential gradient along the length of a uniform wire is 10 volt m B and C are two points at 30 cm and 60 cm in a scale fitted along the wire The pd between B and C is 1 3V 2 0 4V 3 7V 4 4V

127 A 10m long wire of resistance 15 ohm is connected in series with a battery of emf 2V no internal resistance and a resistance of 5 ohm The potential gradient along the wire is 1 0 15 Vm 3 15 Vml 2 0 45V m V Val

22 A cell of emf 2 V and negligible resistance is connected in series with a resistance of 5 ohm and a potentiometer wire of resistance 10 ohm What is the potential drop per em if the length of the potentiometer wire is 10 m The emf a cell which is balanced by 750 cm long wire is 1 3 1 P 1500 cm IV 1250 cm 0 5V 0 6V 2 4 750 cm IV 1 V 1V 250 cm

13 In a potentiometer using two cells in series gave a balance length 600cm When the same cells are connected opposing each other then balance length is 100cm The ratio of emfs of the cells is 1 7 5 2 5 7 3 6 1 4 1 6

25 A potentiometer having a wire of 4m longth is connected to the terminals of a battery with a steady voltage A leclanche cell has a null point at 1m If the length of the potentiometer wire is increased by 1m The position of the null point is 1 1 5m 2 1 25m 3 10 05m 4 1 31m

121 1 ohm and 2 ohm are connected in series across the left gap of a metre bridge The balancing length is 60 cm If the resistors were connected in parallel instead of in series the balancing length would be in cm 1 25 2 20 3 40 4 75

In the circuit shown in figure the switch Sis initially open and both the capacitors are initially uncharged Switch Sis closed at t 0 then S R I i at t 0 is C at t 0 is 3R R 4R Diatt is V 4R 6R Electrostatic potential energy stored in the capacitor at steady state is 27 CV

In the figure shown balance point is at 40 cm from A when switch S is open and 60 cm from A when switch S is closed If AB 100 cm the R ww www 10 92 A H 20 V R 12 50 OR 12 50 OR 50 Q 1092 wwww wwwww R B

99 Twenty four cells each of emf 1 5V and internal resistance 0 5 ohms are to be connected to a 3 ohm resistance For maximum current through this resistance what will be the number of rows and number of columns that you connect these cells 1 12 cells in series 2 rows in parallel 2 8 cells in series 3 rows in parallel 3 4 cells in series 6 rows in parallel 4 6 cells in series 4 rows in parallel

102 In a balanced Wheatstone bridge a cell of emf 2 volt is connected between the ends of the diagonal AC What will be the potential difference between the ends of the diagonal B and D 1 Zero 2 2V 3 1V 4 4V

00 A B C and D are four coils of wires of 2 2 2 and 3 ohm resistances respectively and are arranged to form a Wheatstone bridge The resistance which the coil D must be shunted in order that the bridge may be balanced is 1 422 2 6 3 32 4 8

97 When a resistor of 2 is connected across the terminals of a battery a current of 2A is found to flow When a second resistor of 8 is connected in series with the first the current is reduced to 1A The emf and internal resistance of the battery 1 12V 452 2 10V 2Q

0 4 mm diameter copper wire is connected with 2 mm diameter iron wire and 4 mA current is passed through copper wire then current density in iron wire will be A 1 27 x 10 Am B 2x10 Am C 1 5 10 Am Ans 6 A 7 C 8 A 9 B 10 C 11 D 12 B 13 C 14 A 15 B 16 A 16 D 3x10 Am

12 Four resistance P Q R X formed a Wheatstone bridge The bridge is balanced when R 1002 If P and Q are interchanged the bridge balances for R 1212 The value of X is 1 100 S 2 200 S 3 300 S 4 110 S2